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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>SafePrelude</title><link href="ocean.css" rel="stylesheet" type="text/css" title="Ocean" /><script src="haddock-util.js" type="text/javascript"></script><script src="https://cdn.mathjax.org/mathjax/latest/MathJax.js?config=TeX-AMS-MML_HTMLorMML" type="text/javascript"></script><script type="text/javascript">//<![CDATA[
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window.onload = function () {pageLoad();setSynopsis("mini_SafePrelude.html");};
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//]]>
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</script></head><body><div id="package-header"><ul class="links" id="page-menu"><li><a href="src/SafePrelude.html">Source</a></li><li><a href="index.html">Contents</a></li><li><a href="doc-index.html">Index</a></li></ul><p class="caption">safe-prelude-0.1.0.0: A Haskell prelude optimized for safety</p></div><div id="content"><div id="module-header"><table class="info"><tr><th>Safe Haskell</th><td>None</td></tr><tr><th>Language</th><td>Haskell2010</td></tr></table><p class="caption">SafePrelude</p></div><div id="table-of-contents"><p class="caption">Contents</p><ul><li><a href="#g:1">Types</a><ul><li><a href="#g:2">Numbers</a></li></ul></li><li><a href="#g:3">Type classes</a><ul><li><a href="#g:4">Numeric</a></li></ul></li><li><a href="#g:5">Functions</a><ul><li><a href="#g:6">Numeric</a></li><li><a href="#g:7">Foldable</a></li><li><a href="#g:8">Traversable</a></li><li><a href="#g:9">Functor</a></li><li><a href="#g:10">Applicative</a></li><li><a href="#g:11">Alternative</a></li><li><a href="#g:12">Monad</a></li><li><a href="#g:13">Concurrent</a></li><li><a href="#g:14">Reader</a></li><li><a href="#g:15">Exceptions</a></li><li><a href="#g:16">Arrow</a></li><li><a href="#g:17">Maybe</a></li><li><a href="#g:18">Either</a></li><li><a href="#g:19">Ord</a></li><li><a href="#g:20">Say</a></li><li><a href="#g:21">IORef</a></li><li><a href="#g:22">IO</a></li><li><a href="#g:23">Character encoding</a></li><li><a href="#g:24">deepseq</a></li><li><a href="#g:25">Monoids</a></li><li><a href="#g:26">Read</a></li></ul></li></ul></div><div id="synopsis"><p id="control.syn" class="caption expander" onclick="toggleSection('syn')">Synopsis</p><ul id="section.syn" class="hide" onclick="toggleSection('syn')"><li class="src short"><span class="keyword">data</span> <a href="#t:Maybe">Maybe</a> a :: <a href="../base-4.9.0.0/Data-Kind.html#t:-42-">*</a> -> <a href="../base-4.9.0.0/Data-Kind.html#t:-42-">*</a><ul class="subs"><li>= <a href="#v:Nothing">Nothing</a></li><li>| <a href="#v:Just">Just</a> a</li></ul></li><li class="src short"><span class="keyword">data</span> <a href="#t:Ordering">Ordering</a> :: <a href="../base-4.9.0.0/Data-Kind.html#t:-42-">*</a><ul class="subs"><li>= <a href="#v:LT">LT</a></li><li>| <a href="#v:EQ">EQ</a></li><li>| <a href="#v:GT">GT</a></li></ul></li><li class="src short"><span class="keyword">data</span> <a href="#t:Bool">Bool</a> :: <a href="../base-4.9.0.0/Data-Kind.html#t:-42-">*</a><ul class="subs"><li>= <a href="#v:False">False</a></li><li>| <a href="#v:True">True</a></li></ul></li><li class="src short"><span class="keyword">data</span> <a href="#t:Char">Char</a> :: <a href="../base-4.9.0.0/Data-Kind.html#t:-42-">*</a></li><li class="src short"><span class="keyword">data</span> <a href="#t:IO">IO</a> a :: <a href="../base-4.9.0.0/Data-Kind.html#t:-42-">*</a> -> <a href="../base-4.9.0.0/Data-Kind.html#t:-42-">*</a></li><li class="src short"><span class="keyword">data</span> <a href="#t:Either">Either</a> a b :: <a href="../base-4.9.0.0/Data-Kind.html#t:-42-">*</a> -> <a href="../base-4.9.0.0/Data-Kind.html#t:-42-">*</a> -> <a href="../base-4.9.0.0/Data-Kind.html#t:-42-">*</a><ul class="subs"><li>= <a href="#v:Left">Left</a> a</li><li>| <a href="#v:Right">Right</a> b</li></ul></li><li class="src short"><span class="keyword">data</span> <a href="#t:ByteString">ByteString</a> :: <a href="../base-4.9.0.0/Data-Kind.html#t:-42-">*</a></li><li class="src short"><span class="keyword">data</span> <a href="#t:Text">Text</a> :: <a href="../base-4.9.0.0/Data-Kind.html#t:-42-">*</a></li><li class="src short"><span class="keyword">data</span> <a href="#t:Map">Map</a> k a :: <a href="../base-4.9.0.0/Data-Kind.html#t:-42-">*</a> -> <a href="../base-4.9.0.0/Data-Kind.html#t:-42-">*</a> -> <a href="../base-4.9.0.0/Data-Kind.html#t:-42-">*</a></li><li class="src short"><span class="keyword">data</span> <a href="#t:HashMap">HashMap</a> k v :: <a href="../base-4.9.0.0/Data-Kind.html#t:-42-">*</a> -> <a href="../base-4.9.0.0/Data-Kind.html#t:-42-">*</a> -> <a href="../base-4.9.0.0/Data-Kind.html#t:-42-">*
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<code><code><a href="SafePrelude.html#t:Maybe">Maybe</a></code> a</code> either contains a value of type <code>a</code> (represented as <code><code><a href="SafePrelude.html#v:Just">Just</a></code> a</code>),
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or it is empty (represented as <code><a href="SafePrelude.html#v:Nothing">Nothing</a></code>). Using <code><a href="SafePrelude.html#t:Maybe">Maybe</a></code> is a good way to
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deal with errors or exceptional cases without resorting to drastic
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measures such as <code><a href="../base-4.9.0.0/Prelude.html#v:error">error</a></code>.</p><p>The <code><a href="SafePrelude.html#t:Maybe">Maybe</a></code> type is also a monad. It is a simple kind of error
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monad, where all errors are represented by <code><a href="SafePrelude.html#v:Nothing">Nothing</a></code>. A richer
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error monad can be built using the <code><a href="../base-4.9.0.0/Data-Either.html#v:Either">Either</a></code> type.</p></div><div class="subs constructors"><p class="caption">Constructors</p><table><tr><td class="src"><a id="v:Nothing" class="def">Nothing</a></td><td class="doc empty"> </td></tr><tr><td class="src"><a id="v:Just" class="def">Just</a> a</td><td class="doc empty"> </td></tr></table></div><div class="subs instances"><p id="control.i:Maybe" class="caption collapser" onclick="toggleSection('i:Maybe')">Instances</p><div id="section.i:Maybe" class="show"><table><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:id:Maybe:Monad:1" class="instance expander" onclick="toggleSection('i:id:Maybe:Monad:1')"></span> <a href="SafePrelude.html#t:Monad">Monad</a> <a href="SafePrelude.html#t:Maybe">Maybe</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:id:Maybe:Monad:1" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:-62--62--61-">(>>=)</a> :: <a href="SafePrelude.html#t:Maybe">Maybe</a> a -> (a -> <a href="SafePrelude.html#t:Maybe">Maybe</a> b) -> <a href="SafePrelude.html#t:Maybe">Maybe</a> b <a href="#v:-62--62--61-" class="selflink">#</a></p><p class="src"><a href="#v:-62--62-">(>>)</a> :: <a href="SafePrelude.html#t:Maybe">Maybe</a> a -> <a href="SafePrelude.html#t:Maybe">Maybe</a> b -> <a href="SafePrelude.html#t:Maybe">Maybe</a> b <a href="#v:-62--62-" class="selflink">#</a></p><p class="src"><a href="#v:return">return</a> :: a -> <a href="SafePrelude.html#t:Maybe">Maybe</a> a <a href="#v:return" class="selflink">#</a></p><p class="src"><a href="#v:fail">fail</a> :: <a href="SafePrelude.html#t:String">String</a> -> <a href="SafePrelude.html#t:Maybe">Maybe</a> a <a href="#v:fail" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:id:Maybe:Functor:2" class="instance expander" onclick="toggleSection('i:id:Maybe:Functor:2')"></span> <a href="SafePrelude.html#t:Functor">Functor</a> <a href="SafePrelude.html#t:Maybe">Maybe</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:id:Maybe:Functor:2" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:fmap">fmap</a> :: (a -> b) -> <a href="SafePrelude.html#t:Maybe">Maybe</a> a -> <a href="SafePrelude.html#t:Maybe">Maybe</a> b <a href="#v:fmap" class="selflink">#</a></p><p class="src"><a href="#v:-60--36-">(<$)</a> :: a -> <a href="SafePrelude.html#t:Maybe">Maybe</a> b -> <a href="SafePrelude.html#t:Maybe">Maybe</a> a <a href="#v:-60--36-" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:id:Maybe:Applicative:3" class="instance expander" onclick="toggleSection('i:id:Maybe:Applicative:3')"></span> <a href="SafePrelude.html#t:Applicative">Applicative</a> <a href="SafePrelude.html#t:Maybe">Maybe</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:id:Maybe:Applicative:3" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:pure">pure</a> :: a -> <a href="SafePrelude.html#t:Maybe">Maybe</a> a <a href="#v:pure" class="selflink">#</a></p><p class="src"><a href="#v:-60--42--62-">(<*>)</a> :: <a href="SafePrelude.html#t:Maybe">Maybe</a> (a -> b) -> <a href="SafePrelude.html#t:Maybe">Maybe</a> a -> <a href="SafePrelude.html#t:Maybe">Maybe</a> b <a href="#v:-60--42--62-" class="selflink">#</a></p><p class="src"><a href="#v:-42--62-">(*>)</a> :: <a href="SafePrelude.html#t:Maybe">Maybe</a> a -> <a href="SafePrelude.html#t:Maybe">Maybe</a> b -> <a href="SafePrelude.html#t:Maybe">Maybe</a> b <a href="#v:-42--62-" class="selflink">#</a></p><p class="src"><a href="#v:-60--42-">(<*)</a> :: <a href="SafePrelude.html#t:Maybe">Maybe</a> a -> <a href="Saf
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<a href="http://en.wikipedia.org/wiki/Monoid">http://en.wikipedia.org/wiki/Monoid</a>: "Any semigroup <code>S</code> may be
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turned into a monoid simply by adjoining an element <code>e</code> not in <code>S</code>
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and defining <code>e*e = e</code> and <code>e*s = s = s*e</code> for all <code>s ∈ S</code>." Since
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there is no "Semigroup" typeclass providing just <code><a href="SafePrelude.html#v:mappend">mappend</a></code>, we
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use <code><a href="SafePrelude.html#t:Monoid">Monoid</a></code> instead.</p></td></tr><tr><td colspan="2"><div id="section.i:id:Maybe:Monoid:16" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:mempty">mempty</a> :: <a href="SafePrelude.html#t:Maybe">Maybe</a> a <a href="#v:mempty" class="selflink">#</a></p><p class="src"><a href="#v:mappend">mappend</a> :: <a href="SafePrelude.html#t:Maybe">Maybe</a> a -> <a href="SafePrelude.html#t:Maybe">Maybe</a> a -> <a href="SafePrelude.html#t:Maybe">Maybe</a> a <a href="#v:mappend" class="selflink">#</a></p><p class="src"><a href="#v:mconcat">mconcat</a> :: [<a href="SafePrelude.html#t:Maybe">Maybe</a> a] -> <a href="SafePrelude.html#t:Maybe">Maybe</a> a <a href="#v:mconcat" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:id:Maybe:Lift:17" class="instance expander" onclick="toggleSection('i:id:Maybe:Lift:17')"></span> <a href="../template-haskell-2.11.0.0/Language-Haskell-TH-Syntax.html#t:Lift">Lift</a> a => <a href="../template-haskell-2.11.0.0/Language-Haskell-TH-Syntax.html#t:Lift">Lift</a> (<a href="SafePrelude.html#t:Maybe">Maybe</a> a)</span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:id:Maybe:Lift:17" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:lift">lift</a> :: <a href="SafePrelude.html#t:Maybe">Maybe</a> a -> <a href="../template-haskell-2.11.0.0/Language-Haskell-TH-Syntax.html#t:Q">Q</a> <a href="../template-haskell-2.11.0.0/Language-Haskell-TH-Syntax.html#t:Exp">Exp</a> <a href="#v:lift" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:id:Maybe:NFData:18" class="instance expander" onclick="toggleSection('i:id:Maybe:NFData:18')"></span> <a href="SafePrelude.html#t:NFData">NFData</a> a => <a href="SafePrelude.html#t:NFData">NFData</a> (<a href="SafePrelude.html#t:Maybe">Maybe</a> a)</span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:id:Maybe:NFData:18" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:rnf">rnf</a> :: <a href="SafePrelude.html#t:Maybe">Maybe</a> a -> () <a href="#v:rnf" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:id:Maybe:Hashable:19" class="instance expander" onclick="toggleSection('i:id:Maybe:Hashable:19')"></span> <a href="SafePrelude.html#t:Hashable">Hashable</a> a => <a href="SafePrelude.html#t:Hashable">Hashable</a> (<a href="SafePrelude.html#t:Maybe">Maybe</a> a)</span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:id:Maybe:Hashable:19" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:hashWithSalt">hashWithSalt</a> :: <a href="SafePrelude.html#t:Int">Int</a> -> <a href="SafePrelude.html#t:Maybe">Maybe</a> a -> <a href="SafePrelude.html#t:Int">Int</a> <a href="#v:hashWithSalt" class="selflink">#</a></p><p class="src"><a href="#v:hash">hash</a> :: <a href="SafePrelude.html#t:Maybe">Maybe</a> a -> <a href="SafePrelude.html#t:Int">Int</a> <a href="#v:hash" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:id:Maybe:SingI:20" class="instance expander" onclick="toggleSection('i:id:Maybe:SingI:20')"></span> SingI (<a href="SafePrelude.html#t:Maybe">Maybe</a> a) (<a href="SafePrelude.html#v:Nothing">Nothing</a> a)</span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:id:Maybe:SingI:20" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:sing">sing</a> :: Sing (<a href="SafePrelude.html#v:Nothing">Nothing</a> a) a</p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="
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Unicode (or equivalently ISO/IEC 10646) characters (see
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<a href="http://www.unicode.org/">http://www.unicode.org/</a> for details). This set extends the ISO 8859-1
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(Latin-1) character set (the first 256 characters), which is itself an extension
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of the ASCII character set (the first 128 characters). A character literal in
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Haskell has type <code><a href="SafePrelude.html#t:Char">Char</a></code>.</p><p>To convert a <code><a href="SafePrelude.html#t:Char">Char</a></code> to or from the corresponding <code><a href="SafePrelude.html#t:Int">Int</a></code> value defined
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by Unicode, use <code><a href="../base-4.9.0.0/Prelude.html#v:toEnum">toEnum</a></code> and <code><a href="../base-4.9.0.0/Prelude.html#v:fromEnum">fromEnum</a></code> from the
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<code><a href="../base-4.9.0.0/Prelude.html#v:Enum">Enum</a></code> class respectively (or equivalently <code>ord</code> and <code>chr</code>).</p></div><div class="subs instances"><p id="control.i:Char" class="caption collapser" onclick="toggleSection('i:Char')">Instances</p><div id="section.i:Char" class="show"><table><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:id:Char:Bounded:1" class="instance expander" onclick="toggleSection('i:id:Char:Bounded:1')"></span> <a href="SafePrelude.html#t:Bounded">Bounded</a> <a href="SafePrelude.html#t:Char">Char</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:id:Char:Bounded:1" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:minBound">minBound</a> :: <a href="SafePrelude.html#t:Char">Char</a> <a href="#v:minBound" class="selflink">#</a></p><p class="src"><a href="#v:maxBound">maxBound</a> :: <a href="SafePrelude.html#t:Char">Char</a> <a href="#v:maxBound" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:id:Char:Enum:2" class="instance expander" onclick="toggleSection('i:id:Char:Enum:2')"></span> <a href="../base-4.9.0.0/Prelude.html#t:Enum">Enum</a> <a href="SafePrelude.html#t:Char">Char</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:id:Char:Enum:2" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:succ">succ</a> :: <a href="SafePrelude.html#t:Char">Char</a> -> <a href="SafePrelude.html#t:Char">Char</a> <a href="#v:succ" class="selflink">#</a></p><p class="src"><a href="#v:pred">pred</a> :: <a href="SafePrelude.html#t:Char">Char</a> -> <a href="SafePrelude.html#t:Char">Char</a> <a href="#v:pred" class="selflink">#</a></p><p class="src"><a href="#v:toEnum">toEnum</a> :: <a href="SafePrelude.html#t:Int">Int</a> -> <a href="SafePrelude.html#t:Char">Char</a> <a href="#v:toEnum" class="selflink">#</a></p><p class="src"><a href="#v:fromEnum">fromEnum</a> :: <a href="SafePrelude.html#t:Char">Char</a> -> <a href="SafePrelude.html#t:Int">Int</a> <a href="#v:fromEnum" class="selflink">#</a></p><p class="src"><a href="#v:enumFrom">enumFrom</a> :: <a href="SafePrelude.html#t:Char">Char</a> -> [<a href="SafePrelude.html#t:Char">Char</a>] <a href="#v:enumFrom" class="selflink">#</a></p><p class="src"><a href="#v:enumFromThen">enumFromThen</a> :: <a href="SafePrelude.html#t:Char">Char</a> -> <a href="SafePrelude.html#t:Char">Char</a> -> [<a href="SafePrelude.html#t:Char">Char</a>] <a href="#v:enumFromThen" class="selflink">#</a></p><p class="src"><a href="#v:enumFromTo">enumFromTo</a> :: <a href="SafePrelude.html#t:Char">Char</a> -> <a href="SafePrelude.html#t:Char">Char</a> -> [<a href="SafePrelude.html#t:Char">Char</a>] <a href="#v:enumFromTo" class="selflink">#</a></p><p class="src"><a href="#v:enumFromThenTo">enumFromThenTo</a> :: <a href="SafePrelude.html#t:Char">Char</a> -> <a href="SafePrelude.html#t:Char">Char</a> -> <a href="SafePrelude.html#t:Char">Char</a> -> [<a href="SafePrelude.html#t:Char">Char</a>] <a href="#v:enumFromThenTo" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:id:Char:Eq:3" class="instance expander" onclick="toggleSection('i:id:Char:Eq:3')"></span> <a href="SafePrelude.html#t:Eq">Eq</a> <a href="SafePrelude.html#t:Char">Char</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:id:Char:Eq:3" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:-61--61-">(==)</a> :: <a href="SafePrelude.html#t:Char">Char</a> -> <a href="SafePrelude.html#t:Char">Char</a> -> <a href="SafePrelude.html#t:Bool">Bool</a> <a href="#v:-61--61-" class="selflink">#</a></p><p class="src"><a href="#v:-47--61-">(/=)</a> :: <a href="SafePrelude.html#t:Char">Char</a> -> <a href="SafePrelude.
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does some I/O before returning a value of type <code>a</code>.</p><p>There is really only one way to "perform" an I/O action: bind it to
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<code>Main.main</code> in your program. When your program is run, the I/O will
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be performed. It isn't possible to perform I/O from an arbitrary
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function, unless that function is itself in the <code><a href="SafePrelude.html#t:IO">IO</a></code> monad and called
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at some point, directly or indirectly, from <code>Main.main</code>.</p><p><code><a href="SafePrelude.html#t:IO">IO</a></code> is a monad, so <code><a href="SafePrelude.html#t:IO">IO</a></code> actions can be combined using either the do-notation
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or the <code>>></code> and <code>>>=</code> operations from the <code>Monad</code> class.</p></div><div class="subs instances"><p id="control.i:IO" class="caption collapser" onclick="toggleSection('i:IO')">Instances</p><div id="section.i:IO" class="show"><table><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:id:IO:Monad:1" class="instance expander" onclick="toggleSection('i:id:IO:Monad:1')"></span> <a href="SafePrelude.html#t:Monad">Monad</a> <a href="SafePrelude.html#t:IO">IO</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:id:IO:Monad:1" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:-62--62--61-">(>>=)</a> :: <a href="SafePrelude.html#t:IO">IO</a> a -> (a -> <a href="SafePrelude.html#t:IO">IO</a> b) -> <a href="SafePrelude.html#t:IO">IO</a> b <a href="#v:-62--62--61-" class="selflink">#</a></p><p class="src"><a href="#v:-62--62-">(>>)</a> :: <a href="SafePrelude.html#t:IO">IO</a> a -> <a href="SafePrelude.html#t:IO">IO</a> b -> <a href="SafePrelude.html#t:IO">IO</a> b <a href="#v:-62--62-" class="selflink">#</a></p><p class="src"><a href="#v:return">return</a> :: a -> <a href="SafePrelude.html#t:IO">IO</a> a <a href="#v:return" class="selflink">#</a></p><p class="src"><a href="#v:fail">fail</a> :: <a href="SafePrelude.html#t:String">String</a> -> <a href="SafePrelude.html#t:IO">IO</a> a <a href="#v:fail" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:id:IO:Functor:2" class="instance expander" onclick="toggleSection('i:id:IO:Functor:2')"></span> <a href="SafePrelude.html#t:Functor">Functor</a> <a href="SafePrelude.html#t:IO">IO</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:id:IO:Functor:2" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:fmap">fmap</a> :: (a -> b) -> <a href="SafePrelude.html#t:IO">IO</a> a -> <a href="SafePrelude.html#t:IO">IO</a> b <a href="#v:fmap" class="selflink">#</a></p><p class="src"><a href="#v:-60--36-">(<$)</a> :: a -> <a href="SafePrelude.html#t:IO">IO</a> b -> <a href="SafePrelude.html#t:IO">IO</a> a <a href="#v:-60--36-" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:id:IO:Applicative:3" class="instance expander" onclick="toggleSection('i:id:IO:Applicative:3')"></span> <a href="SafePrelude.html#t:Applicative">Applicative</a> <a href="SafePrelude.html#t:IO">IO</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:id:IO:Applicative:3" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:pure">pure</a> :: a -> <a href="SafePrelude.html#t:IO">IO</a> a <a href="#v:pure" class="selflink">#</a></p><p class="src"><a href="#v:-60--42--62-">(<*>)</a> :: <a href="SafePrelude.html#t:IO">IO</a> (a -> b) -> <a href="SafePrelude.html#t:IO">IO</a> a -> <a href="SafePrelude.html#t:IO">IO</a> b <a href="#v:-60--42--62-" class="selflink">#</a></p><p class="src"><a href="#v:-42--62-">(*>)</a> :: <a href="SafePrelude.html#t:IO">IO</a> a -> <a href="SafePrelude.html#t:IO">IO</a> b -> <a href="SafePrelude.html#t:IO">IO</a> b <a href="#v:-42--62-" class="selflink">#</a></p><p class="src"><a href="#v:-60--42-">(<*)</a> :: <a href="SafePrelude.html#t:IO">IO</a> a -> <a href="SafePrelude.html#t:IO">IO</a> b -> <a href="SafePrelude.html#t:IO">IO</a> a <a href="#v:-60--42-" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:id:IO:MonadIO:4" class="instance expander" onclick="toggleSection('i:id:IO:MonadIO:4')"></span> <a href="SafePrelude.html#t:MonadIO">MonadIO</a> <a href="SafePrelude.html#t:IO">IO</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="
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type <code><code><a href="SafePrelude.html#t:Either">Either</a></code> a b</code> is either <code><code><a href="SafePrelude.html#v:Left">Left</a></code> a</code> or <code><code><a href="SafePrelude.html#v:Right">Right</a></code> b</code>.</p><p>The <code><a href="SafePrelude.html#t:Either">Either</a></code> type is sometimes used to represent a value which is
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either correct or an error; by convention, the <code><a href="SafePrelude.html#v:Left">Left</a></code> constructor is
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used to hold an error value and the <code><a href="SafePrelude.html#v:Right">Right</a></code> constructor is used to
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hold a correct value (mnemonic: "right" also means "correct").</p><h4 id="control.ch:noid:0" class="caption expander" onclick="toggleSection('ch:noid:0')">Examples</h4><div id="section.ch:noid:0" class="hide"><p>The type <code><code><a href="SafePrelude.html#t:Either">Either</a></code> <code><a href="SafePrelude.html#t:String">String</a></code> <code><a href="SafePrelude.html#t:Int">Int</a></code></code> is the type of values which can be either
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a <code><a href="SafePrelude.html#t:String">String</a></code> or an <code><a href="SafePrelude.html#t:Int">Int</a></code>. The <code><a href="SafePrelude.html#v:Left">Left</a></code> constructor can be used only on
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<code><a href="SafePrelude.html#t:String">String</a></code>s, and the <code><a href="SafePrelude.html#v:Right">Right</a></code> constructor can be used only on <code><a href="SafePrelude.html#t:Int">Int</a></code>s:</p><pre class="screen"><code class="prompt">>>> </code><strong class="userinput"><code>let s = Left "foo" :: Either String Int
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</code></strong><code class="prompt">>>> </code><strong class="userinput"><code>s
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</code></strong>Left "foo"
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<code class="prompt">>>> </code><strong class="userinput"><code>let n = Right 3 :: Either String Int
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</code></strong><code class="prompt">>>> </code><strong class="userinput"><code>n
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</code></strong>Right 3
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<code class="prompt">>>> </code><strong class="userinput"><code>:type s
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</code></strong>s :: Either String Int
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<code class="prompt">>>> </code><strong class="userinput"><code>:type n
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</code></strong>n :: Either String Int
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</pre><p>The <code><a href="SafePrelude.html#v:fmap">fmap</a></code> from our <code><a href="SafePrelude.html#t:Functor">Functor</a></code> instance will ignore <code><a href="SafePrelude.html#v:Left">Left</a></code> values, but
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will apply the supplied function to values contained in a <code><a href="SafePrelude.html#v:Right">Right</a></code>:</p><pre class="screen"><code class="prompt">>>> </code><strong class="userinput"><code>let s = Left "foo" :: Either String Int
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</code></strong><code class="prompt">>>> </code><strong class="userinput"><code>let n = Right 3 :: Either String Int
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</code></strong><code class="prompt">>>> </code><strong class="userinput"><code>fmap (*2) s
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</code></strong>Left "foo"
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<code class="prompt">>>> </code><strong class="userinput"><code>fmap (*2) n
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</code></strong>Right 6
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</pre><p>The <code><a href="SafePrelude.html#t:Monad">Monad</a></code> instance for <code><a href="SafePrelude.html#t:Either">Either</a></code> allows us to chain together multiple
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actions which may fail, and fail overall if any of the individual
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steps failed. First we'll write a function that can either parse an
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<code><a href="SafePrelude.html#t:Int">Int</a></code> from a <code><a href="SafePrelude.html#t:Char">Char</a></code>, or fail.</p><pre class="screen"><code class="prompt">>>> </code><strong class="userinput"><code>import Data.Char ( digitToInt, isDigit )
|
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|
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</code></strong><code class="prompt">>>> </code><strong class="userinput"><code>:{
|
||
|
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</code></strong> let parseEither :: Char -> Either String Int
|
||
|
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parseEither c
|
||
|
|
| isDigit c = Right (digitToInt c)
|
||
|
|
| otherwise = Left "parse error"
|
||
|
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<code class="prompt">>>> </code><strong class="userinput"><code>:}
|
||
|
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</code></strong></pre><p>The following should work, since both <code>'1'</code> and <code>'2'</code> can be
|
||
|
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parsed as <code><a href="SafePrelude.html#t:Int">Int</a></code>s.</p><pre class="screen"><code class="prompt">>>> </code><strong class="userinput"><code>:{
|
||
|
|
</code></strong> let parseMultiple :: Either String Int
|
||
|
|
parseMultiple = do
|
||
|
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x <- parseEither '1'
|
||
|
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y <- parseEither '2'
|
||
|
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return (x + y)
|
||
|
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<code class="prompt">>>> </code><strong class="userinput"><code>:}
|
||
|
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</code></strong></pre><pre class="screen"><code class="prompt">>>> </code><strong class="userinput"><code>parseMultiple
|
||
|
|
</code></strong>Right 3
|
||
|
|
</pre><p>But the following should fail overall, since the first operation where
|
||
|
|
we attempt to parse <code>'m'</code> as an <code><a href="SafePrelude.html#t:Int">Int</a></code> will fail:</p><pre class="screen"><code class="prompt">>>> </code><strong class="userinput"><code>:{
|
||
|
|
</code></strong> let parseMultiple :: Either String Int
|
||
|
|
parseMultiple = do
|
||
|
|
x <- parseEither 'm'
|
||
|
|
y <- parseEither '2'
|
||
|
|
return (x + y)
|
||
|
|
<code class="prompt">>>> </code><strong class="userinput"><code>:}
|
||
|
|
</code></strong></pre><pre class="screen"><code class="prompt">>>> </code><strong class="userinput"><code>parseMultiple
|
||
|
|
</code></strong>Left "parse error"
|
||
|
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</pre></div></div><div class="subs constructors"><p class="caption">Constructors</p><table><tr><td class="src"><a id="v:Left" class="def">Left</a> a</td><td class="doc empty"> </td></tr><tr><td class="src"><a id="v:Right" class="def">Right</a> b</td><td class="doc empty"> </td></tr></table></div><div class="subs instances"><p id="control.i:Either" class="caption collapser" onclick="toggleSection('i:Either')">Instances</p><div id="section.i:Either" class="show"><table><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:id:Either:Monad:1" class="instance expander" onclick="toggleSection('i:id:Either:Monad:1')"></span> <a href="SafePrelude.html#t:Monad">Monad</a> (<a href="SafePrelude.html#t:Either">Either</a> e)</span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:id:Either:Monad:1" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:-62--62--61-">(>>=)</a> :: <a href="SafePrelude.html#t:Either">Either</a> e a -> (a -> <a href="SafePrelude.html#t:Either">Either</a> e b) -> <a href="SafePrelude.html#t:Either">Either</a> e b <a href="#v:-62--62--61-" class="selflink">#</a></p><p class="src"><a href="#v:-62--62-">(>>)</a> :: <a href="SafePrelude.html#t:Either">Either</a> e a -> <a href="SafePrelude.html#t:Either">Either</a> e b -> <a href="SafePrelude.html#t:Either">Either</a> e b <a href="#v:-62--62-" class="selflink">#</a></p><p class="src"><a href="#v:return">return</a> :: a -> <a href="SafePrelude.html#t:Either">Either</a> e a <a href="#v:return" class="selflink">#</a></p><p class="src"><a href="#v:fail">fail</a> :: <a href="SafePrelude.html#t:String">String</a> -> <a href="SafePrelude.html#t:Either">Either</a> e a <a href="#v:fail" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:id:Either:Functor:2" class="instance expander" onclick="toggleSection('i:id:Either:Functor:2')"></span> <a href="SafePrelude.html#t:Functor">Functor</a> (<a href="SafePrelude.html#t:Either">Either</a> a)</span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:id:Either:Functor:2" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:fmap">fmap</a> :: (a -> b) -> <a href="SafePrelude.html#t:Either">Either</a> a a -> <a href="SafePrelude.html#t:Either">Either</a> a b <a href="#v:fmap" class="selflink">#</a></p><p class="src"><a href="#v:-60--36-">(<$)</a> :: a -> <a href="SafePrelude.html#t:Either">Either</a> a b -> <a href="SafePrelude.html#t:Either">Either</a> a a <a href="#v:-60--36-" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:id:Either:Applicative:3" class="instance expander" onclick="toggleSection('i:id:Either:Applicative:3')"></span> <a href="SafePrelude.html#t:Applicative">Applicative</a> (<a href="SafePrelude.html#t:Either">Either</a> e)</span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:id:Either:Applicative:3" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:pure">pure</a> :: a -> <a href="SafePrelude.html#t:Either">Either</a> e a <a href="#v:pure" class="selflink">#</a></p><p class="src"><a href="#v:-60--42--62-">(<*>)</a> :: <a href="SafePrelude.html#t:Either">Either</a> e (a -> b) -> <a href="SafePrelude.html#t:Either">Either</a> e a -> <a href="SafePrelude.html#t:Either">Either</a> e b <a href="#v:-60--42--62-" class="selflink">#</a></p><p class="src"><a href="#v:-42--62-">(*>)</a> :: <a href="SafePrelude.html#t:Either">Either</a> e a -> <a href="SafePrelude.html#t:Either">Either</a> e b -> <a href="SafePrelude.html#t:Either">Either</a> e b <a href="#v:-42--62-" class="selflink">#</a></p><p class="src"><a href="#v:-60--42-">(<*)</a> :: <a href="SafePrelude.html#t:Either">Either</a> e a -> <a href="Safe
|
||
|
|
efficient operations.</p><p>A <code><a href="SafePrelude.html#t:ByteString">ByteString</a></code> contains 8-bit bytes, or by using the operations from
|
||
|
|
<a href="../bytestring-0.10.8.1/Data-ByteString-Char8.html">Data.ByteString.Char8</a> it can be interpreted as containing 8-bit
|
||
|
|
characters.</p></div><div class="subs instances"><p id="control.i:ByteString" class="caption collapser" onclick="toggleSection('i:ByteString')">Instances</p><div id="section.i:ByteString" class="show"><table><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:id:ByteString:Eq:1" class="instance expander" onclick="toggleSection('i:id:ByteString:Eq:1')"></span> <a href="SafePrelude.html#t:Eq">Eq</a> <a href="SafePrelude.html#t:ByteString">ByteString</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:id:ByteString:Eq:1" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:-61--61-">(==)</a> :: <a href="SafePrelude.html#t:ByteString">ByteString</a> -> <a href="SafePrelude.html#t:ByteString">ByteString</a> -> <a href="SafePrelude.html#t:Bool">Bool</a> <a href="#v:-61--61-" class="selflink">#</a></p><p class="src"><a href="#v:-47--61-">(/=)</a> :: <a href="SafePrelude.html#t:ByteString">ByteString</a> -> <a href="SafePrelude.html#t:ByteString">ByteString</a> -> <a href="SafePrelude.html#t:Bool">Bool</a> <a href="#v:-47--61-" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:id:ByteString:Data:2" class="instance expander" onclick="toggleSection('i:id:ByteString:Data:2')"></span> <a href="../base-4.9.0.0/Data-Data.html#t:Data">Data</a> <a href="SafePrelude.html#t:ByteString">ByteString</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:id:ByteString:Data:2" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:gfoldl">gfoldl</a> :: (<span class="keyword">forall</span> d b. <a href="../base-4.9.0.0/Data-Data.html#t:Data">Data</a> d => c (d -> b) -> d -> c b) -> (<span class="keyword">forall</span> g. g -> c g) -> <a href="SafePrelude.html#t:ByteString">ByteString</a> -> c <a href="SafePrelude.html#t:ByteString">ByteString</a> <a href="#v:gfoldl" class="selflink">#</a></p><p class="src"><a href="#v:gunfold">gunfold</a> :: (<span class="keyword">forall</span> b r. <a href="../base-4.9.0.0/Data-Data.html#t:Data">Data</a> b => c (b -> r) -> c r) -> (<span class="keyword">forall</span> r. r -> c r) -> <a href="../base-4.9.0.0/Data-Data.html#t:Constr">Constr</a> -> c <a href="SafePrelude.html#t:ByteString">ByteString</a> <a href="#v:gunfold" class="selflink">#</a></p><p class="src"><a href="#v:toConstr">toConstr</a> :: <a href="SafePrelude.html#t:ByteString">ByteString</a> -> <a href="../base-4.9.0.0/Data-Data.html#t:Constr">Constr</a> <a href="#v:toConstr" class="selflink">#</a></p><p class="src"><a href="#v:dataTypeOf">dataTypeOf</a> :: <a href="SafePrelude.html#t:ByteString">ByteString</a> -> <a href="../base-4.9.0.0/Data-Data.html#t:DataType">DataType</a> <a href="#v:dataTypeOf" class="selflink">#</a></p><p class="src"><a href="#v:dataCast1">dataCast1</a> :: <a href="SafePrelude.html#t:Typeable">Typeable</a> (<a href="../base-4.9.0.0/Data-Kind.html#t:-42-">*</a> -> <a href="../base-4.9.0.0/Data-Kind.html#t:-42-">*</a>) t => (<span class="keyword">forall</span> d. <a href="../base-4.9.0.0/Data-Data.html#t:Data">Data</a> d => c (t d)) -> <a href="SafePrelude.html#t:Maybe">Maybe</a> (c <a href="SafePrelude.html#t:ByteString">ByteString</a>) <a href="#v:dataCast1" class="selflink">#</a></p><p class="src"><a href="#v:dataCast2">dataCast2</a> :: <a href="SafePrelude.html#t:Typeable">Typeable</a> (<a href="../base-4.9.0.0/Data-Kind.html#t:-42-">*</a> -> <a href="../base-4.9.0.0/Data-Kind.html#t:-42-">*</a> -> <a href="../base-4.9.0.0/Data-Kind.html#t:-42-">*</a>) t => (<span class="keyword">forall</span> d e. (<a href="../base-4.9.0.0/Data-Data.html#t:Data">Data</a> d, <a href="../base-4.9.0.0/Data-Data.html#t:Data">Data</a> e) => c (t d e)) -> <a href="SafePrelude.html#t:Maybe">Maybe</a> (c <a href="SafePrelude.html#t:ByteString">ByteString</a>) <a href="#v:dataCast2"
|
||
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each key can map to at most one value.</p></div><div class="subs instances"><p id="control.i:HashMap" class="caption collapser" onclick="toggleSection('i:HashMap')">Instances</p><div id="section.i:HashMap" class="show"><table><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:id:HashMap:Functor:1" class="instance expander" onclick="toggleSection('i:id:HashMap:Functor:1')"></span> <a href="SafePrelude.html#t:Functor">Functor</a> (<a href="SafePrelude.html#t:HashMap">HashMap</a> k)</span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:id:HashMap:Functor:1" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:fmap">fmap</a> :: (a -> b) -> <a href="SafePrelude.html#t:HashMap">HashMap</a> k a -> <a href="SafePrelude.html#t:HashMap">HashMap</a> k b <a href="#v:fmap" class="selflink">#</a></p><p class="src"><a href="#v:-60--36-">(<$)</a> :: a -> <a href="SafePrelude.html#t:HashMap">HashMap</a> k b -> <a href="SafePrelude.html#t:HashMap">HashMap</a> k a <a href="#v:-60--36-" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:id:HashMap:Foldable:2" class="instance expander" onclick="toggleSection('i:id:HashMap:Foldable:2')"></span> <a href="SafePrelude.html#t:Foldable">Foldable</a> (<a href="SafePrelude.html#t:HashMap">HashMap</a> k)</span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:id:HashMap:Foldable:2" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:fold">fold</a> :: <a href="SafePrelude.html#t:Monoid">Monoid</a> m => <a href="SafePrelude.html#t:HashMap">HashMap</a> k m -> m <a href="#v:fold" class="selflink">#</a></p><p class="src"><a href="#v:foldMap">foldMap</a> :: <a href="SafePrelude.html#t:Monoid">Monoid</a> m => (a -> m) -> <a href="SafePrelude.html#t:HashMap">HashMap</a> k a -> m <a href="#v:foldMap" class="selflink">#</a></p><p class="src"><a href="#v:foldr">foldr</a> :: (a -> b -> b) -> b -> <a href="SafePrelude.html#t:HashMap">HashMap</a> k a -> b <a href="#v:foldr" class="selflink">#</a></p><p class="src"><a href="#v:foldr-39-">foldr'</a> :: (a -> b -> b) -> b -> <a href="SafePrelude.html#t:HashMap">HashMap</a> k a -> b <a href="#v:foldr-39-" class="selflink">#</a></p><p class="src"><a href="#v:foldl">foldl</a> :: (b -> a -> b) -> b -> <a href="SafePrelude.html#t:HashMap">HashMap</a> k a -> b <a href="#v:foldl" class="selflink">#</a></p><p class="src"><a href="#v:foldl-39-">foldl'</a> :: (b -> a -> b) -> b -> <a href="SafePrelude.html#t:HashMap">HashMap</a> k a -> b <a href="#v:foldl-39-" class="selflink">#</a></p><p class="src"><a href="#v:foldr1">foldr1</a> :: (a -> a -> a) -> <a href="SafePrelude.html#t:HashMap">HashMap</a> k a -> a <a href="#v:foldr1" class="selflink">#</a></p><p class="src"><a href="#v:foldl1">foldl1</a> :: (a -> a -> a) -> <a href="SafePrelude.html#t:HashMap">HashMap</a> k a -> a <a href="#v:foldl1" class="selflink">#</a></p><p class="src"><a href="#v:toList">toList</a> :: <a href="SafePrelude.html#t:HashMap">HashMap</a> k a -> [a] <a href="#v:toList" class="selflink">#</a></p><p class="src"><a href="#v:null">null</a> :: <a href="SafePrelude.html#t:HashMap">HashMap</a> k a -> <a href="SafePrelude.html#t:Bool">Bool</a> <a href="#v:null" class="selflink">#</a></p><p class="src"><a href="#v:length">length</a> :: <a href="SafePrelude.html#t:HashMap">HashMap</a> k a -> <a href="SafePrelude.html#t:Int">Int</a> <a href="#v:length" class="selflink">#</a></p><p class="src"><a href="#v:elem">elem</a> :: <a href="SafePrelude.html#t:Eq">Eq</a> a => a -> <a href="SafePrelude.html#t:HashMap">HashMap</a> k a -> <a href="SafePrelude.html#t:Bool">Bool</a> <a href="#v:elem" class="selflink">#</a></p><p class="src"><a href="#v:maximum">maximum</a> :: <a href="SafePrelude.html#t:Ord">Ord</a> a =>
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<code><a href="SafePrelude.html#t:Identity">Identity</a></code> newtype if the <code><a href="SafePrelude.html#v:runIdentity">runIdentity</a></code> field were removed</p></td></tr><tr><td colspan="2"><div id="section.i:id:Identity:Read:18" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:readsPrec">readsPrec</a> :: <a href="SafePrelude.html#t:Int">Int</a> -> <a href="../base-4.9.0.0/Text-ParserCombinators-ReadP.html#t:ReadS">ReadS</a> (<a href="SafePrelude.html#t:Identity">Identity</a> a) <a href="#v:readsPrec" class="selflink">#</a></p><p class="src"><a href="#v:readList">readList</a> :: <a href="../base-4.9.0.0/Text-ParserCombinators-ReadP.html#t:ReadS">ReadS</a> [<a href="SafePrelude.html#t:Identity">Identity</a> a] <a href="#v:readList" class="selflink">#</a></p><p class="src"><a href="#v:readPrec">readPrec</a> :: <a href="../base-4.9.0.0/Text-ParserCombinators-ReadPrec.html#t:ReadPrec">ReadPrec</a> (<a href="SafePrelude.html#t:Identity">Identity</a> a) <a href="#v:readPrec" class="selflink">#</a></p><p class="src"><a href="#v:readListPrec">readListPrec</a> :: <a href="../base-4.9.0.0/Text-ParserCombinators-ReadPrec.html#t:ReadPrec">ReadPrec</a> [<a href="SafePrelude.html#t:Identity">Identity</a> a] <a href="#v:readListPrec" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:id:Identity:Real:19" class="instance expander" onclick="toggleSection('i:id:Identity:Real:19')"></span> <a href="SafePrelude.html#t:Real">Real</a> a => <a href="SafePrelude.html#t:Real">Real</a> (<a href="SafePrelude.html#t:Identity">Identity</a> a)</span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:id:Identity:Real:19" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:toRational">toRational</a> :: <a href="SafePrelude.html#t:Identity">Identity</a> a -> <a href="SafePrelude.html#t:Rational">Rational</a> <a href="#v:toRational" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:id:Identity:RealFloat:20" class="instance expander" onclick="toggleSection('i:id:Identity:RealFloat:20')"></span> <a href="SafePrelude.html#t:RealFloat">RealFloat</a> a => <a href="SafePrelude.html#t:RealFloat">RealFloat</a> (<a href="SafePrelude.html#t:Identity">Identity</a> a)</span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:id:Identity:RealFloat:20" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:floatRadix">floatRadix</a> :: <a href="SafePrelude.html#t:Identity">Identity</a> a -> <a href="SafePrelude.html#t:Integer">Integer</a> <a href="#v:floatRadix" class="selflink">#</a></p><p class="src"><a href="#v:floatDigits">floatDigits</a> :: <a href="SafePrelude.html#t:Identity">Identity</a> a -> <a href="SafePrelude.html#t:Int">Int</a> <a href="#v:floatDigits" class="selflink">#</a></p><p class="src"><a href="#v:floatRange">floatRange</a> :: <a href="SafePrelude.html#t:Identity">Identity</a> a -> (<a href="SafePrelude.html#t:Int">Int</a>, <a href="SafePrelude.html#t:Int">Int</a>) <a href="#v:floatRange" class="selflink">#</a></p><p class="src"><a href="#v:decodeFloat">decodeFloat</a> :: <a href="SafePrelude.html#t:Identity">Identity</a> a -> (<a href="SafePrelude.html#t:Integer">Integer</a>, <a href="SafePrelude.html#t:Int">Int</a>) <a href="#v:decodeFloat" class="selflink">#</a></p><p class="src"><a href="#v:encodeFloat">encodeFloat</a> :: <a href="SafePrelude.html#t:Integer">Integer</a> -> <a href="SafePrelude.html#t:Int">Int</a> -> <a href="SafePrelude.html#t:Identity">Identity</a> a <a href="#v:encodeFloat" class="selflink">#</a></p><p class="src"><a href="#v:exponent">exponent</a> :: <a href="SafePrelude.html#t:Identity">Identity</a> a -> <a href="SafePrelude.html#t:Int">Int</a> <a href="#v:exponent" class="selflink">#</a></p><p class="src"><a hre
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<code><a href="SafePrelude.html#t:Identity">Identity</a></code> newtype if the <code><a href="SafePrelude.html#v:runIdentity">runIdentity</a></code> field were removed</p></td></tr><tr><td colspan="2"><div id="section.i:id:Identity:Show:22" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:showsPrec">showsPrec</a> :: <a href="SafePrelude.html#t:Int">Int</a> -> <a href="SafePrelude.html#t:Identity">Identity</a> a -> <a href="../base-4.9.0.0/Text-Show.html#t:ShowS">ShowS</a> <a href="#v:showsPrec" class="selflink">#</a></p><p class="src"><a href="#v:show">show</a> :: <a href="SafePrelude.html#t:Identity">Identity</a> a -> <a href="SafePrelude.html#t:String">String</a> <a href="#v:show" class="selflink">#</a></p><p class="src"><a href="#v:showList">showList</a> :: [<a href="SafePrelude.html#t:Identity">Identity</a> a] -> <a href="../base-4.9.0.0/Text-Show.html#t:ShowS">ShowS</a> <a href="#v:showList" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:id:Identity:Ix:23" class="instance expander" onclick="toggleSection('i:id:Identity:Ix:23')"></span> <a href="../base-4.9.0.0/Data-Ix.html#t:Ix">Ix</a> a => <a href="../base-4.9.0.0/Data-Ix.html#t:Ix">Ix</a> (<a href="SafePrelude.html#t:Identity">Identity</a> a)</span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:id:Identity:Ix:23" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:range">range</a> :: (<a href="SafePrelude.html#t:Identity">Identity</a> a, <a href="SafePrelude.html#t:Identity">Identity</a> a) -> [<a href="SafePrelude.html#t:Identity">Identity</a> a] <a href="#v:range" class="selflink">#</a></p><p class="src"><a href="#v:index">index</a> :: (<a href="SafePrelude.html#t:Identity">Identity</a> a, <a href="SafePrelude.html#t:Identity">Identity</a> a) -> <a href="SafePrelude.html#t:Identity">Identity</a> a -> <a href="SafePrelude.html#t:Int">Int</a> <a href="#v:index" class="selflink">#</a></p><p class="src"><a href="#v:unsafeIndex">unsafeIndex</a> :: (<a href="SafePrelude.html#t:Identity">Identity</a> a, <a href="SafePrelude.html#t:Identity">Identity</a> a) -> <a href="SafePrelude.html#t:Identity">Identity</a> a -> <a href="SafePrelude.html#t:Int">Int</a></p><p class="src"><a href="#v:inRange">inRange</a> :: (<a href="SafePrelude.html#t:Identity">Identity</a> a, <a href="SafePrelude.html#t:Identity">Identity</a> a) -> <a href="SafePrelude.html#t:Identity">Identity</a> a -> <a href="SafePrelude.html#t:Bool">Bool</a> <a href="#v:inRange" class="selflink">#</a></p><p class="src"><a href="#v:rangeSize">rangeSize</a> :: (<a href="SafePrelude.html#t:Identity">Identity</a> a, <a href="SafePrelude.html#t:Identity">Identity</a> a) -> <a href="SafePrelude.html#t:Int">Int</a> <a href="#v:rangeSize" class="selflink">#</a></p><p class="src"><a href="#v:unsafeRangeSize">unsafeRangeSize</a> :: (<a href="SafePrelude.html#t:Identity">Identity</a> a, <a href="SafePrelude.html#t:Identity">Identity</a> a) -> <a href="SafePrelude.html#t:Int">Int</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:id:Identity:IsString:24" class="instance expander" onclick="toggleSection('i:id:Identity:IsString:24')"></span> <a href="SafePrelude.html#t:IsString">IsString</a> a => <a href="SafePrelude.html#t:IsString">IsString</a> (<a href="SafePrelude.html#t:Identity">Identity</a> a)</span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:id:Identity:IsString:24" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:fromString">fromString</a> :: <a href="SafePrelude.html#t:String">String</a> -> <a href="SafePrelude.html#t:Identity">Identity</a> a <a href="#v:fromString" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:id:Identity:Gen
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When an exception of type <code>e</code> is thrown, behind the scenes it is
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encapsulated in a <code>SomeException</code>.</p></div><div class="subs constructors"><p class="caption">Constructors</p><table><tr><td class="src"><a id="v:SomeException" class="def">SomeException</a> :: <a href="SafePrelude.html#t:SomeException">SomeException</a></td><td class="doc empty"> </td></tr></table></div><div class="subs instances"><p id="control.i:SomeException" class="caption collapser" onclick="toggleSection('i:SomeException')">Instances</p><div id="section.i:SomeException" class="show"><table><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:id:SomeException:Show:1" class="instance expander" onclick="toggleSection('i:id:SomeException:Show:1')"></span> <a href="SafePrelude.html#t:Show">Show</a> <a href="SafePrelude.html#t:SomeException">SomeException</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:id:SomeException:Show:1" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:showsPrec">showsPrec</a> :: <a href="SafePrelude.html#t:Int">Int</a> -> <a href="SafePrelude.html#t:SomeException">SomeException</a> -> <a href="../base-4.9.0.0/Text-Show.html#t:ShowS">ShowS</a> <a href="#v:showsPrec" class="selflink">#</a></p><p class="src"><a href="#v:show">show</a> :: <a href="SafePrelude.html#t:SomeException">SomeException</a> -> <a href="SafePrelude.html#t:String">String</a> <a href="#v:show" class="selflink">#</a></p><p class="src"><a href="#v:showList">showList</a> :: [<a href="SafePrelude.html#t:SomeException">SomeException</a>] -> <a href="../base-4.9.0.0/Text-Show.html#t:ShowS">ShowS</a> <a href="#v:showList" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:id:SomeException:Exception:2" class="instance expander" onclick="toggleSection('i:id:SomeException:Exception:2')"></span> <a href="SafePrelude.html#t:Exception">Exception</a> <a href="SafePrelude.html#t:SomeException">SomeException</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:id:SomeException:Exception:2" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:toException">toException</a> :: <a href="SafePrelude.html#t:SomeException">SomeException</a> -> <a href="SafePrelude.html#t:SomeException">SomeException</a> <a href="#v:toException" class="selflink">#</a></p><p class="src"><a href="#v:fromException">fromException</a> :: <a href="SafePrelude.html#t:SomeException">SomeException</a> -> <a href="SafePrelude.html#t:Maybe">Maybe</a> <a href="SafePrelude.html#t:SomeException">SomeException</a> <a href="#v:fromException" class="selflink">#</a></p><p class="src"><a href="#v:displayException">displayException</a> :: <a href="SafePrelude.html#t:SomeException">SomeException</a> -> <a href="SafePrelude.html#t:String">String</a> <a href="#v:displayException" class="selflink">#</a></p></div></div></td></tr></table></div></div></div><div class="top"><p class="src"><span class="keyword">data</span> <a id="t:SomeAsyncException" class="def">SomeAsyncException</a> :: <a href="../base-4.9.0.0/Data-Kind.html#t:-42-">*</a> <span class="keyword">where</span> <a href="#t:SomeAsyncException" class="selflink">#</a></p><div class="doc"><p>Superclass for asynchronous exceptions.</p><p><em>Since: 4.7.0.0</em></p></div><div class="subs constructors"><p class="caption">Constructors</p><table><tr><td class="src"><a id="v:SomeAsyncException" class="def">SomeAsyncException</a> :: <a href="SafePrelude.html#t:SomeAsyncException">SomeAsyncException</a></td><td class="doc empty"> </td></tr></table></div><div class="subs instances"><p id="control.i:SomeAsyncException" class="caption collapser" onclick="toggleSection('i:SomeAsyncException')">Instances</p><div id="section.i:SomeAsyncException" class="show"><table><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:id:SomeAsyncException:Show:1" class="instance expander" onclick="toggleSection('i:id:Some
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of type <code><a href="SafePrelude.html#t:String">String</a></code>.</p></div></div><div class="top"><p class="src"><span class="keyword">type</span> <a id="t:FilePath" class="def">FilePath</a> = <a href="SafePrelude.html#t:String">String</a> <a href="#t:FilePath" class="selflink">#</a></p><div class="doc"><p>File and directory names are values of type <code><a href="SafePrelude.html#t:String">String</a></code>, whose precise
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meaning is operating system dependent. Files can be opened, yielding a
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handle which can then be used to operate on the contents of that file.</p></div></div><h2 id="g:2">Numbers</h2><div class="top"><p class="src"><span class="keyword">data</span> <a id="t:Word" class="def">Word</a> :: <a href="../base-4.9.0.0/Data-Kind.html#t:-42-">*</a> <a href="#t:Word" class="selflink">#</a></p><div class="doc"><p>A <code><a href="SafePrelude.html#t:Word">Word</a></code> is an unsigned integral type, with the same size as <code><a href="SafePrelude.html#t:Int">Int</a></code>.</p></div><div class="subs instances"><p id="control.i:Word" class="caption collapser" onclick="toggleSection('i:Word')">Instances</p><div id="section.i:Word" class="show"><table><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:id:Word:Bounded:1" class="instance expander" onclick="toggleSection('i:id:Word:Bounded:1')"></span> <a href="SafePrelude.html#t:Bounded">Bounded</a> <a href="SafePrelude.html#t:Word">Word</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:id:Word:Bounded:1" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:minBound">minBound</a> :: <a href="SafePrelude.html#t:Word">Word</a> <a href="#v:minBound" class="selflink">#</a></p><p class="src"><a href="#v:maxBound">maxBound</a> :: <a href="SafePrelude.html#t:Word">Word</a> <a href="#v:maxBound" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:id:Word:Enum:2" class="instance expander" onclick="toggleSection('i:id:Word:Enum:2')"></span> <a href="../base-4.9.0.0/Prelude.html#t:Enum">Enum</a> <a href="SafePrelude.html#t:Word">Word</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:id:Word:Enum:2" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:succ">succ</a> :: <a href="SafePrelude.html#t:Word">Word</a> -> <a href="SafePrelude.html#t:Word">Word</a> <a href="#v:succ" class="selflink">#</a></p><p class="src"><a href="#v:pred">pred</a> :: <a href="SafePrelude.html#t:Word">Word</a> -> <a href="SafePrelude.html#t:Word">Word</a> <a href="#v:pred" class="selflink">#</a></p><p class="src"><a href="#v:toEnum">toEnum</a> :: <a href="SafePrelude.html#t:Int">Int</a> -> <a href="SafePrelude.html#t:Word">Word</a> <a href="#v:toEnum" class="selflink">#</a></p><p class="src"><a href="#v:fromEnum">fromEnum</a> :: <a href="SafePrelude.html#t:Word">Word</a> -> <a href="SafePrelude.html#t:Int">Int</a> <a href="#v:fromEnum" class="selflink">#</a></p><p class="src"><a href="#v:enumFrom">enumFrom</a> :: <a href="SafePrelude.html#t:Word">Word</a> -> [<a href="SafePrelude.html#t:Word">Word</a>] <a href="#v:enumFrom" class="selflink">#</a></p><p class="src"><a href="#v:enumFromThen">enumFromThen</a> :: <a href="SafePrelude.html#t:Word">Word</a> -> <a href="SafePrelude.html#t:Word">Word</a> -> [<a href="SafePrelude.html#t:Word">Word</a>] <a href="#v:enumFromThen" class="selflink">#</a></p><p class="src"><a href="#v:enumFromTo">enumFromTo</a> :: <a href="SafePrelude.html#t:Word">Word</a> -> <a href="SafePrelude.html#t:Word">Word</a> -> [<a href="SafePrelude.html#t:Word">Word</a>] <a href="#v:enumFromTo" class="selflink">#</a></p><p class="src"><a href="#v:enumFromThenTo">enumFromThenTo</a> :: <a href="SafePrelude.html#t:Word">Word</a> -> <a href="SafePrelude.html#t:Word">Word</a> -> <a href="SafePrelude.html#t:Word">Word</a> -> [<a href="SafePrelude.html#t:Word">Word</a>] <a href="#v:enumFromThenTo" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:id:Word:Eq:3" class="instance expander" onclick="toggleSection('i:id:Word:Eq:3')"></span> <a href="SafePrelude.html#t:Eq">Eq</a> <a href="SafePrelude.html#t:Word">Word</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:id:Word:Eq:3" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><
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The exact range for a given implementation can be determined by using
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<code><a href="../base-4.9.0.0/Prelude.html#v:minBound">minBound</a></code> and <code><a href="../base-4.9.0.0/Prelude.html#v:maxBound">maxBound</a></code> from the <code><a href="../base-4.9.0.0/Prelude.html#v:Bounded">Bounded</a></code> class.</p></div><div class="subs instances"><p id="control.i:Int" class="caption collapser" onclick="toggleSection('i:Int')">Instances</p><div id="section.i:Int" class="show"><table><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:id:Int:Bounded:1" class="instance expander" onclick="toggleSection('i:id:Int:Bounded:1')"></span> <a href="SafePrelude.html#t:Bounded">Bounded</a> <a href="SafePrelude.html#t:Int">Int</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:id:Int:Bounded:1" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:minBound">minBound</a> :: <a href="SafePrelude.html#t:Int">Int</a> <a href="#v:minBound" class="selflink">#</a></p><p class="src"><a href="#v:maxBound">maxBound</a> :: <a href="SafePrelude.html#t:Int">Int</a> <a href="#v:maxBound" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:id:Int:Enum:2" class="instance expander" onclick="toggleSection('i:id:Int:Enum:2')"></span> <a href="../base-4.9.0.0/Prelude.html#t:Enum">Enum</a> <a href="SafePrelude.html#t:Int">Int</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:id:Int:Enum:2" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:succ">succ</a> :: <a href="SafePrelude.html#t:Int">Int</a> -> <a href="SafePrelude.html#t:Int">Int</a> <a href="#v:succ" class="selflink">#</a></p><p class="src"><a href="#v:pred">pred</a> :: <a href="SafePrelude.html#t:Int">Int</a> -> <a href="SafePrelude.html#t:Int">Int</a> <a href="#v:pred" class="selflink">#</a></p><p class="src"><a href="#v:toEnum">toEnum</a> :: <a href="SafePrelude.html#t:Int">Int</a> -> <a href="SafePrelude.html#t:Int">Int</a> <a href="#v:toEnum" class="selflink">#</a></p><p class="src"><a href="#v:fromEnum">fromEnum</a> :: <a href="SafePrelude.html#t:Int">Int</a> -> <a href="SafePrelude.html#t:Int">Int</a> <a href="#v:fromEnum" class="selflink">#</a></p><p class="src"><a href="#v:enumFrom">enumFrom</a> :: <a href="SafePrelude.html#t:Int">Int</a> -> [<a href="SafePrelude.html#t:Int">Int</a>] <a href="#v:enumFrom" class="selflink">#</a></p><p class="src"><a href="#v:enumFromThen">enumFromThen</a> :: <a href="SafePrelude.html#t:Int">Int</a> -> <a href="SafePrelude.html#t:Int">Int</a> -> [<a href="SafePrelude.html#t:Int">Int</a>] <a href="#v:enumFromThen" class="selflink">#</a></p><p class="src"><a href="#v:enumFromTo">enumFromTo</a> :: <a href="SafePrelude.html#t:Int">Int</a> -> <a href="SafePrelude.html#t:Int">Int</a> -> [<a href="SafePrelude.html#t:Int">Int</a>] <a href="#v:enumFromTo" class="selflink">#</a></p><p class="src"><a href="#v:enumFromThenTo">enumFromThenTo</a> :: <a href="SafePrelude.html#t:Int">Int</a> -> <a href="SafePrelude.html#t:Int">Int</a> -> <a href="SafePrelude.html#t:Int">Int</a> -> [<a href="SafePrelude.html#t:Int">Int</a>] <a href="#v:enumFromThenTo" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:id:Int:Eq:3" class="instance expander" onclick="toggleSection('i:id:Int:Eq:3')"></span> <a href="SafePrelude.html#t:Eq">Eq</a> <a href="SafePrelude.html#t:Int">Int</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:id:Int:Eq:3" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:-61--61-">(==)</a> :: <a href="SafePrelude.html#t:Int">Int</a> -> <a href="SafePrelude.html#t:Int">Int</a> -> <a href="SafePrelude.html#t:Bool">Bool</a> <a href="#v:-61--61-" class="selflink">#</a></p><p class="src"><a href="#v:-47--61-">(/=)</a> :: <a href="SafePrelude.html#t:I
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two <code><a href="SafePrelude.html#t:Integer">Integer</a></code> values. A rational number may be constructed using
|
||
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the <code><a href="../base-4.9.0.0/Data-Ratio.html#v:-37-">%</a></code> operator.</p></div></div><div class="top"><p class="src"><span class="keyword">data</span> <a id="t:Float" class="def">Float</a> :: <a href="../base-4.9.0.0/Data-Kind.html#t:-42-">*</a> <a href="#t:Float" class="selflink">#</a></p><div class="doc"><p>Single-precision floating point numbers.
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It is desirable that this type be at least equal in range and precision
|
||
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to the IEEE single-precision type.</p></div><div class="subs instances"><p id="control.i:Float" class="caption collapser" onclick="toggleSection('i:Float')">Instances</p><div id="section.i:Float" class="show"><table><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:id:Float:Eq:1" class="instance expander" onclick="toggleSection('i:id:Float:Eq:1')"></span> <a href="SafePrelude.html#t:Eq">Eq</a> <a href="SafePrelude.html#t:Float">Float</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:id:Float:Eq:1" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:-61--61-">(==)</a> :: <a href="SafePrelude.html#t:Float">Float</a> -> <a href="SafePrelude.html#t:Float">Float</a> -> <a href="SafePrelude.html#t:Bool">Bool</a> <a href="#v:-61--61-" class="selflink">#</a></p><p class="src"><a href="#v:-47--61-">(/=)</a> :: <a href="SafePrelude.html#t:Float">Float</a> -> <a href="SafePrelude.html#t:Float">Float</a> -> <a href="SafePrelude.html#t:Bool">Bool</a> <a href="#v:-47--61-" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:id:Float:Floating:2" class="instance expander" onclick="toggleSection('i:id:Float:Floating:2')"></span> <a href="SafePrelude.html#t:Floating">Floating</a> <a href="SafePrelude.html#t:Float">Float</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:id:Float:Floating:2" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:pi">pi</a> :: <a href="SafePrelude.html#t:Float">Float</a> <a href="#v:pi" class="selflink">#</a></p><p class="src"><a href="#v:exp">exp</a> :: <a href="SafePrelude.html#t:Float">Float</a> -> <a href="SafePrelude.html#t:Float">Float</a> <a href="#v:exp" class="selflink">#</a></p><p class="src"><a href="#v:log">log</a> :: <a href="SafePrelude.html#t:Float">Float</a> -> <a href="SafePrelude.html#t:Float">Float</a> <a href="#v:log" class="selflink">#</a></p><p class="src"><a href="#v:sqrt">sqrt</a> :: <a href="SafePrelude.html#t:Float">Float</a> -> <a href="SafePrelude.html#t:Float">Float</a> <a href="#v:sqrt" class="selflink">#</a></p><p class="src"><a href="#v:-42--42-">(**)</a> :: <a href="SafePrelude.html#t:Float">Float</a> -> <a href="SafePrelude.html#t:Float">Float</a> -> <a href="SafePrelude.html#t:Float">Float</a> <a href="#v:-42--42-" class="selflink">#</a></p><p class="src"><a href="#v:logBase">logBase</a> :: <a href="SafePrelude.html#t:Float">Float</a> -> <a href="SafePrelude.html#t:Float">Float</a> -> <a href="SafePrelude.html#t:Float">Float</a> <a href="#v:logBase" class="selflink">#</a></p><p class="src"><a href="#v:sin">sin</a> :: <a href="SafePrelude.html#t:Float">Float</a> -> <a href="SafePrelude.html#t:Float">Float</a> <a href="#v:sin" class="selflink">#</a></p><p class="src"><a href="#v:cos">cos</a> :: <a href="SafePrelude.html#t:Float">Float</a> -> <a href="SafePrelude.html#t:Float">Float</a> <a href="#v:cos" class="selflink">#</a></p><p class="src"><a href="#v:tan">tan</a> :: <a href="SafePrelude.html#t:Float">Float</a> -> <a href="SafePrelude.html#t:Float">Float</a> <a href="#v:tan" class="selflink">#</a></p><p class="src"><a href="#v:asin">asin</a> :: <a href="SafePrelude.html#t:Float">Float</a> -> <a href="SafePrelude.html#t:Float">Float</a> <a href="#v:asin" class="selflink">#</a></p><p class="src"><a href="#v:acos">acos</a> :: <a href="SafePrelude.html#t:Float">Float</a> -> <a href="SafePrelude.html#t:Float">Float</a> <a href="#v:acos" class="selflink">#</a></p><p class="src"><a href="#v:atan">atan</a> :: <a href="SafePrelude.html#t:Float">Float</a> -> <a href="SafePrelude.html#t:Float">Float</a> <a href="#v:atan" class="selflink">#</a></p><p class="src"><a href="#v:sinh">sinh</a> :: <a href="SafePrelude.html#t:Float">Float</a> -> <a href="SafePrelude.html#t:Float">Float</a> <a href="#v:sinh" class="selflink">#</a></p><p class="src"><a href
|
||
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It is desirable that this type be at least equal in range and precision
|
||
|
|
to the IEEE double-precision type.</p></div><div class="subs instances"><p id="control.i:Double" class="caption collapser" onclick="toggleSection('i:Double')">Instances</p><div id="section.i:Double" class="show"><table><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:id:Double:Eq:1" class="instance expander" onclick="toggleSection('i:id:Double:Eq:1')"></span> <a href="SafePrelude.html#t:Eq">Eq</a> <a href="SafePrelude.html#t:Double">Double</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:id:Double:Eq:1" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:-61--61-">(==)</a> :: <a href="SafePrelude.html#t:Double">Double</a> -> <a href="SafePrelude.html#t:Double">Double</a> -> <a href="SafePrelude.html#t:Bool">Bool</a> <a href="#v:-61--61-" class="selflink">#</a></p><p class="src"><a href="#v:-47--61-">(/=)</a> :: <a href="SafePrelude.html#t:Double">Double</a> -> <a href="SafePrelude.html#t:Double">Double</a> -> <a href="SafePrelude.html#t:Bool">Bool</a> <a href="#v:-47--61-" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:id:Double:Floating:2" class="instance expander" onclick="toggleSection('i:id:Double:Floating:2')"></span> <a href="SafePrelude.html#t:Floating">Floating</a> <a href="SafePrelude.html#t:Double">Double</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:id:Double:Floating:2" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:pi">pi</a> :: <a href="SafePrelude.html#t:Double">Double</a> <a href="#v:pi" class="selflink">#</a></p><p class="src"><a href="#v:exp">exp</a> :: <a href="SafePrelude.html#t:Double">Double</a> -> <a href="SafePrelude.html#t:Double">Double</a> <a href="#v:exp" class="selflink">#</a></p><p class="src"><a href="#v:log">log</a> :: <a href="SafePrelude.html#t:Double">Double</a> -> <a href="SafePrelude.html#t:Double">Double</a> <a href="#v:log" class="selflink">#</a></p><p class="src"><a href="#v:sqrt">sqrt</a> :: <a href="SafePrelude.html#t:Double">Double</a> -> <a href="SafePrelude.html#t:Double">Double</a> <a href="#v:sqrt" class="selflink">#</a></p><p class="src"><a href="#v:-42--42-">(**)</a> :: <a href="SafePrelude.html#t:Double">Double</a> -> <a href="SafePrelude.html#t:Double">Double</a> -> <a href="SafePrelude.html#t:Double">Double</a> <a href="#v:-42--42-" class="selflink">#</a></p><p class="src"><a href="#v:logBase">logBase</a> :: <a href="SafePrelude.html#t:Double">Double</a> -> <a href="SafePrelude.html#t:Double">Double</a> -> <a href="SafePrelude.html#t:Double">Double</a> <a href="#v:logBase" class="selflink">#</a></p><p class="src"><a href="#v:sin">sin</a> :: <a href="SafePrelude.html#t:Double">Double</a> -> <a href="SafePrelude.html#t:Double">Double</a> <a href="#v:sin" class="selflink">#</a></p><p class="src"><a href="#v:cos">cos</a> :: <a href="SafePrelude.html#t:Double">Double</a> -> <a href="SafePrelude.html#t:Double">Double</a> <a href="#v:cos" class="selflink">#</a></p><p class="src"><a href="#v:tan">tan</a> :: <a href="SafePrelude.html#t:Double">Double</a> -> <a href="SafePrelude.html#t:Double">Double</a> <a href="#v:tan" class="selflink">#</a></p><p class="src"><a href="#v:asin">asin</a> :: <a href="SafePrelude.html#t:Double">Double</a> -> <a href="SafePrelude.html#t:Double">Double</a> <a href="#v:asin" class="selflink">#</a></p><p class="src"><a href="#v:acos">acos</a> :: <a href="SafePrelude.html#t:Double">Double</a> -> <a href="SafePrelude.html#t:Double">Double</a> <a href="#v:acos" class="selflink">#</a></p><p class="src"><a href="#v:atan">atan</a> :: <a href="SafePrelude.html#t:Double">Double</a> -> <a href="SafePrelude.html#t:Double">Double</a> <a href="#v:atan" class="selflink">#</a></p><p class="src"><a href="#v:sinh">sinh</a> :: <a href="SafePrelude.html#t:Double">Double</a> -> <a href="SafePrelude.html#t:Double">Do
|
||
|
|
datatype whose constituent types are in <code><a href="SafePrelude.html#t:Ord">Ord</a></code>. The declared order
|
||
|
|
of the constructors in the data declaration determines the ordering
|
||
|
|
in derived <code><a href="SafePrelude.html#t:Ord">Ord</a></code> instances. The <code><a href="SafePrelude.html#t:Ordering">Ordering</a></code> datatype allows a single
|
||
|
|
comparison to determine the precise ordering of two objects.</p><p>Minimal complete definition: either <code><a href="SafePrelude.html#v:compare">compare</a></code> or <code><a href="SafePrelude.html#v:-60--61-"><=</a></code>.
|
||
|
|
Using <code><a href="SafePrelude.html#v:compare">compare</a></code> can be more efficient for complex types.</p></div><div class="subs minimal"><p class="caption">Minimal complete definition</p><p class="src"><a href="SafePrelude.html#v:compare">compare</a> | <a href="SafePrelude.html#v:-60--61-">(<=)</a></p></div><div class="subs instances"><p id="control.i:Ord" class="caption collapser" onclick="toggleSection('i:Ord')">Instances</p><div id="section.i:Ord" class="show"><table><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Ord:Ord:1" class="instance expander" onclick="toggleSection('i:ic:Ord:Ord:1')"></span> <a href="SafePrelude.html#t:Ord">Ord</a> <a href="SafePrelude.html#t:Bool">Bool</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:Ord:Ord:1" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:compare">compare</a> :: <a href="SafePrelude.html#t:Bool">Bool</a> -> <a href="SafePrelude.html#t:Bool">Bool</a> -> <a href="SafePrelude.html#t:Ordering">Ordering</a> <a href="#v:compare" class="selflink">#</a></p><p class="src"><a href="#v:-60-">(<)</a> :: <a href="SafePrelude.html#t:Bool">Bool</a> -> <a href="SafePrelude.html#t:Bool">Bool</a> -> <a href="SafePrelude.html#t:Bool">Bool</a> <a href="#v:-60-" class="selflink">#</a></p><p class="src"><a href="#v:-60--61-">(<=)</a> :: <a href="SafePrelude.html#t:Bool">Bool</a> -> <a href="SafePrelude.html#t:Bool">Bool</a> -> <a href="SafePrelude.html#t:Bool">Bool</a> <a href="#v:-60--61-" class="selflink">#</a></p><p class="src"><a href="#v:-62-">(>)</a> :: <a href="SafePrelude.html#t:Bool">Bool</a> -> <a href="SafePrelude.html#t:Bool">Bool</a> -> <a href="SafePrelude.html#t:Bool">Bool</a> <a href="#v:-62-" class="selflink">#</a></p><p class="src"><a href="#v:-62--61-">(>=)</a> :: <a href="SafePrelude.html#t:Bool">Bool</a> -> <a href="SafePrelude.html#t:Bool">Bool</a> -> <a href="SafePrelude.html#t:Bool">Bool</a> <a href="#v:-62--61-" class="selflink">#</a></p><p class="src"><a href="#v:max">max</a> :: <a href="SafePrelude.html#t:Bool">Bool</a> -> <a href="SafePrelude.html#t:Bool">Bool</a> -> <a href="SafePrelude.html#t:Bool">Bool</a> <a href="#v:max" class="selflink">#</a></p><p class="src"><a href="#v:min">min</a> :: <a href="SafePrelude.html#t:Bool">Bool</a> -> <a href="SafePrelude.html#t:Bool">Bool</a> -> <a href="SafePrelude.html#t:Bool">Bool</a> <a href="#v:min" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Ord:Ord:2" class="instance expander" onclick="toggleSection('i:ic:Ord:Ord:2')"></span> <a href="SafePrelude.html#t:Ord">Ord</a> <a href="SafePrelude.html#t:Char">Char</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:Ord:Ord:2" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:compare">compare</a> :: <a href="SafePrelude.html#t:Char">Char</a> -> <a href="SafePrelude.html#t:Char">Char</a> -> <a href="SafePrelude.html#t:Ordering">Ordering</a> <a href="#v:compare" class="selflink">#</a></p><p class="src"><a href="#v:-60-">(<)</a> :: <a href="SafePrelude.html#t:Char">Char</a> -> <a href="SafePrelude.html#t:Char">Char</a> -> <a href="SafePrelude.html#t:Bool">Bool</a> <a href="#v:-60-" class="selflink">#</a></p><p class="src"><a href="#v:-60--61-">(<=)</a> :: <a href="SafePrelude.html#t:Char">Char</a> -> <a href="SafePrelude.html#t:Char">Char</a> -> <a href="SafePrelude.html#t:Bool">Bool</a> <a href="#v:-60--61-" class="selflink">#</a></p><p class="src"><a href="#v:-62-">(>)</a> :: <a href="SafePrelude.html#t:Char">Char</a> -> <a href="SafePrelude.html#t:Char">Char</a> -> <a href="SafePrelude.html#t:Bool">Bool</a> <a href="#v:-62-" class="selflink">#</a></p><p class="src"><a href="#v:-62--61-">(>=)</a> :: <a href="SafePrelude.html#t:Char">Char</a> -> <a href="SafePrelude.html
|
||
|
|
All the basic datatypes exported by the <a href="../base-4.9.0.0/Prelude.html">Prelude</a> are instances of <code><a href="SafePrelude.html#t:Eq">Eq</a></code>,
|
||
|
|
and <code><a href="SafePrelude.html#t:Eq">Eq</a></code> may be derived for any datatype whose constituents are also
|
||
|
|
instances of <code><a href="SafePrelude.html#t:Eq">Eq</a></code>.</p><p>Minimal complete definition: either <code><a href="SafePrelude.html#v:-61--61-">==</a></code> or <code><a href="SafePrelude.html#v:-47--61-">/=</a></code>.</p></div><div class="subs minimal"><p class="caption">Minimal complete definition</p><p class="src"><a href="SafePrelude.html#v:-61--61-">(==)</a> | <a href="SafePrelude.html#v:-47--61-">(/=)</a></p></div><div class="subs instances"><p id="control.i:Eq" class="caption collapser" onclick="toggleSection('i:Eq')">Instances</p><div id="section.i:Eq" class="show"><table><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Eq:Eq:1" class="instance expander" onclick="toggleSection('i:ic:Eq:Eq:1')"></span> <a href="SafePrelude.html#t:Eq">Eq</a> <a href="SafePrelude.html#t:Bool">Bool</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:Eq:Eq:1" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:-61--61-">(==)</a> :: <a href="SafePrelude.html#t:Bool">Bool</a> -> <a href="SafePrelude.html#t:Bool">Bool</a> -> <a href="SafePrelude.html#t:Bool">Bool</a> <a href="#v:-61--61-" class="selflink">#</a></p><p class="src"><a href="#v:-47--61-">(/=)</a> :: <a href="SafePrelude.html#t:Bool">Bool</a> -> <a href="SafePrelude.html#t:Bool">Bool</a> -> <a href="SafePrelude.html#t:Bool">Bool</a> <a href="#v:-47--61-" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Eq:Eq:2" class="instance expander" onclick="toggleSection('i:ic:Eq:Eq:2')"></span> <a href="SafePrelude.html#t:Eq">Eq</a> <a href="SafePrelude.html#t:Char">Char</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:Eq:Eq:2" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:-61--61-">(==)</a> :: <a href="SafePrelude.html#t:Char">Char</a> -> <a href="SafePrelude.html#t:Char">Char</a> -> <a href="SafePrelude.html#t:Bool">Bool</a> <a href="#v:-61--61-" class="selflink">#</a></p><p class="src"><a href="#v:-47--61-">(/=)</a> :: <a href="SafePrelude.html#t:Char">Char</a> -> <a href="SafePrelude.html#t:Char">Char</a> -> <a href="SafePrelude.html#t:Bool">Bool</a> <a href="#v:-47--61-" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Eq:Eq:3" class="instance expander" onclick="toggleSection('i:ic:Eq:Eq:3')"></span> <a href="SafePrelude.html#t:Eq">Eq</a> <a href="SafePrelude.html#t:Double">Double</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:Eq:Eq:3" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:-61--61-">(==)</a> :: <a href="SafePrelude.html#t:Double">Double</a> -> <a href="SafePrelude.html#t:Double">Double</a> -> <a href="SafePrelude.html#t:Bool">Bool</a> <a href="#v:-61--61-" class="selflink">#</a></p><p class="src"><a href="#v:-47--61-">(/=)</a> :: <a href="SafePrelude.html#t:Double">Double</a> -> <a href="SafePrelude.html#t:Double">Double</a> -> <a href="SafePrelude.html#t:Bool">Bool</a> <a href="#v:-47--61-" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Eq:Eq:4" class="instance expander" onclick="toggleSection('i:ic:Eq:Eq:4')"></span> <a href="SafePrelude.html#t:Eq">Eq</a> <a href="SafePrelude.html#t:Float">Float</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:Eq:Eq:4" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:-61--61-">(==)</a> :: <a href="SafePrelude.html#t:Float">Float</a> -> <a href="SafePrelude.html#t:Float">Float</a> -> <a href="SafePrelude.html#t:Bool">Bool</a> <a href="#v:-61--61-" class="selflink">#</a></p><p class="src"><a href="#v:-47--61-">(/=)</a> ::
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type. <code><a href="SafePrelude.html#t:Ord">Ord</a></code> is not a superclass of <code><a href="SafePrelude.html#t:Bounded">Bounded</a></code> since types that are not
|
||
|
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totally ordered may also have upper and lower bounds.</p><p>The <code><a href="SafePrelude.html#t:Bounded">Bounded</a></code> class may be derived for any enumeration type;
|
||
|
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<code><a href="SafePrelude.html#v:minBound">minBound</a></code> is the first constructor listed in the <code>data</code> declaration
|
||
|
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and <code><a href="SafePrelude.html#v:maxBound">maxBound</a></code> is the last.
|
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<code><a href="SafePrelude.html#t:Bounded">Bounded</a></code> may also be derived for single-constructor datatypes whose
|
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constituent types are in <code><a href="SafePrelude.html#t:Bounded">Bounded</a></code>.</p></div><div class="subs instances"><p id="control.i:Bounded" class="caption collapser" onclick="toggleSection('i:Bounded')">Instances</p><div id="section.i:Bounded" class="show"><table><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Bounded:Bounded:1" class="instance expander" onclick="toggleSection('i:ic:Bounded:Bounded:1')"></span> <a href="SafePrelude.html#t:Bounded">Bounded</a> <a href="SafePrelude.html#t:Bool">Bool</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:Bounded:Bounded:1" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:minBound">minBound</a> :: <a href="SafePrelude.html#t:Bool">Bool</a> <a href="#v:minBound" class="selflink">#</a></p><p class="src"><a href="#v:maxBound">maxBound</a> :: <a href="SafePrelude.html#t:Bool">Bool</a> <a href="#v:maxBound" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Bounded:Bounded:2" class="instance expander" onclick="toggleSection('i:ic:Bounded:Bounded:2')"></span> <a href="SafePrelude.html#t:Bounded">Bounded</a> <a href="SafePrelude.html#t:Char">Char</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:Bounded:Bounded:2" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:minBound">minBound</a> :: <a href="SafePrelude.html#t:Char">Char</a> <a href="#v:minBound" class="selflink">#</a></p><p class="src"><a href="#v:maxBound">maxBound</a> :: <a href="SafePrelude.html#t:Char">Char</a> <a href="#v:maxBound" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Bounded:Bounded:3" class="instance expander" onclick="toggleSection('i:ic:Bounded:Bounded:3')"></span> <a href="SafePrelude.html#t:Bounded">Bounded</a> <a href="SafePrelude.html#t:Int">Int</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:Bounded:Bounded:3" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:minBound">minBound</a> :: <a href="SafePrelude.html#t:Int">Int</a> <a href="#v:minBound" class="selflink">#</a></p><p class="src"><a href="#v:maxBound">maxBound</a> :: <a href="SafePrelude.html#t:Int">Int</a> <a href="#v:maxBound" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Bounded:Bounded:4" class="instance expander" onclick="toggleSection('i:ic:Bounded:Bounded:4')"></span> <a href="SafePrelude.html#t:Bounded">Bounded</a> <a href="SafePrelude.html#t:Int8">Int8</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:Bounded:Bounded:4" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:minBound">minBound</a> :: <a href="SafePrelude.html#t:Int8">Int8</a> <a href="#v:minBound" class="selflink">#</a></p><p class="src"><a href="#v:maxBound">maxBound</a> :: <a href="SafePrelude.html#t:Int8">Int8</a> <a href="#v:maxBound" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Bounded:Bounded:5" class="instance expander" onclick="toggleSection('i:ic:Bounded:Bounded:5')"></span> <a href="SafePrelude.html#t:Bounded">Bounded</a> <a href="SafePrelude.html#t:Int16">Int16</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:Bounded:Bounded:5" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:minBound">minBound</a> :: <a href="SafePrelude.html#t:Int16">Int16</a> <a href="#v:minBound" class="selflink">#</a></p><p class="src"><a href="#v:maxBound">maxBound</a> :: <a href="SafePrelude.html#t:Int16">Int16</a> <a href="#v:maxBound" cl
|
||
|
|
are compatible with derived instances of <code><a href="../base-4.9.0.0/Text-Read.html#v:Read">Read</a></code>:</p><ul><li>The result of <code><a href="SafePrelude.html#v:show">show</a></code> is a syntactically correct Haskell
|
||
|
|
expression containing only constants, given the fixity
|
||
|
|
declarations in force at the point where the type is declared.
|
||
|
|
It contains only the constructor names defined in the data type,
|
||
|
|
parentheses, and spaces. When labelled constructor fields are
|
||
|
|
used, braces, commas, field names, and equal signs are also used.</li><li>If the constructor is defined to be an infix operator, then
|
||
|
|
<code><a href="SafePrelude.html#v:showsPrec">showsPrec</a></code> will produce infix applications of the constructor.</li><li>the representation will be enclosed in parentheses if the
|
||
|
|
precedence of the top-level constructor in <code>x</code> is less than <code>d</code>
|
||
|
|
(associativity is ignored). Thus, if <code>d</code> is <code>0</code> then the result
|
||
|
|
is never surrounded in parentheses; if <code>d</code> is <code>11</code> it is always
|
||
|
|
surrounded in parentheses, unless it is an atomic expression.</li><li>If the constructor is defined using record syntax, then <code><a href="SafePrelude.html#v:show">show</a></code>
|
||
|
|
will produce the record-syntax form, with the fields given in the
|
||
|
|
same order as the original declaration.</li></ul><p>For example, given the declarations</p><pre>infixr 5 :^:
|
||
|
|
data Tree a = Leaf a | Tree a :^: Tree a</pre><p>the derived instance of <code><a href="SafePrelude.html#t:Show">Show</a></code> is equivalent to</p><pre>instance (Show a) => Show (Tree a) where
|
||
|
|
|
||
|
|
showsPrec d (Leaf m) = showParen (d > app_prec) $
|
||
|
|
showString "Leaf " . showsPrec (app_prec+1) m
|
||
|
|
where app_prec = 10
|
||
|
|
|
||
|
|
showsPrec d (u :^: v) = showParen (d > up_prec) $
|
||
|
|
showsPrec (up_prec+1) u .
|
||
|
|
showString " :^: " .
|
||
|
|
showsPrec (up_prec+1) v
|
||
|
|
where up_prec = 5</pre><p>Note that right-associativity of <code>:^:</code> is ignored. For example,</p><ul><li><code><code><a href="SafePrelude.html#v:show">show</a></code> (Leaf 1 :^: Leaf 2 :^: Leaf 3)</code> produces the string
|
||
|
|
<code>"Leaf 1 :^: (Leaf 2 :^: Leaf 3)"</code>.</li></ul></div><div class="subs minimal"><p class="caption">Minimal complete definition</p><p class="src"><a href="SafePrelude.html#v:showsPrec">showsPrec</a> | <a href="SafePrelude.html#v:show">show</a></p></div><div class="subs instances"><p id="control.i:Show" class="caption collapser" onclick="toggleSection('i:Show')">Instances</p><div id="section.i:Show" class="show"><table><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Show:Show:1" class="instance expander" onclick="toggleSection('i:ic:Show:Show:1')"></span> <a href="SafePrelude.html#t:Show">Show</a> <a href="SafePrelude.html#t:Bool">Bool</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:Show:Show:1" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:showsPrec">showsPrec</a> :: <a href="SafePrelude.html#t:Int">Int</a> -> <a href="SafePrelude.html#t:Bool">Bool</a> -> <a href="../base-4.9.0.0/Text-Show.html#t:ShowS">ShowS</a> <a href="#v:showsPrec" class="selflink">#</a></p><p class="src"><a href="#v:show">show</a> :: <a href="SafePrelude.html#t:Bool">Bool</a> -> <a href="SafePrelude.html#t:String">String</a> <a href="#v:show" class="selflink">#</a></p><p class="src"><a href="#v:showList">showList</a> :: [<a href="SafePrelude.html#t:Bool">Bool</a>] -> <a href="../base-4.9.0.0/Text-Show.html#t:ShowS">ShowS</a> <a href="#v:showList" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Show:Show:2" class="instance expander" onclick="toggleSection('i:ic:Show:Show:2')"></span> <a href="SafePrelude.html#t:Show">Show</a> <a href="SafePrelude.html#t:Char">Char</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:Show:Show:2" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:showsPrec">showsPrec</a> :: <a href="SafePrelude.html#t:Int">Int</a> -> <a href="SafePrelude.html#t:Char">Char</a> -> <a href="../base-4.9.0.0/Text-Show.html#t:ShowS">ShowS</a> <a href="#v:showsPrec" class="selflink">#</a></p><p class="src"><a href="#v:show">show</a> :: <a href="SafePrelude.html#t:Char">Char</a> -> <a href="SafePrelude.html#t:String">String</a> <a href="#v:show" class="selflink">#</a></p><p class="src"><a href="#v:showList">showList</a> :: [<a href="SafePrelude.html#t:Char">Char</a>] -> <a href="../base-4.9.0.0/Text-Show.html#t:ShowS">ShowS</a> <a href="#v:showList" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Show:Show:3" class="instance expander" onclick="toggleSection('i:ic:Show:Show:3')"></span> <a href="SafePrelude.html#t:Show">Show</a> <a href="SafePrelude.html#t:Int">Int</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:Show:Show:3" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:showsPrec">showsPrec</a> :: <a href="SafePrelude.html#t:Int">Int</a> -> <a href="SafePrelude.html#t:Int">Int</a> -> <a href="../base-4.9.0.0/Text-Show.html#t:ShowS">ShowS</a> <a href="#v:showsPrec" class="selflink">#</a></p><p class="src"><a href="#v:show">show</a> :: <a href="SafePrelude.html#t:Int">Int</a> -> <a href="SafePrelude.html#t:String">String</a> <a href="#v:show" class="selflink">#</a></p><p class="src"><a href="#v:showList">showList</a> :: [<a href="SafePrelude.html#t:Int">Int</a>] -> <a href="../base-4.9.0.0/Text-Show.html#t:ShowS">ShowS</a> <a href="#v:showList" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Show:Show:4" class="instance expander" onclick="toggleSection('i:ic:Show:Show:4')"></span> <a href="SafePrelude.html#t:Show">Show</a> <a href="SafePrelude.html#t:Int8">Int8</a></span></td><td class="doc empty"> </td></tr><tr><td col
|
||
|
|
<code><a href="SafePrelude.html#t:Identity">Identity</a></code> newtype if the <code><a href="SafePrelude.html#v:runIdentity">runIdentity</a></code> field were removed</p></td></tr><tr><td colspan="2"><div id="section.i:ic:Show:Show:124" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:showsPrec">showsPrec</a> :: <a href="SafePrelude.html#t:Int">Int</a> -> <a href="SafePrelude.html#t:Identity">Identity</a> a -> <a href="../base-4.9.0.0/Text-Show.html#t:ShowS">ShowS</a> <a href="#v:showsPrec" class="selflink">#</a></p><p class="src"><a href="#v:show">show</a> :: <a href="SafePrelude.html#t:Identity">Identity</a> a -> <a href="SafePrelude.html#t:String">String</a> <a href="#v:show" class="selflink">#</a></p><p class="src"><a href="#v:showList">showList</a> :: [<a href="SafePrelude.html#t:Identity">Identity</a> a] -> <a href="../base-4.9.0.0/Text-Show.html#t:ShowS">ShowS</a> <a href="#v:showList" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Show:Show:125" class="instance expander" onclick="toggleSection('i:ic:Show:Show:125')"></span> <a href="SafePrelude.html#t:Show">Show</a> a => <a href="SafePrelude.html#t:Show">Show</a> (<a href="../base-4.9.0.0/Data-Semigroup.html#t:Min">Min</a> a)</span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:Show:Show:125" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:showsPrec">showsPrec</a> :: <a href="SafePrelude.html#t:Int">Int</a> -> <a href="../base-4.9.0.0/Data-Semigroup.html#t:Min">Min</a> a -> <a href="../base-4.9.0.0/Text-Show.html#t:ShowS">ShowS</a> <a href="#v:showsPrec" class="selflink">#</a></p><p class="src"><a href="#v:show">show</a> :: <a href="../base-4.9.0.0/Data-Semigroup.html#t:Min">Min</a> a -> <a href="SafePrelude.html#t:String">String</a> <a href="#v:show" class="selflink">#</a></p><p class="src"><a href="#v:showList">showList</a> :: [<a href="../base-4.9.0.0/Data-Semigroup.html#t:Min">Min</a> a] -> <a href="../base-4.9.0.0/Text-Show.html#t:ShowS">ShowS</a> <a href="#v:showList" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Show:Show:126" class="instance expander" onclick="toggleSection('i:ic:Show:Show:126')"></span> <a href="SafePrelude.html#t:Show">Show</a> a => <a href="SafePrelude.html#t:Show">Show</a> (<a href="../base-4.9.0.0/Data-Semigroup.html#t:Max">Max</a> a)</span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:Show:Show:126" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:showsPrec">showsPrec</a> :: <a href="SafePrelude.html#t:Int">Int</a> -> <a href="../base-4.9.0.0/Data-Semigroup.html#t:Max">Max</a> a -> <a href="../base-4.9.0.0/Text-Show.html#t:ShowS">ShowS</a> <a href="#v:showsPrec" class="selflink">#</a></p><p class="src"><a href="#v:show">show</a> :: <a href="../base-4.9.0.0/Data-Semigroup.html#t:Max">Max</a> a -> <a href="SafePrelude.html#t:String">String</a> <a href="#v:show" class="selflink">#</a></p><p class="src"><a href="#v:showList">showList</a> :: [<a href="../base-4.9.0.0/Data-Semigroup.html#t:Max">Max</a> a] -> <a href="../base-4.9.0.0/Text-Show.html#t:ShowS">ShowS</a> <a href="#v:showList" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Show:Show:127" class="instance expander" onclick="toggleSection('i:ic:Show:Show:127')"></span> <a href="SafePrelude.html#t:Show">Show</a> a => <a href="SafePrelude.html#t:Show">Show</a> (<a href="../base-4.9.0.0/Data-Semigroup.html#t:First">First</a> a)</span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:Show:Show:127" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:showsPrec">showsP
|
||
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<code><a href="../base-4.9.0.0/Data-Functor-Const.html#t:Const">Const</a></code> newtype if the <code>runConst</code> field were removed</p></td></tr><tr><td colspan="2"><div id="section.i:ic:Show:Show:164" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:showsPrec">showsPrec</a> :: <a href="SafePrelude.html#t:Int">Int</a> -> <a href="../base-4.9.0.0/Data-Functor-Const.html#t:Const">Const</a> k a b -> <a href="../base-4.9.0.0/Text-Show.html#t:ShowS">ShowS</a> <a href="#v:showsPrec" class="selflink">#</a></p><p class="src"><a href="#v:show">show</a> :: <a href="../base-4.9.0.0/Data-Functor-Const.html#t:Const">Const</a> k a b -> <a href="SafePrelude.html#t:String">String</a> <a href="#v:show" class="selflink">#</a></p><p class="src"><a href="#v:showList">showList</a> :: [<a href="../base-4.9.0.0/Data-Functor-Const.html#t:Const">Const</a> k a b] -> <a href="../base-4.9.0.0/Text-Show.html#t:ShowS">ShowS</a> <a href="#v:showList" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Show:Show:165" class="instance expander" onclick="toggleSection('i:ic:Show:Show:165')"></span> <a href="SafePrelude.html#t:Show">Show</a> (f a) => <a href="SafePrelude.html#t:Show">Show</a> (<a href="../base-4.9.0.0/Data-Monoid.html#t:Alt">Alt</a> k f a)</span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:Show:Show:165" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:showsPrec">showsPrec</a> :: <a href="SafePrelude.html#t:Int">Int</a> -> <a href="../base-4.9.0.0/Data-Monoid.html#t:Alt">Alt</a> k f a -> <a href="../base-4.9.0.0/Text-Show.html#t:ShowS">ShowS</a> <a href="#v:showsPrec" class="selflink">#</a></p><p class="src"><a href="#v:show">show</a> :: <a href="../base-4.9.0.0/Data-Monoid.html#t:Alt">Alt</a> k f a -> <a href="SafePrelude.html#t:String">String</a> <a href="#v:show" class="selflink">#</a></p><p class="src"><a href="#v:showList">showList</a> :: [<a href="../base-4.9.0.0/Data-Monoid.html#t:Alt">Alt</a> k f a] -> <a href="../base-4.9.0.0/Text-Show.html#t:ShowS">ShowS</a> <a href="#v:showList" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Show:Show:166" class="instance expander" onclick="toggleSection('i:ic:Show:Show:166')"></span> <a href="SafePrelude.html#t:Show">Show</a> (<a href="../base-4.9.0.0/Data-Type-Equality.html#t::-126-:">(:~:)</a> k a b)</span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:Show:Show:166" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:showsPrec">showsPrec</a> :: <a href="SafePrelude.html#t:Int">Int</a> -> (k <a href="../base-4.9.0.0/Data-Type-Equality.html#t::-126-:">:~:</a> a) b -> <a href="../base-4.9.0.0/Text-Show.html#t:ShowS">ShowS</a> <a href="#v:showsPrec" class="selflink">#</a></p><p class="src"><a href="#v:show">show</a> :: (k <a href="../base-4.9.0.0/Data-Type-Equality.html#t::-126-:">:~:</a> a) b -> <a href="SafePrelude.html#t:String">String</a> <a href="#v:show" class="selflink">#</a></p><p class="src"><a href="#v:showList">showList</a> :: [(k <a href="../base-4.9.0.0/Data-Type-Equality.html#t::-126-:">:~:</a> a) b] -> <a href="../base-4.9.0.0/Text-Show.html#t:ShowS">ShowS</a> <a href="#v:showList" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Show:Show:167" class="instance expander" onclick="toggleSection('i:ic:Show:Show:167')"></span> (<a href="SafePrelude.html#t:Show">Show</a> e, <a href="../base-4.9.0.0/Data-Functor-Classes.html#t:Show1">Show1</a> m, <a href="SafePrelude.html#t:Show">Show</a> a) => <a href="SafePrelude.html#t:Show">Show</a> (<a href="../mtl-2.2.1/Control-Monad-Error.html#t:ErrorT">ErrorT</a> e m a)</span></td><td class="doc empty"> </td></tr><tr><td c
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derived instances of <code><a href="../base-4.9.0.0/Text-Show.html#v:Show">Show</a></code> obey:</p><ul><li>If the constructor is defined to be an infix operator, then the
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derived <code><a href="SafePrelude.html#t:Read">Read</a></code> instance will parse only infix applications of
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the constructor (not the prefix form).</li><li>Associativity is not used to reduce the occurrence of parentheses,
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although precedence may be.</li><li>If the constructor is defined using record syntax, the derived <code><a href="SafePrelude.html#t:Read">Read</a></code>
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will parse only the record-syntax form, and furthermore, the fields
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must be given in the same order as the original declaration.</li><li>The derived <code><a href="SafePrelude.html#t:Read">Read</a></code> instance allows arbitrary Haskell whitespace
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between tokens of the input string. Extra parentheses are also
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allowed.</li></ul><p>For example, given the declarations</p><pre>infixr 5 :^:
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data Tree a = Leaf a | Tree a :^: Tree a</pre><p>the derived instance of <code><a href="SafePrelude.html#t:Read">Read</a></code> in Haskell 2010 is equivalent to</p><pre>instance (Read a) => Read (Tree a) where
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readsPrec d r = readParen (d > app_prec)
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(\r -> [(Leaf m,t) |
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("Leaf",s) <- lex r,
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(m,t) <- readsPrec (app_prec+1) s]) r
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++ readParen (d > up_prec)
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(\r -> [(u:^:v,w) |
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(u,s) <- readsPrec (up_prec+1) r,
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(":^:",t) <- lex s,
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(v,w) <- readsPrec (up_prec+1) t]) r
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where app_prec = 10
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up_prec = 5</pre><p>Note that right-associativity of <code>:^:</code> is unused.</p><p>The derived instance in GHC is equivalent to</p><pre>instance (Read a) => Read (Tree a) where
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readPrec = parens $ (prec app_prec $ do
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Ident "Leaf" <- lexP
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m <- step readPrec
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return (Leaf m))
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+++ (prec up_prec $ do
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u <- step readPrec
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Symbol ":^:" <- lexP
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v <- step readPrec
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return (u :^: v))
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where app_prec = 10
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up_prec = 5
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readListPrec = readListPrecDefault</pre></div><div class="subs minimal"><p class="caption">Minimal complete definition</p><p class="src"><a href="SafePrelude.html#v:readsPrec">readsPrec</a> | <a href="SafePrelude.html#v:readPrec">readPrec</a></p></div><div class="subs instances"><p id="control.i:Read" class="caption collapser" onclick="toggleSection('i:Read')">Instances</p><div id="section.i:Read" class="show"><table><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Read:Read:1" class="instance expander" onclick="toggleSection('i:ic:Read:Read:1')"></span> <a href="SafePrelude.html#t:Read">Read</a> <a href="SafePrelude.html#t:Bool">Bool</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:Read:Read:1" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:readsPrec">readsPrec</a> :: <a href="SafePrelude.html#t:Int">Int</a> -> <a href="../base-4.9.0.0/Text-ParserCombinators-ReadP.html#t:ReadS">ReadS</a> <a href="SafePrelude.html#t:Bool">Bool</a> <a href="#v:readsPrec" class="selflink">#</a></p><p class="src"><a href="#v:readList">readList</a> :: <a href="../base-4.9.0.0/Text-ParserCombinators-ReadP.html#t:ReadS">ReadS</a> [<a href="SafePrelude.html#t:Bool">Bool</a>] <a href="#v:readList" class="selflink">#</a></p><p class="src"><a href="#v:readPrec">readPrec</a> :: <a href="../base-4.9.0.0/Text-ParserCombinators-ReadPrec.html#t:ReadPrec">ReadPrec</a> <a href="SafePrelude.html#t:Bool">Bool</a> <a href="#v:readPrec" class="selflink">#</a></p><p class="src"><a href="#v:readListPrec">readListPrec</a> :: <a href="../base-4.9.0.0/Text-ParserCombinators-ReadPrec.html#t:ReadPrec">ReadPrec</a> [<a href="SafePrelude.html#t:Bool">Bool</a>] <a href="#v:readListPrec" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Read:Read:2" class="instance expander" onclick="toggleSection('i:ic:Read:Read:2')"></span> <a href="SafePrelude.html#t:Read">Read</a> <a href="SafePrelude.html#t:Char">Char</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:Read:Read:2" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:readsPrec">readsPrec</a> :: <a href="SafePrelude.html#t:Int">Int</a> -> <a href="../base-4.9.0.0/Text-ParserCombinators-ReadP.html#t:ReadS">ReadS</a> <a href="SafePrelude.html#t:Char">Char</a> <a href="#v:readsPrec" class="selflink">#</a></p><p class="src"><a href="#v:readList">readList</a> :: <a href="../base-4.9.0.0/Text-ParserCombinators-ReadP.html#t:ReadS">ReadS</a> [<a href="SafePrelude.html#t:Char">Char</a>] <a href="#v:readList" class="selflink">#</a></p><p class="src"><a href="#v:readPrec">readPrec</a> :: <a href="../base-4.9.0.0/Text-ParserCombinators-ReadPrec.html#t:ReadPrec">ReadPrec</a> <a href="SafePrelude.html#t:Char">Char</a> <a href="#v:readPrec" class="selflink">#</a></p><p class="src"><a href="#v:readListPrec">readListPrec</a> :: <a href="../base-4.9.0.0/Text-ParserCombinators-ReadPrec.html#t:ReadPrec">ReadPrec</a> [<a href="SafePrelude.html#t:Char">Char</a>] <a href="#v:readListPrec" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Read:Read:3" class="instance expander" onclick="toggleSection('i:ic:Read:Read:3')"></span> <a href="SafePrelude.html#t:Read">Read</a> <a href="SafePrelude.html#t:Double">Double</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:Read:Read:3" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:readsPrec">readsPrec</a> :: <a href="SafePrelude.html#t:Int">Int</a> -> <a href="../base-4.9.0.0/Text-ParserCombinators-ReadP.html#t:ReadS">ReadS</a> <a href="SafePrelude.html#t:Double">Double</a> <a href="#v:readsPrec" class="selflink">#</a></p><p class="src"><a href="#v:readList">readList</a> :: <a href="../base-4.9.0.0/Tex
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<code><a href="../base-4.9.0.0/Data-Void.html#t:Void">Void</a></code> as a data type with no constructors.</p></td></tr><tr><td colspan="2"><div id="section.i:ic:Read:Read:18" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:readsPrec">readsPrec</a> :: <a href="SafePrelude.html#t:Int">Int</a> -> <a href="../base-4.9.0.0/Text-ParserCombinators-ReadP.html#t:ReadS">ReadS</a> <a href="../base-4.9.0.0/Data-Void.html#t:Void">Void</a> <a href="#v:readsPrec" class="selflink">#</a></p><p class="src"><a href="#v:readList">readList</a> :: <a href="../base-4.9.0.0/Text-ParserCombinators-ReadP.html#t:ReadS">ReadS</a> [<a href="../base-4.9.0.0/Data-Void.html#t:Void">Void</a>] <a href="#v:readList" class="selflink">#</a></p><p class="src"><a href="#v:readPrec">readPrec</a> :: <a href="../base-4.9.0.0/Text-ParserCombinators-ReadPrec.html#t:ReadPrec">ReadPrec</a> <a href="../base-4.9.0.0/Data-Void.html#t:Void">Void</a> <a href="#v:readPrec" class="selflink">#</a></p><p class="src"><a href="#v:readListPrec">readListPrec</a> :: <a href="../base-4.9.0.0/Text-ParserCombinators-ReadPrec.html#t:ReadPrec">ReadPrec</a> [<a href="../base-4.9.0.0/Data-Void.html#t:Void">Void</a>] <a href="#v:readListPrec" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Read:Read:19" class="instance expander" onclick="toggleSection('i:ic:Read:Read:19')"></span> <a href="SafePrelude.html#t:Read">Read</a> <a href="../base-4.9.0.0/Data-Version.html#t:Version">Version</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:Read:Read:19" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:readsPrec">readsPrec</a> :: <a href="SafePrelude.html#t:Int">Int</a> -> <a href="../base-4.9.0.0/Text-ParserCombinators-ReadP.html#t:ReadS">ReadS</a> <a href="../base-4.9.0.0/Data-Version.html#t:Version">Version</a> <a href="#v:readsPrec" class="selflink">#</a></p><p class="src"><a href="#v:readList">readList</a> :: <a href="../base-4.9.0.0/Text-ParserCombinators-ReadP.html#t:ReadS">ReadS</a> [<a href="../base-4.9.0.0/Data-Version.html#t:Version">Version</a>] <a href="#v:readList" class="selflink">#</a></p><p class="src"><a href="#v:readPrec">readPrec</a> :: <a href="../base-4.9.0.0/Text-ParserCombinators-ReadPrec.html#t:ReadPrec">ReadPrec</a> <a href="../base-4.9.0.0/Data-Version.html#t:Version">Version</a> <a href="#v:readPrec" class="selflink">#</a></p><p class="src"><a href="#v:readListPrec">readListPrec</a> :: <a href="../base-4.9.0.0/Text-ParserCombinators-ReadPrec.html#t:ReadPrec">ReadPrec</a> [<a href="../base-4.9.0.0/Data-Version.html#t:Version">Version</a>] <a href="#v:readListPrec" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Read:Read:20" class="instance expander" onclick="toggleSection('i:ic:Read:Read:20')"></span> <a href="SafePrelude.html#t:Read">Read</a> <a href="../base-4.9.0.0/System-Exit.html#t:ExitCode">ExitCode</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:Read:Read:20" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:readsPrec">readsPrec</a> :: <a href="SafePrelude.html#t:Int">Int</a> -> <a href="../base-4.9.0.0/Text-ParserCombinators-ReadP.html#t:ReadS">ReadS</a> <a href="../base-4.9.0.0/System-Exit.html#t:ExitCode">ExitCode</a> <a href="#v:readsPrec" class="selflink">#</a></p><p class="src"><a href="#v:readList">readList</a> :: <a href="../base-4.9.0.0/Text-ParserCombinators-ReadP.html#t:ReadS">ReadS</a> [<a href="../base-4.9.0.0/System-Exit.html#t:ExitCode">ExitCode</a>] <a href="#v:readList" class="selflink">#</a></p><p class="src"><a href="#v:readPrec">readPrec</a> :: <a href="../base-4.9.0.0/Text-ParserCombinators-ReadPrec.html#t:ReadPrec">ReadPrec</a> <a href="../base-4.9.0.0/System-Exit.html#t:ExitCode">ExitCode</a> <a href="#v:readPr
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<code><a href="SafePrelude.html#t:Identity">Identity</a></code> newtype if the <code><a href="SafePrelude.html#v:runIdentity">runIdentity</a></code> field were removed</p></td></tr><tr><td colspan="2"><div id="section.i:ic:Read:Read:44" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:readsPrec">readsPrec</a> :: <a href="SafePrelude.html#t:Int">Int</a> -> <a href="../base-4.9.0.0/Text-ParserCombinators-ReadP.html#t:ReadS">ReadS</a> (<a href="SafePrelude.html#t:Identity">Identity</a> a) <a href="#v:readsPrec" class="selflink">#</a></p><p class="src"><a href="#v:readList">readList</a> :: <a href="../base-4.9.0.0/Text-ParserCombinators-ReadP.html#t:ReadS">ReadS</a> [<a href="SafePrelude.html#t:Identity">Identity</a> a] <a href="#v:readList" class="selflink">#</a></p><p class="src"><a href="#v:readPrec">readPrec</a> :: <a href="../base-4.9.0.0/Text-ParserCombinators-ReadPrec.html#t:ReadPrec">ReadPrec</a> (<a href="SafePrelude.html#t:Identity">Identity</a> a) <a href="#v:readPrec" class="selflink">#</a></p><p class="src"><a href="#v:readListPrec">readListPrec</a> :: <a href="../base-4.9.0.0/Text-ParserCombinators-ReadPrec.html#t:ReadPrec">ReadPrec</a> [<a href="SafePrelude.html#t:Identity">Identity</a> a] <a href="#v:readListPrec" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Read:Read:45" class="instance expander" onclick="toggleSection('i:ic:Read:Read:45')"></span> <a href="SafePrelude.html#t:Read">Read</a> a => <a href="SafePrelude.html#t:Read">Read</a> (<a href="../base-4.9.0.0/Data-Semigroup.html#t:Min">Min</a> a)</span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:Read:Read:45" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:readsPrec">readsPrec</a> :: <a href="SafePrelude.html#t:Int">Int</a> -> <a href="../base-4.9.0.0/Text-ParserCombinators-ReadP.html#t:ReadS">ReadS</a> (<a href="../base-4.9.0.0/Data-Semigroup.html#t:Min">Min</a> a) <a href="#v:readsPrec" class="selflink">#</a></p><p class="src"><a href="#v:readList">readList</a> :: <a href="../base-4.9.0.0/Text-ParserCombinators-ReadP.html#t:ReadS">ReadS</a> [<a href="../base-4.9.0.0/Data-Semigroup.html#t:Min">Min</a> a] <a href="#v:readList" class="selflink">#</a></p><p class="src"><a href="#v:readPrec">readPrec</a> :: <a href="../base-4.9.0.0/Text-ParserCombinators-ReadPrec.html#t:ReadPrec">ReadPrec</a> (<a href="../base-4.9.0.0/Data-Semigroup.html#t:Min">Min</a> a) <a href="#v:readPrec" class="selflink">#</a></p><p class="src"><a href="#v:readListPrec">readListPrec</a> :: <a href="../base-4.9.0.0/Text-ParserCombinators-ReadPrec.html#t:ReadPrec">ReadPrec</a> [<a href="../base-4.9.0.0/Data-Semigroup.html#t:Min">Min</a> a] <a href="#v:readListPrec" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Read:Read:46" class="instance expander" onclick="toggleSection('i:ic:Read:Read:46')"></span> <a href="SafePrelude.html#t:Read">Read</a> a => <a href="SafePrelude.html#t:Read">Read</a> (<a href="../base-4.9.0.0/Data-Semigroup.html#t:Max">Max</a> a)</span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:Read:Read:46" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:readsPrec">readsPrec</a> :: <a href="SafePrelude.html#t:Int">Int</a> -> <a href="../base-4.9.0.0/Text-ParserCombinators-ReadP.html#t:ReadS">ReadS</a> (<a href="../base-4.9.0.0/Data-Semigroup.html#t:Max">Max</a> a) <a href="#v:readsPrec" class="selflink">#</a></p><p class="src"><a href="#v:readList">readList</a> :: <a href="../base-4.9.0.0/Text-ParserCombinators-ReadP.html#t:ReadS">ReadS</a> [<a href="../base-4.9.0.0/Data-Semigroup.html#t:Max">Max</a> a] <a href="#v:readList" class="selflink">#</a></p><p class="src"><a href="#v:readPrec">readPrec</a> :: <a href="../base-4.9.0.0/Text-ParserCombinator
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<code><a href="../base-4.9.0.0/Data-Functor-Const.html#t:Const">Const</a></code> newtype if the <code>runConst</code> field were removed</p></td></tr><tr><td colspan="2"><div id="section.i:ic:Read:Read:79" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:readsPrec">readsPrec</a> :: <a href="SafePrelude.html#t:Int">Int</a> -> <a href="../base-4.9.0.0/Text-ParserCombinators-ReadP.html#t:ReadS">ReadS</a> (<a href="../base-4.9.0.0/Data-Functor-Const.html#t:Const">Const</a> k a b) <a href="#v:readsPrec" class="selflink">#</a></p><p class="src"><a href="#v:readList">readList</a> :: <a href="../base-4.9.0.0/Text-ParserCombinators-ReadP.html#t:ReadS">ReadS</a> [<a href="../base-4.9.0.0/Data-Functor-Const.html#t:Const">Const</a> k a b] <a href="#v:readList" class="selflink">#</a></p><p class="src"><a href="#v:readPrec">readPrec</a> :: <a href="../base-4.9.0.0/Text-ParserCombinators-ReadPrec.html#t:ReadPrec">ReadPrec</a> (<a href="../base-4.9.0.0/Data-Functor-Const.html#t:Const">Const</a> k a b) <a href="#v:readPrec" class="selflink">#</a></p><p class="src"><a href="#v:readListPrec">readListPrec</a> :: <a href="../base-4.9.0.0/Text-ParserCombinators-ReadPrec.html#t:ReadPrec">ReadPrec</a> [<a href="../base-4.9.0.0/Data-Functor-Const.html#t:Const">Const</a> k a b] <a href="#v:readListPrec" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Read:Read:80" class="instance expander" onclick="toggleSection('i:ic:Read:Read:80')"></span> <a href="SafePrelude.html#t:Read">Read</a> (f a) => <a href="SafePrelude.html#t:Read">Read</a> (<a href="../base-4.9.0.0/Data-Monoid.html#t:Alt">Alt</a> k f a)</span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:Read:Read:80" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:readsPrec">readsPrec</a> :: <a href="SafePrelude.html#t:Int">Int</a> -> <a href="../base-4.9.0.0/Text-ParserCombinators-ReadP.html#t:ReadS">ReadS</a> (<a href="../base-4.9.0.0/Data-Monoid.html#t:Alt">Alt</a> k f a) <a href="#v:readsPrec" class="selflink">#</a></p><p class="src"><a href="#v:readList">readList</a> :: <a href="../base-4.9.0.0/Text-ParserCombinators-ReadP.html#t:ReadS">ReadS</a> [<a href="../base-4.9.0.0/Data-Monoid.html#t:Alt">Alt</a> k f a] <a href="#v:readList" class="selflink">#</a></p><p class="src"><a href="#v:readPrec">readPrec</a> :: <a href="../base-4.9.0.0/Text-ParserCombinators-ReadPrec.html#t:ReadPrec">ReadPrec</a> (<a href="../base-4.9.0.0/Data-Monoid.html#t:Alt">Alt</a> k f a) <a href="#v:readPrec" class="selflink">#</a></p><p class="src"><a href="#v:readListPrec">readListPrec</a> :: <a href="../base-4.9.0.0/Text-ParserCombinators-ReadPrec.html#t:ReadPrec">ReadPrec</a> [<a href="../base-4.9.0.0/Data-Monoid.html#t:Alt">Alt</a> k f a] <a href="#v:readListPrec" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Read:Read:81" class="instance expander" onclick="toggleSection('i:ic:Read:Read:81')"></span> (~) k a b => <a href="SafePrelude.html#t:Read">Read</a> (<a href="../base-4.9.0.0/Data-Type-Equality.html#t::-126-:">(:~:)</a> k a b)</span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:Read:Read:81" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:readsPrec">readsPrec</a> :: <a href="SafePrelude.html#t:Int">Int</a> -> <a href="../base-4.9.0.0/Text-ParserCombinators-ReadP.html#t:ReadS">ReadS</a> ((k <a href="../base-4.9.0.0/Data-Type-Equality.html#t::-126-:">:~:</a> a) b) <a href="#v:readsPrec" class="selflink">#</a></p><p class="src"><a href="#v:readList">readList</a> :: <a href="../base-4.9.0.0/Text-ParserCombinators-ReadP.html#t:ReadS">ReadS</a> [(k <a href="../base-4.9.0.0/Data-Type-Equality.html#t::-126-:">:~:</a> a) b] <a href="#v:readList" class="selflink">#</a></p><p class="src"><a href="#v:rea
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Instances of <code><a href="SafePrelude.html#t:Functor">Functor</a></code> should satisfy the following laws:</p><pre>fmap id == id
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fmap (f . g) == fmap f . fmap g</pre><p>The instances of <code><a href="SafePrelude.html#t:Functor">Functor</a></code> for lists, <code><a href="../base-4.9.0.0/Data-Maybe.html#v:Maybe">Maybe</a></code> and <code><a href="../base-4.9.0.0/System-IO.html#v:IO">IO</a></code>
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satisfy these laws.</p></div><div class="subs minimal"><p class="caption">Minimal complete definition</p><p class="src"><a href="SafePrelude.html#v:fmap">fmap</a></p></div><div class="subs instances"><p id="control.i:Functor" class="caption collapser" onclick="toggleSection('i:Functor')">Instances</p><div id="section.i:Functor" class="show"><table><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Functor:Functor:1" class="instance expander" onclick="toggleSection('i:ic:Functor:Functor:1')"></span> <a href="SafePrelude.html#t:Functor">Functor</a> []</span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:Functor:Functor:1" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:fmap">fmap</a> :: (a -> b) -> [a] -> [b] <a href="#v:fmap" class="selflink">#</a></p><p class="src"><a href="#v:-60--36-">(<$)</a> :: a -> [b] -> [a] <a href="#v:-60--36-" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Functor:Functor:2" class="instance expander" onclick="toggleSection('i:ic:Functor:Functor:2')"></span> <a href="SafePrelude.html#t:Functor">Functor</a> <a href="SafePrelude.html#t:Maybe">Maybe</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:Functor:Functor:2" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:fmap">fmap</a> :: (a -> b) -> <a href="SafePrelude.html#t:Maybe">Maybe</a> a -> <a href="SafePrelude.html#t:Maybe">Maybe</a> b <a href="#v:fmap" class="selflink">#</a></p><p class="src"><a href="#v:-60--36-">(<$)</a> :: a -> <a href="SafePrelude.html#t:Maybe">Maybe</a> b -> <a href="SafePrelude.html#t:Maybe">Maybe</a> a <a href="#v:-60--36-" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Functor:Functor:3" class="instance expander" onclick="toggleSection('i:ic:Functor:Functor:3')"></span> <a href="SafePrelude.html#t:Functor">Functor</a> <a href="SafePrelude.html#t:IO">IO</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:Functor:Functor:3" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:fmap">fmap</a> :: (a -> b) -> <a href="SafePrelude.html#t:IO">IO</a> a -> <a href="SafePrelude.html#t:IO">IO</a> b <a href="#v:fmap" class="selflink">#</a></p><p class="src"><a href="#v:-60--36-">(<$)</a> :: a -> <a href="SafePrelude.html#t:IO">IO</a> b -> <a href="SafePrelude.html#t:IO">IO</a> a <a href="#v:-60--36-" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Functor:Functor:4" class="instance expander" onclick="toggleSection('i:ic:Functor:Functor:4')"></span> <a href="SafePrelude.html#t:Functor">Functor</a> <a href="../base-4.9.0.0/GHC-Generics.html#t:V1">V1</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:Functor:Functor:4" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:fmap">fmap</a> :: (a -> b) -> <a href="../base-4.9.0.0/GHC-Generics.html#t:V1">V1</a> a -> <a href="../base-4.9.0.0/GHC-Generics.html#t:V1">V1</a> b <a href="#v:fmap" class="selflink">#</a></p><p class="src"><a href="#v:-60--36-">(<$)</a> :: a -> <a href="../base-4.9.0.0/GHC-Generics.html#t:V1">V1</a> b -> <a href="../base-4.9.0.0/GHC-Generics.html#t:V1">V1</a> a <a href="#v:-60--36-" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Functor:Functor:5" class="instance expander" onclick="toggleSection('i:ic:Functor:Functor:5')"></span> <a href="SafePrelude.html#t:Functor">Functor</a> <a href="../base-4.9.0.0/GHC-Generics.html#t:U1">U1</a></span></td><td class="doc empty"> </t
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functions satisfying the following laws:</p><dl><dt><em>identity</em></dt><dd><pre><code><a href="SafePrelude.html#v:pure">pure</a></code> <code><a href="SafePrelude.html#v:id">id</a></code> <code><a href="SafePrelude.html#v:-60--42--62-"><*></a></code> v = v</pre></dd><dt><em>composition</em></dt><dd><pre><code><a href="SafePrelude.html#v:pure">pure</a></code> (.) <code><a href="SafePrelude.html#v:-60--42--62-"><*></a></code> u <code><a href="SafePrelude.html#v:-60--42--62-"><*></a></code> v <code><a href="SafePrelude.html#v:-60--42--62-"><*></a></code> w = u <code><a href="SafePrelude.html#v:-60--42--62-"><*></a></code> (v <code><a href="SafePrelude.html#v:-60--42--62-"><*></a></code> w)</pre></dd><dt><em>homomorphism</em></dt><dd><pre><code><a href="SafePrelude.html#v:pure">pure</a></code> f <code><a href="SafePrelude.html#v:-60--42--62-"><*></a></code> <code><a href="SafePrelude.html#v:pure">pure</a></code> x = <code><a href="SafePrelude.html#v:pure">pure</a></code> (f x)</pre></dd><dt><em>interchange</em></dt><dd><pre>u <code><a href="SafePrelude.html#v:-60--42--62-"><*></a></code> <code><a href="SafePrelude.html#v:pure">pure</a></code> y = <code><a href="SafePrelude.html#v:pure">pure</a></code> (<code><a href="SafePrelude.html#v:-36-">$</a></code> y) <code><a href="SafePrelude.html#v:-60--42--62-"><*></a></code> u</pre></dd></dl><p>The other methods have the following default definitions, which may
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be overridden with equivalent specialized implementations:</p><ul><li><pre>u <code><a href="SafePrelude.html#v:-42--62-">*></a></code> v = <code><a href="SafePrelude.html#v:pure">pure</a></code> (<code><a href="SafePrelude.html#v:const">const</a></code> <code><a href="SafePrelude.html#v:id">id</a></code>) <code><a href="SafePrelude.html#v:-60--42--62-"><*></a></code> u <code><a href="SafePrelude.html#v:-60--42--62-"><*></a></code> v</pre></li><li><pre>u <code><a href="SafePrelude.html#v:-60--42-"><*</a></code> v = <code><a href="SafePrelude.html#v:pure">pure</a></code> <code><a href="SafePrelude.html#v:const">const</a></code> <code><a href="SafePrelude.html#v:-60--42--62-"><*></a></code> u <code><a href="SafePrelude.html#v:-60--42--62-"><*></a></code> v</pre></li></ul><p>As a consequence of these laws, the <code><a href="SafePrelude.html#t:Functor">Functor</a></code> instance for <code>f</code> will satisfy</p><ul><li><pre><code><a href="SafePrelude.html#v:fmap">fmap</a></code> f x = <code><a href="SafePrelude.html#v:pure">pure</a></code> f <code><a href="SafePrelude.html#v:-60--42--62-"><*></a></code> x</pre></li></ul><p>If <code>f</code> is also a <code><a href="SafePrelude.html#t:Monad">Monad</a></code>, it should satisfy</p><ul><li><pre><code><a href="SafePrelude.html#v:pure">pure</a></code> = <code><a href="SafePrelude.html#v:return">return</a></code></pre></li><li><pre>(<code><a href="SafePrelude.html#v:-60--42--62-"><*></a></code>) = <code><a href="SafePrelude.html#v:ap">ap</a></code></pre></li></ul><p>(which implies that <code><a href="SafePrelude.html#v:pure">pure</a></code> and <code><a href="SafePrelude.html#v:-60--42--62-"><*></a></code> satisfy the applicative functor laws).</p></div><div class="subs minimal"><p class="caption">Minimal complete definition</p><p class="src"><a href="SafePrelude.html#v:pure">pure</a>, <a href="SafePrelude.html#v:-60--42--62-">(<*>)</a></p></div><div class="subs instances"><p id="control.i:Applicative" class="caption collapser" onclick="toggleSection('i:Applicative')">Instances</p><div id="section.i:Applicative" class="show"><table><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Applicative:Applicative:1" class="instance expander" onclick="toggleSection('i:ic:Applicative:Applicative:1')"></span> <a href="SafePrelude.html#t:Applicative">Applicative</a> []</span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:Applicative:Applicative:1" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:pure">pure</a> :: a -> [a] <a href="#v:pure" class="selflink">#</a></p><p class="src"><a href="#v:-60--42--62-">(<*>)</a> :: [a -> b] -> [a] -> [b] <a href="#v:-60--42--62-" class="selflink">#</a></p><p class="src"><a href="#v:-42--62-">(*>)</a> :: [a] -> [b] -> [b] <a href="#v:-42--62-" class="selflink">#</a></p><p class="src"><a href="#v:-60--42-">(<*)</a> :: [a] -> [b] -> [a] <a href="#v:-60--42-" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Applicative:Applicative:2" class="instance expander" onclick="toggleSection('i:ic:Applicative:Applicative:2')"></span> <a href="SafePrelude.html#t:Applicative">Applicative</a> <a href="SafePrelude.html#t:Maybe">Maybe</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:Applicative:Applicative:2" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:pure">pure</a> :: a -> <a href="SafePrelude.html#t:Maybe">Maybe</a> a <a href="#v:pure" class="selflink">#</a></p><p class="src"><a href="#v:-60--42--62-">(<*>)</a> :: <a href="SafePrelude.html#t:Maybe">Maybe</a> (a -> b) -> <a href="SafePrelude.html#t:Maybe">Maybe</a> a -> <a href="SafePrelude.html#t:Maybe">Maybe</a> b <a href="#v:-60--42--62-" class="selflink">#</a></p><p class="src"><a href="#v:-42--62-">(*>
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of the equations:</p><ul><li><pre>some v = (:) <code><$></code> v <code><a href="SafePrelude.html#v:-60--42--62-"><*></a></code> many v</pre></li><li><pre>many v = some v <code><a href="SafePrelude.html#v:-60--124--62-"><|></a></code> <code><a href="SafePrelude.html#v:pure">pure</a></code> []</pre></li></ul></div><div class="subs minimal"><p class="caption">Minimal complete definition</p><p class="src"><a href="SafePrelude.html#v:empty">empty</a>, <a href="SafePrelude.html#v:-60--124--62-">(<|>)</a></p></div><div class="subs instances"><p id="control.i:Alternative" class="caption collapser" onclick="toggleSection('i:Alternative')">Instances</p><div id="section.i:Alternative" class="show"><table><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Alternative:Alternative:1" class="instance expander" onclick="toggleSection('i:ic:Alternative:Alternative:1')"></span> <a href="SafePrelude.html#t:Alternative">Alternative</a> []</span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:Alternative:Alternative:1" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:empty">empty</a> :: [a] <a href="#v:empty" class="selflink">#</a></p><p class="src"><a href="#v:-60--124--62-">(<|>)</a> :: [a] -> [a] -> [a] <a href="#v:-60--124--62-" class="selflink">#</a></p><p class="src"><a href="#v:some">some</a> :: [a] -> [[a]] <a href="#v:some" class="selflink">#</a></p><p class="src"><a href="#v:many">many</a> :: [a] -> [[a]] <a href="#v:many" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Alternative:Alternative:2" class="instance expander" onclick="toggleSection('i:ic:Alternative:Alternative:2')"></span> <a href="SafePrelude.html#t:Alternative">Alternative</a> <a href="SafePrelude.html#t:Maybe">Maybe</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:Alternative:Alternative:2" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:empty">empty</a> :: <a href="SafePrelude.html#t:Maybe">Maybe</a> a <a href="#v:empty" class="selflink">#</a></p><p class="src"><a href="#v:-60--124--62-">(<|>)</a> :: <a href="SafePrelude.html#t:Maybe">Maybe</a> a -> <a href="SafePrelude.html#t:Maybe">Maybe</a> a -> <a href="SafePrelude.html#t:Maybe">Maybe</a> a <a href="#v:-60--124--62-" class="selflink">#</a></p><p class="src"><a href="#v:some">some</a> :: <a href="SafePrelude.html#t:Maybe">Maybe</a> a -> <a href="SafePrelude.html#t:Maybe">Maybe</a> [a] <a href="#v:some" class="selflink">#</a></p><p class="src"><a href="#v:many">many</a> :: <a href="SafePrelude.html#t:Maybe">Maybe</a> a -> <a href="SafePrelude.html#t:Maybe">Maybe</a> [a] <a href="#v:many" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Alternative:Alternative:3" class="instance expander" onclick="toggleSection('i:ic:Alternative:Alternative:3')"></span> <a href="SafePrelude.html#t:Alternative">Alternative</a> <a href="SafePrelude.html#t:IO">IO</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:Alternative:Alternative:3" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:empty">empty</a> :: <a href="SafePrelude.html#t:IO">IO</a> a <a href="#v:empty" class="selflink">#</a></p><p class="src"><a href="#v:-60--124--62-">(<|>)</a> :: <a href="SafePrelude.html#t:IO">IO</a> a -> <a href="SafePrelude.html#t:IO">IO</a> a -> <a href="SafePrelude.html#t:IO">IO</a> a <a href="#v:-60--124--62-" class="selflink">#</a></p><p class="src"><a href="#v:some">some</a> :: <a href="SafePrelude.html#t:IO">IO</a> a -> <a href="SafePrelude.html#t:IO">IO</a> [a] <a href="#v:some" class="selflink">#</a></p><p class="src"><a href="#v:many">many</a> :: <a href="SafePrelude.html#t:IO">IO</a> a
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a concept from a branch of mathematics known as <em>category theory</em>.
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From the perspective of a Haskell programmer, however, it is best to
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think of a monad as an <em>abstract datatype</em> of actions.
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Haskell's <code>do</code> expressions provide a convenient syntax for writing
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monadic expressions.</p><p>Instances of <code><a href="SafePrelude.html#t:Monad">Monad</a></code> should satisfy the following laws:</p><ul><li><pre><code><a href="SafePrelude.html#v:return">return</a></code> a <code><a href="SafePrelude.html#v:-62--62--61-">>>=</a></code> k = k a</pre></li><li><pre>m <code><a href="SafePrelude.html#v:-62--62--61-">>>=</a></code> <code><a href="SafePrelude.html#v:return">return</a></code> = m</pre></li><li><pre>m <code><a href="SafePrelude.html#v:-62--62--61-">>>=</a></code> (x -> k x <code><a href="SafePrelude.html#v:-62--62--61-">>>=</a></code> h) = (m <code><a href="SafePrelude.html#v:-62--62--61-">>>=</a></code> k) <code><a href="SafePrelude.html#v:-62--62--61-">>>=</a></code> h</pre></li></ul><p>Furthermore, the <code><a href="SafePrelude.html#t:Monad">Monad</a></code> and <code><a href="SafePrelude.html#t:Applicative">Applicative</a></code> operations should relate as follows:</p><ul><li><pre><code><a href="SafePrelude.html#v:pure">pure</a></code> = <code><a href="SafePrelude.html#v:return">return</a></code></pre></li><li><pre>(<code><a href="SafePrelude.html#v:-60--42--62-"><*></a></code>) = <code><a href="SafePrelude.html#v:ap">ap</a></code></pre></li></ul><p>The above laws imply:</p><ul><li><pre><code><a href="SafePrelude.html#v:fmap">fmap</a></code> f xs = xs <code><a href="SafePrelude.html#v:-62--62--61-">>>=</a></code> <code><a href="SafePrelude.html#v:return">return</a></code> . f</pre></li><li><pre>(<code><a href="SafePrelude.html#v:-62--62-">>></a></code>) = (<code><a href="SafePrelude.html#v:-42--62-">*></a></code>)</pre></li></ul><p>and that <code><a href="SafePrelude.html#v:pure">pure</a></code> and (<code><a href="SafePrelude.html#v:-60--42--62-"><*></a></code>) satisfy the applicative functor laws.</p><p>The instances of <code><a href="SafePrelude.html#t:Monad">Monad</a></code> for lists, <code><a href="../base-4.9.0.0/Data-Maybe.html#v:Maybe">Maybe</a></code> and <code><a href="../base-4.9.0.0/System-IO.html#v:IO">IO</a></code>
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defined in the <a href="../base-4.9.0.0/Prelude.html">Prelude</a> satisfy these laws.</p></div><div class="subs minimal"><p class="caption">Minimal complete definition</p><p class="src"><a href="SafePrelude.html#v:-62--62--61-">(>>=)</a></p></div><div class="subs instances"><p id="control.i:Monad" class="caption collapser" onclick="toggleSection('i:Monad')">Instances</p><div id="section.i:Monad" class="show"><table><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Monad:Monad:1" class="instance expander" onclick="toggleSection('i:ic:Monad:Monad:1')"></span> <a href="SafePrelude.html#t:Monad">Monad</a> []</span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:Monad:Monad:1" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:-62--62--61-">(>>=)</a> :: [a] -> (a -> [b]) -> [b] <a href="#v:-62--62--61-" class="selflink">#</a></p><p class="src"><a href="#v:-62--62-">(>>)</a> :: [a] -> [b] -> [b] <a href="#v:-62--62-" class="selflink">#</a></p><p class="src"><a href="#v:return">return</a> :: a -> [a] <a href="#v:return" class="selflink">#</a></p><p class="src"><a href="#v:fail">fail</a> :: <a href="SafePrelude.html#t:String">String</a> -> [a] <a href="#v:fail" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Monad:Monad:2" class="instance expander" onclick="toggleSection('i:ic:Monad:Monad:2')"></span> <a href="SafePrelude.html#t:Monad">Monad</a> <a href="SafePrelude.html#t:Maybe">Maybe</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:Monad:Monad:2" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:-62--62--61-">(>>=)</a> :: <a href="SafePrelude.html#t:Maybe">Maybe</a> a -> (a -> <a href="SafePrelude.html#t:Maybe">Maybe</a> b) -> <a href="SafePrelude.html#t:Maybe">Maybe</a> b <a href="#v:-62--62--61-" class="selflink">#</a></p><p class="src"><a href="#v:-62--62-">(>>)</a> :: <a href="SafePrelude.html#t:Maybe">Maybe</a> a -> <a href="SafePrelude.html#t:Maybe">Maybe</a> b -> <a href="SafePrelude.html#t:Maybe">Maybe</a> b <a href="#v:-62--62-" class="selflink">#</a></p><p class="src"><a href="#v:return">return</a> :: a -> <a href="SafePrelude.html#t:Maybe">Maybe</a> a <a href="#v:return" class="selflink">#</a></p><p class="src"><a href="#v:fail">fail</a> :: <a href="SafePrelude.html#t:String">String</a> -> <a href="SafePrelude.html#t:Maybe">Maybe</a> a <a href="#v:fail" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Monad:Monad:3" class="instance expander" onclick="toggleSection('i:ic:Monad:Monad:3')"></span> <a href="SafePrelude.html#t:Monad">Monad</a> <a href="SafePrelude.html#t:IO">IO</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:Monad:Monad:3" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:-62--62--61-">(>>=)</a> :: <a href="SafePrelude.html#t:IO">IO</a> a -> (a -> <a href="SafePrelude.html#t:IO">IO</a> b) -> <a href="SafePrelude.html#t:IO">IO</a> b <a href="#v:-62--62--61-" class="selflink">#</a></p><p class="src"><a href="#v:-62--62-">(>>)</a> :: <a href="SafePrelude.html#t:IO">IO</a> a -> <a href="SafePrelude.html#t:IO">IO</a> b -> <a href="SafePrelude.html#t:IO">IO</a> b <a href="#v:-62--62-" class="selflink">#</a></p><p class="src"><a href="#v:return">return</a> :: a -> <a href="SafePrelude.html#t:IO">IO</a> a <a href="#v:return" class="selflink">#</a></p><p class="src"><a href="#v:fail">fail</a> :: <a href="SafePrelude.html#t:String">String</a> -> <a href="SafePrelude.html#t:IO">IO</a> a <a href="#v:fail" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Monad:Monad
|
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Any monad built by applying a sequence of monad transformers to the
|
||
|
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<code><a href="SafePrelude.html#t:IO">IO</a></code> monad will be an instance of this class.</p><p>Instances should satisfy the following laws, which state that <code><a href="SafePrelude.html#v:liftIO">liftIO</a></code>
|
||
|
|
is a transformer of monads:</p><ul><li><pre><code><a href="SafePrelude.html#v:liftIO">liftIO</a></code> . <code><a href="SafePrelude.html#v:return">return</a></code> = <code><a href="SafePrelude.html#v:return">return</a></code></pre></li><li><pre><code><a href="SafePrelude.html#v:liftIO">liftIO</a></code> (m >>= f) = <code><a href="SafePrelude.html#v:liftIO">liftIO</a></code> m >>= (<code><a href="SafePrelude.html#v:liftIO">liftIO</a></code> . f)</pre></li></ul></div><div class="subs instances"><p id="control.i:MonadIO" class="caption collapser" onclick="toggleSection('i:MonadIO')">Instances</p><div id="section.i:MonadIO" class="show"><table><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:MonadIO:MonadIO:1" class="instance expander" onclick="toggleSection('i:ic:MonadIO:MonadIO:1')"></span> <a href="SafePrelude.html#t:MonadIO">MonadIO</a> <a href="SafePrelude.html#t:IO">IO</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:MonadIO:MonadIO:1" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:liftIO">liftIO</a> :: <a href="SafePrelude.html#t:IO">IO</a> a -> <a href="SafePrelude.html#t:IO">IO</a> a <a href="#v:liftIO" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:MonadIO:MonadIO:2" class="instance expander" onclick="toggleSection('i:ic:MonadIO:MonadIO:2')"></span> (<a href="../mtl-2.2.1/Control-Monad-Error-Class.html#t:Error">Error</a> e, <a href="SafePrelude.html#t:MonadIO">MonadIO</a> m) => <a href="SafePrelude.html#t:MonadIO">MonadIO</a> (<a href="../mtl-2.2.1/Control-Monad-Error.html#t:ErrorT">ErrorT</a> e m)</span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:MonadIO:MonadIO:2" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:liftIO">liftIO</a> :: <a href="SafePrelude.html#t:IO">IO</a> a -> <a href="../mtl-2.2.1/Control-Monad-Error.html#t:ErrorT">ErrorT</a> e m a <a href="#v:liftIO" class="selflink">#</a></p></div></div></td></tr></table></div></div></div><div class="top"><p class="src"><span class="keyword">class</span> <a id="t:MonadTrans" class="def">MonadTrans</a> t <span class="keyword">where</span> <a href="#t:MonadTrans" class="selflink">#</a></p><div class="doc"><p>The class of monad transformers. Instances should satisfy the
|
||
|
|
following laws, which state that <code><a href="SafePrelude.html#v:lift">lift</a></code> is a monad transformation:</p><ul><li><pre><code><a href="SafePrelude.html#v:lift">lift</a></code> . <code><a href="SafePrelude.html#v:return">return</a></code> = <code><a href="SafePrelude.html#v:return">return</a></code></pre></li><li><pre><code><a href="SafePrelude.html#v:lift">lift</a></code> (m >>= f) = <code><a href="SafePrelude.html#v:lift">lift</a></code> m >>= (<code><a href="SafePrelude.html#v:lift">lift</a></code> . f)</pre></li></ul></div><div class="subs instances"><p id="control.i:MonadTrans" class="caption collapser" onclick="toggleSection('i:MonadTrans')">Instances</p><div id="section.i:MonadTrans" class="show"><table><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:MonadTrans:MonadTrans:1" class="instance expander" onclick="toggleSection('i:ic:MonadTrans:MonadTrans:1')"></span> <a href="SafePrelude.html#t:MonadTrans">MonadTrans</a> (<a href="../mtl-2.2.1/Control-Monad-Error.html#t:ErrorT">ErrorT</a> e)</span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:MonadTrans:MonadTrans:1" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:lift">lift</a> :: <a href="SafePrelude.html#t:Monad">Monad</a> m => m a -> <a href="../mtl-2.2.1/Control-Monad-Error.html#t:ErrorT">ErrorT</a> e m a <a href="#v:lift" class="selflink">#</a></p></div></div></td></tr></table></div></div></div><div class="top"><p class="src"><span class="keyword">class</span> <a href="SafePrelude.html#t:Monad">Monad</a> m => <a id="t:MonadReader" class="def">MonadReader</a> r m | m -> r <span class="keyword">where</span> <a href="#t:MonadReader" class="selflink">#</a></p><div class="doc"><p>See examples in <a href="../mtl-2.2.1/Control-Monad-Reader.html">Control.Monad.Reader</a>.
|
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|
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Note, the partially applied function type <code>(->) r</code> is a simple reader monad.
|
||
|
|
See the <code>instance</code> declaration below.</p></div><div class="subs minimal"><p class="caption">Minimal complete definition</p><p class="src">(<a href="SafePrelude.html#v:ask">ask</a> | <a href="SafePrelude.html#v:reader">reader</a>), <a href="SafePrelude.html#v:local">local</a></p></div><div class="subs instances"><p id="control.i:MonadReader" class="caption collapser" onclick="toggleSection('i:MonadReader')">Instances</p><div id="section.i:MonadReader" class="show"><table><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:MonadReader:MonadReader:1" class="instance expander" onclick="toggleSection('i:ic:MonadReader:MonadReader:1')"></span> <a href="SafePrelude.html#t:MonadReader">MonadReader</a> r m => <a href="SafePrelude.html#t:MonadReader">MonadReader</a> r (<a href="../transformers-0.5.2.0/Control-Monad-Trans-Maybe.html#t:MaybeT">MaybeT</a> m)</span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:MonadReader:MonadReader:1" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:ask">ask</a> :: <a href="../transformers-0.5.2.0/Control-Monad-Trans-Maybe.html#t:MaybeT">MaybeT</a> m r <a href="#v:ask" class="selflink">#</a></p><p class="src"><a href="#v:local">local</a> :: (r -> r) -> <a href="../transformers-0.5.2.0/Control-Monad-Trans-Maybe.html#t:MaybeT">MaybeT</a> m a -> <a href="../transformers-0.5.2.0/Control-Monad-Trans-Maybe.html#t:MaybeT">MaybeT</a> m a <a href="#v:local" class="selflink">#</a></p><p class="src"><a href="#v:reader">reader</a> :: (r -> a) -> <a href="../transformers-0.5.2.0/Control-Monad-Trans-Maybe.html#t:MaybeT">MaybeT</a> m a <a href="#v:reader" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:MonadReader:MonadReader:2" class="instance expander" onclick="toggleSection('i:ic:MonadReader:MonadReader:2')"></span> <a href="SafePrelude.html#t:MonadReader">MonadReader</a> r m => <a href="SafePrelude.html#t:MonadReader">MonadReader</a> r (<a href="../mtl-2.2.1/Control-Monad-List.html#t:ListT">ListT</a> m)</span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:MonadReader:MonadReader:2" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:ask">ask</a> :: <a href="../mtl-2.2.1/Control-Monad-List.html#t:ListT">ListT</a> m r <a href="#v:ask" class="selflink">#</a></p><p class="src"><a href="#v:local">local</a> :: (r -> r) -> <a href="../mtl-2.2.1/Control-Monad-List.html#t:ListT">ListT</a> m a -> <a href="../mtl-2.2.1/Control-Monad-List.html#t:ListT">ListT</a> m a <a href="#v:local" class="selflink">#</a></p><p class="src"><a href="#v:reader">reader</a> :: (r -> a) -> <a href="../mtl-2.2.1/Control-Monad-List.html#t:ListT">ListT</a> m a <a href="#v:reader" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:MonadReader:MonadReader:3" class="instance expander" onclick="toggleSection('i:ic:MonadReader:MonadReader:3')"></span> <a href="SafePrelude.html#t:MonadReader">MonadReader</a> r ((->) r)</span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:MonadReader:MonadReader:3" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:ask">ask</a> :: r -> r <a href="#v:ask" class="selflink">#</a></p><p class="src"><a href="#v:local">local</a> :: (r -> r) -> (r -> a) -> r -> a <a href="#v:local" class="selflink">#</a></p><p class="src"><a href="#v:reader">reader</a> :: (r -> a) -> r -> a <a href="#v:reader" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:MonadReader:MonadReader:4" class="instance expander" onclick="toggleSection('i:ic:MonadReader:MonadReader:4')"></span> (<a href="SafePrelude.html#t:Monoid">Monoid</a> w, <a href="Sa
|
||
|
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computation.</p></div><div class="subs minimal"><p class="caption">Minimal complete definition</p><p class="src"><a href="../exceptions-0.8.3/Control-Monad-Catch.html#v:throwM">throwM</a></p></div><div class="subs instances"><p id="control.i:MonadThrow" class="caption collapser" onclick="toggleSection('i:MonadThrow')">Instances</p><div id="section.i:MonadThrow" class="show"><table><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:MonadThrow:MonadThrow:1" class="instance expander" onclick="toggleSection('i:ic:MonadThrow:MonadThrow:1')"></span> <a href="SafePrelude.html#t:MonadThrow">MonadThrow</a> []</span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:MonadThrow:MonadThrow:1" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:throwM">throwM</a> :: <a href="SafePrelude.html#t:Exception">Exception</a> e => e -> [a] <a href="#v:throwM" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:MonadThrow:MonadThrow:2" class="instance expander" onclick="toggleSection('i:ic:MonadThrow:MonadThrow:2')"></span> <a href="SafePrelude.html#t:MonadThrow">MonadThrow</a> <a href="SafePrelude.html#t:Maybe">Maybe</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:MonadThrow:MonadThrow:2" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:throwM">throwM</a> :: <a href="SafePrelude.html#t:Exception">Exception</a> e => e -> <a href="SafePrelude.html#t:Maybe">Maybe</a> a <a href="#v:throwM" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:MonadThrow:MonadThrow:3" class="instance expander" onclick="toggleSection('i:ic:MonadThrow:MonadThrow:3')"></span> <a href="SafePrelude.html#t:MonadThrow">MonadThrow</a> <a href="SafePrelude.html#t:IO">IO</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:MonadThrow:MonadThrow:3" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:throwM">throwM</a> :: <a href="SafePrelude.html#t:Exception">Exception</a> e => e -> <a href="SafePrelude.html#t:IO">IO</a> a <a href="#v:throwM" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:MonadThrow:MonadThrow:4" class="instance expander" onclick="toggleSection('i:ic:MonadThrow:MonadThrow:4')"></span> <a href="SafePrelude.html#t:MonadThrow">MonadThrow</a> <a href="../template-haskell-2.11.0.0/Language-Haskell-TH-Syntax.html#t:Q">Q</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:MonadThrow:MonadThrow:4" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:throwM">throwM</a> :: <a href="SafePrelude.html#t:Exception">Exception</a> e => e -> <a href="../template-haskell-2.11.0.0/Language-Haskell-TH-Syntax.html#t:Q">Q</a> a <a href="#v:throwM" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:MonadThrow:MonadThrow:5" class="instance expander" onclick="toggleSection('i:ic:MonadThrow:MonadThrow:5')"></span> <a href="SafePrelude.html#t:MonadThrow">MonadThrow</a> <a href="../base-4.9.0.0/GHC-Conc.html#t:STM">STM</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:MonadThrow:MonadThrow:5" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:throwM">throwM</a> :: <a href="SafePrelude.html#t:Exception">Exception</a> e => e -> <a href="../base-4.9.0.0/GHC-Conc.html#t:STM">STM</a> a <a href="#v:throwM" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:MonadThrow:MonadThrow:6" class=
|
||
|
|
instance of the <code>Exception</code> class. The simplest case is a new exception
|
||
|
|
type directly below the root:</p><pre>data MyException = ThisException | ThatException
|
||
|
|
deriving (Show, Typeable)
|
||
|
|
|
||
|
|
instance Exception MyException</pre><p>The default method definitions in the <code>Exception</code> class do what we need
|
||
|
|
in this case. You can now throw and catch <code>ThisException</code> and
|
||
|
|
<code>ThatException</code> as exceptions:</p><pre>*Main> throw ThisException `catch` \e -> putStrLn ("Caught " ++ show (e :: MyException))
|
||
|
|
Caught ThisException
|
||
|
|
</pre><p>In more complicated examples, you may wish to define a whole hierarchy
|
||
|
|
of exceptions:</p><pre>---------------------------------------------------------------------
|
||
|
|
-- Make the root exception type for all the exceptions in a compiler
|
||
|
|
|
||
|
|
data SomeCompilerException = forall e . Exception e => SomeCompilerException e
|
||
|
|
deriving Typeable
|
||
|
|
|
||
|
|
instance Show SomeCompilerException where
|
||
|
|
show (SomeCompilerException e) = show e
|
||
|
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|
||
|
|
instance Exception SomeCompilerException
|
||
|
|
|
||
|
|
compilerExceptionToException :: Exception e => e -> SomeException
|
||
|
|
compilerExceptionToException = toException . SomeCompilerException
|
||
|
|
|
||
|
|
compilerExceptionFromException :: Exception e => SomeException -> Maybe e
|
||
|
|
compilerExceptionFromException x = do
|
||
|
|
SomeCompilerException a <- fromException x
|
||
|
|
cast a
|
||
|
|
|
||
|
|
---------------------------------------------------------------------
|
||
|
|
-- Make a subhierarchy for exceptions in the frontend of the compiler
|
||
|
|
|
||
|
|
data SomeFrontendException = forall e . Exception e => SomeFrontendException e
|
||
|
|
deriving Typeable
|
||
|
|
|
||
|
|
instance Show SomeFrontendException where
|
||
|
|
show (SomeFrontendException e) = show e
|
||
|
|
|
||
|
|
instance Exception SomeFrontendException where
|
||
|
|
toException = compilerExceptionToException
|
||
|
|
fromException = compilerExceptionFromException
|
||
|
|
|
||
|
|
frontendExceptionToException :: Exception e => e -> SomeException
|
||
|
|
frontendExceptionToException = toException . SomeFrontendException
|
||
|
|
|
||
|
|
frontendExceptionFromException :: Exception e => SomeException -> Maybe e
|
||
|
|
frontendExceptionFromException x = do
|
||
|
|
SomeFrontendException a <- fromException x
|
||
|
|
cast a
|
||
|
|
|
||
|
|
---------------------------------------------------------------------
|
||
|
|
-- Make an exception type for a particular frontend compiler exception
|
||
|
|
|
||
|
|
data MismatchedParentheses = MismatchedParentheses
|
||
|
|
deriving (Typeable, Show)
|
||
|
|
|
||
|
|
instance Exception MismatchedParentheses where
|
||
|
|
toException = frontendExceptionToException
|
||
|
|
fromException = frontendExceptionFromException</pre><p>We can now catch a <code>MismatchedParentheses</code> exception as
|
||
|
|
<code>MismatchedParentheses</code>, <code>SomeFrontendException</code> or
|
||
|
|
<code>SomeCompilerException</code>, but not other types, e.g. <code>IOException</code>:</p><pre>*Main> throw MismatchedParentheses <code>catch</code> e -> putStrLn ("Caught " ++ show (e :: MismatchedParentheses))
|
||
|
|
Caught MismatchedParentheses
|
||
|
|
*Main> throw MismatchedParentheses <code>catch</code> e -> putStrLn ("Caught " ++ show (e :: SomeFrontendException))
|
||
|
|
Caught MismatchedParentheses
|
||
|
|
*Main> throw MismatchedParentheses <code>catch</code> e -> putStrLn ("Caught " ++ show (e :: SomeCompilerException))
|
||
|
|
Caught MismatchedParentheses
|
||
|
|
*Main> throw MismatchedParentheses <code>catch</code> e -> putStrLn ("Caught " ++ show (e :: IOException))
|
||
|
|
*** Exception: MismatchedParentheses
|
||
|
|
</pre></div><div class="subs minimal"><p class="caption">Minimal complete definition</p><p class="src">Nothing</p></div><div class="subs instances"><p id="control.i:Exception" class="caption collapser" onclick="toggleSection('i:Exception')">Instances</p><div id="section.i:Exception" class="show"><table><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Exception:Exception:1" class="instance expander" onclick="toggleSection('i:ic:Exception:Exception:1')"></span> <a href="SafePrelude.html#t:Exception">Exception</a> <a href="../base-4.9.0.0/Data-Void.html#t:Void">Void</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:Exception:Exception:1" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:toException">toException</a> :: <a href="../base-4.9.0.0/Data-Void.html#t:Void">Void</a> -> <a href="SafePrelude.html#t:SomeException">SomeException</a> <a href="#v:toException" class="selflink">#</a></p><p class="src"><a href="#v:fromException">fromException</a> :: <a href="SafePrelude.html#t:SomeException">SomeException</a> -> <a href="SafePrelude.html#t:Maybe">Maybe</a> <a href="../base-4.9.0.0/Data-Void.html#t:Void">Void</a> <a href="#v:fromException" class="selflink">#</a></p><p class="src"><a href="#v:displayException">displayException</a> :: <a href="../base-4.9.0.0/Data-Void.html#t:Void">Void</a> -> <a href="SafePrelude.html#t:String">String</a> <a href="#v:displayException" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Exception:Exception:2" class="instance expander" onclick="toggleSection('i:ic:Exception:Exception:2')"></span> <a href="SafePrelude.html#t:Exception">Exception</a> <a href="../base-4.9.0.0/Control-Exception-Base.html#t:BlockedIndefinitelyOnMVar">BlockedIndefinitelyOnMVar</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:Exception:Exception:2" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:toException">toException</a> :: <a href="../base-4.9.0.0/Control-Exception-Base.html#t:BlockedIndefinitelyOnMVar">BlockedIndefinitelyOnMVar</a> -> <a href="SafePrelude.html#t:SomeException">SomeException</a> <a href="#v:toException" class="selflink">#</a></p><p class="src"><a href="#v:fromException">fromException</a> :: <a href="SafePrelude.html#t:SomeException">SomeException</a> -> <a href="SafePrelude.html#t:Maybe">Maybe</a> <a href="../base-4.9.0.0/Control-Exception-Base.html#t:BlockedIndefinitelyOnMVar">BlockedIndefinitelyOnMVar</a> <a href="#v:fromException" class="selflink">#</a></p><p class="src"><a href="#v:displayException">displayException</a> :: <a href="../base-4.9.0.0/Control-Exception-Base.html#t:BlockedIndefinitelyOnMVar">BlockedIndefinitelyOnMVar</a> -> <a href="SafePrelude.html#t:String">String</a> <a href="#v:displayException" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Exception:Exception:3" class="instance expander" onclick="toggleSection('i:ic:Exception:Exception:3')"></span> <a href="SafePrelude.html#t:Exception">Exception</a> <a href="../base-4.9.0.0/Control-Exception-Base.html#t:BlockedIndefinitelyOnSTM">BlockedIndefinitelyOnSTM</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:Exception:Exception:3" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:toException">toException</a> :: <a href="../base-4.9.0.0/Control-Exception-Base.html#t:BlockedIndefinitelyOnSTM">BlockedIndefinitelyOnSTM</a> -> <a href="SafePrelude.html#t:SomeException">SomeException</a> <a href="#v:toException" class="selflink">#</a></p><p class="src"><a href="#v:fromException">fromException</a> :: <a href="SafePrelude.html#t:SomeException">SomeException</a> -> <a href="SafePrelude.html#t:Maybe">Maybe</a> <a href="../base-4.9.0.0/
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||
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exceptions which were thrown by <code><a href="../exceptions-0.8.3/Control-Monad-Catch.html#v:throwM">throwM</a></code>.</p><p>Instances should obey the following law:</p><pre>catch (throwM e) f = f e</pre><p>Note that the ability to catch an exception does <em>not</em> guarantee that we can
|
||
|
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deal with all possible exit points from a computation. Some monads, such as
|
||
|
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continuation-based stacks, allow for more than just a success/failure
|
||
|
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strategy, and therefore <code>catch</code> <em>cannot</em> be used by those monads to properly
|
||
|
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implement a function such as <code>finally</code>. For more information, see
|
||
|
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<code><a href="SafePrelude.html#t:MonadMask">MonadMask</a></code>.</p></div><div class="subs minimal"><p class="caption">Minimal complete definition</p><p class="src"><a href="../exceptions-0.8.3/Control-Monad-Catch.html#v:catch">catch</a></p></div><div class="subs instances"><p id="control.i:MonadCatch" class="caption collapser" onclick="toggleSection('i:MonadCatch')">Instances</p><div id="section.i:MonadCatch" class="show"><table><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:MonadCatch:MonadCatch:1" class="instance expander" onclick="toggleSection('i:ic:MonadCatch:MonadCatch:1')"></span> <a href="SafePrelude.html#t:MonadCatch">MonadCatch</a> <a href="SafePrelude.html#t:IO">IO</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:MonadCatch:MonadCatch:1" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:catch">catch</a> :: <a href="SafePrelude.html#t:Exception">Exception</a> e => <a href="SafePrelude.html#t:IO">IO</a> a -> (e -> <a href="SafePrelude.html#t:IO">IO</a> a) -> <a href="SafePrelude.html#t:IO">IO</a> a <a href="#v:catch" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:MonadCatch:MonadCatch:2" class="instance expander" onclick="toggleSection('i:ic:MonadCatch:MonadCatch:2')"></span> <a href="SafePrelude.html#t:MonadCatch">MonadCatch</a> <a href="../base-4.9.0.0/GHC-Conc.html#t:STM">STM</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:MonadCatch:MonadCatch:2" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:catch">catch</a> :: <a href="SafePrelude.html#t:Exception">Exception</a> e => <a href="../base-4.9.0.0/GHC-Conc.html#t:STM">STM</a> a -> (e -> <a href="../base-4.9.0.0/GHC-Conc.html#t:STM">STM</a> a) -> <a href="../base-4.9.0.0/GHC-Conc.html#t:STM">STM</a> a <a href="#v:catch" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:MonadCatch:MonadCatch:3" class="instance expander" onclick="toggleSection('i:ic:MonadCatch:MonadCatch:3')"></span> (~) <a href="../base-4.9.0.0/Data-Kind.html#t:-42-">*</a> e <a href="SafePrelude.html#t:SomeException">SomeException</a> => <a href="SafePrelude.html#t:MonadCatch">MonadCatch</a> (<a href="SafePrelude.html#t:Either">Either</a> e)</span></td><td class="doc"><p><em>Since: 0.8.3</em></p></td></tr><tr><td colspan="2"><div id="section.i:ic:MonadCatch:MonadCatch:3" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:catch">catch</a> :: <a href="SafePrelude.html#t:Exception">Exception</a> e => <a href="SafePrelude.html#t:Either">Either</a> e a -> (e -> <a href="SafePrelude.html#t:Either">Either</a> e a) -> <a href="SafePrelude.html#t:Either">Either</a> e a <a href="#v:catch" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:MonadCatch:MonadCatch:4" class="instance expander" onclick="toggleSection('i:ic:MonadCatch:MonadCatch:4')"></span> <a href="SafePrelude.html#t:MonadCatch">MonadCatch</a> m => <a href="SafePrelude.html#t:MonadCatch">MonadCatch</a> (<a href="../mtl-2.2.1/Control-Monad-List.html#t:ListT">ListT</a> m)</span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:MonadCatch:MonadCatch:4" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:catch">catch</a> :: <a href="SafePrelude.html#t:Exception">Exception</a> e => <a href="../mtl-2.2.1/Control-Monad-List.html#t:ListT">ListT</a> m a -> (e -> <a href="../mtl-2.2.1/Control-Monad-List.html#t:ListT">ListT</a> m a) -> <a href="../mtl-2.2.1/Control-Monad-List.html#t:ListT">ListT</a> m a <a href="#v:catch" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clear
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||
|
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possible exit points from a computation, and to mask asynchronous
|
||
|
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exceptions. Continuation-based monads, and stacks such as <code>ErrorT e IO</code>
|
||
|
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which provide for multiple failure modes, are invalid instances of this
|
||
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class.</p><p>Note that this package <em>does</em> provide a <code>MonadMask</code> instance for <code>CatchT</code>.
|
||
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This instance is <em>only</em> valid if the base monad provides no ability to
|
||
|
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provide multiple exit. For example, <code>IO</code> or <code>Either</code> would be invalid base
|
||
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monads, but <code>Reader</code> or <code>State</code> would be acceptable.</p><p>Instances should ensure that, in the following code:</p><pre>f `finally` g</pre><p>The action <code>g</code> is called regardless of what occurs within <code>f</code>, including
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|
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async exceptions.</p></div><div class="subs minimal"><p class="caption">Minimal complete definition</p><p class="src"><a href="../exceptions-0.8.3/Control-Monad-Catch.html#v:mask">mask</a>, <a href="../exceptions-0.8.3/Control-Monad-Catch.html#v:uninterruptibleMask">uninterruptibleMask</a></p></div><div class="subs instances"><p id="control.i:MonadMask" class="caption collapser" onclick="toggleSection('i:MonadMask')">Instances</p><div id="section.i:MonadMask" class="show"><table><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:MonadMask:MonadMask:1" class="instance expander" onclick="toggleSection('i:ic:MonadMask:MonadMask:1')"></span> <a href="SafePrelude.html#t:MonadMask">MonadMask</a> <a href="SafePrelude.html#t:IO">IO</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:MonadMask:MonadMask:1" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:mask">mask</a> :: ((<span class="keyword">forall</span> a. <a href="SafePrelude.html#t:IO">IO</a> a -> <a href="SafePrelude.html#t:IO">IO</a> a) -> <a href="SafePrelude.html#t:IO">IO</a> b) -> <a href="SafePrelude.html#t:IO">IO</a> b <a href="#v:mask" class="selflink">#</a></p><p class="src"><a href="#v:uninterruptibleMask">uninterruptibleMask</a> :: ((<span class="keyword">forall</span> a. <a href="SafePrelude.html#t:IO">IO</a> a -> <a href="SafePrelude.html#t:IO">IO</a> a) -> <a href="SafePrelude.html#t:IO">IO</a> b) -> <a href="SafePrelude.html#t:IO">IO</a> b <a href="#v:uninterruptibleMask" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:MonadMask:MonadMask:2" class="instance expander" onclick="toggleSection('i:ic:MonadMask:MonadMask:2')"></span> (~) <a href="../base-4.9.0.0/Data-Kind.html#t:-42-">*</a> e <a href="SafePrelude.html#t:SomeException">SomeException</a> => <a href="SafePrelude.html#t:MonadMask">MonadMask</a> (<a href="SafePrelude.html#t:Either">Either</a> e)</span></td><td class="doc"><p><em>Since: 0.8.3</em></p></td></tr><tr><td colspan="2"><div id="section.i:ic:MonadMask:MonadMask:2" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:mask">mask</a> :: ((<span class="keyword">forall</span> a. <a href="SafePrelude.html#t:Either">Either</a> e a -> <a href="SafePrelude.html#t:Either">Either</a> e a) -> <a href="SafePrelude.html#t:Either">Either</a> e b) -> <a href="SafePrelude.html#t:Either">Either</a> e b <a href="#v:mask" class="selflink">#</a></p><p class="src"><a href="#v:uninterruptibleMask">uninterruptibleMask</a> :: ((<span class="keyword">forall</span> a. <a href="SafePrelude.html#t:Either">Either</a> e a -> <a href="SafePrelude.html#t:Either">Either</a> e a) -> <a href="SafePrelude.html#t:Either">Either</a> e b) -> <a href="SafePrelude.html#t:Either">Either</a> e b <a href="#v:uninterruptibleMask" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:MonadMask:MonadMask:3" class="instance expander" onclick="toggleSection('i:ic:MonadMask:MonadMask:3')"></span> <a href="SafePrelude.html#t:MonadMask">MonadMask</a> m => <a href="SafePrelude.html#t:MonadMask">MonadMask</a> (<a href="../mtl-2.2.1/Control-Monad-State-Lazy.html#t:StateT">StateT</a> s m)</span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:MonadMask:MonadMask:3" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:mask">mask</a> :: ((<span class="keyword">forall</span> a. <a href="../mtl-2.2.1/Control-Monad-State-Lazy.html#t:StateT">StateT</a> s m a -> <a href="../mtl-2.2.1/Control-Monad-State-Lazy.html#t:StateT">StateT</a> s m a) -> <a href="../mtl-2.2.1/Control-Monad-State-Lazy.html#t:StateT">StateT</a> s m b) -> <a href="../mtl-2.2.1/Control-Monad-State-Lazy.html#t:StateT">StateT</a> s m b <a href="#v:mask" class="selflink">#<
|
||
|
|
foldMap f Empty = mempty
|
||
|
|
foldMap f (Leaf x) = f x
|
||
|
|
foldMap f (Node l k r) = foldMap f l `mappend` f k `mappend` foldMap f r</pre><p>This is suitable even for abstract types, as the monoid is assumed
|
||
|
|
to satisfy the monoid laws. Alternatively, one could define <code>foldr</code>:</p><pre>instance Foldable Tree where
|
||
|
|
foldr f z Empty = z
|
||
|
|
foldr f z (Leaf x) = f x z
|
||
|
|
foldr f z (Node l k r) = foldr f (f k (foldr f z r)) l</pre><p><code>Foldable</code> instances are expected to satisfy the following laws:</p><pre>foldr f z t = appEndo (foldMap (Endo . f) t ) z</pre><pre>foldl f z t = appEndo (getDual (foldMap (Dual . Endo . flip f) t)) z</pre><pre>fold = foldMap id</pre><p><code>sum</code>, <code>product</code>, <code>maximum</code>, and <code>minimum</code> should all be essentially
|
||
|
|
equivalent to <code>foldMap</code> forms, such as</p><pre>sum = getSum . foldMap Sum</pre><p>but may be less defined.</p><p>If the type is also a <code><a href="SafePrelude.html#t:Functor">Functor</a></code> instance, it should satisfy</p><pre>foldMap f = fold . fmap f</pre><p>which implies that</p><pre>foldMap f . fmap g = foldMap (f . g)</pre></div><div class="subs minimal"><p class="caption">Minimal complete definition</p><p class="src"><a href="SafePrelude.html#v:foldMap">foldMap</a> | <a href="SafePrelude.html#v:foldr">foldr</a></p></div><div class="subs instances"><p id="control.i:Foldable" class="caption collapser" onclick="toggleSection('i:Foldable')">Instances</p><div id="section.i:Foldable" class="show"><table><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Foldable:Foldable:1" class="instance expander" onclick="toggleSection('i:ic:Foldable:Foldable:1')"></span> <a href="SafePrelude.html#t:Foldable">Foldable</a> []</span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:Foldable:Foldable:1" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:fold">fold</a> :: <a href="SafePrelude.html#t:Monoid">Monoid</a> m => [m] -> m <a href="#v:fold" class="selflink">#</a></p><p class="src"><a href="#v:foldMap">foldMap</a> :: <a href="SafePrelude.html#t:Monoid">Monoid</a> m => (a -> m) -> [a] -> m <a href="#v:foldMap" class="selflink">#</a></p><p class="src"><a href="#v:foldr">foldr</a> :: (a -> b -> b) -> b -> [a] -> b <a href="#v:foldr" class="selflink">#</a></p><p class="src"><a href="#v:foldr-39-">foldr'</a> :: (a -> b -> b) -> b -> [a] -> b <a href="#v:foldr-39-" class="selflink">#</a></p><p class="src"><a href="#v:foldl">foldl</a> :: (b -> a -> b) -> b -> [a] -> b <a href="#v:foldl" class="selflink">#</a></p><p class="src"><a href="#v:foldl-39-">foldl'</a> :: (b -> a -> b) -> b -> [a] -> b <a href="#v:foldl-39-" class="selflink">#</a></p><p class="src"><a href="#v:foldr1">foldr1</a> :: (a -> a -> a) -> [a] -> a <a href="#v:foldr1" class="selflink">#</a></p><p class="src"><a href="#v:foldl1">foldl1</a> :: (a -> a -> a) -> [a] -> a <a href="#v:foldl1" class="selflink">#</a></p><p class="src"><a href="#v:toList">toList</a> :: [a] -> [a] <a href="#v:toList" class="selflink">#</a></p><p class="src"><a href="#v:null">null</a> :: [a] -> <a href="SafePrelude.html#t:Bool">Bool</a> <a href="#v:null" class="selflink">#</a></p><p class="src"><a href="#v:length">length</a> :: [a] -> <a href="SafePrelude.html#t:Int">Int</a> <a href="#v:length" class="selflink">#</a></p><p class="src"><a href="#v:elem">elem</a> :: <a href="SafePrelude.html#t:Eq">Eq</a> a => a -> [a] -> <a href="SafePrelude.html#t:Bool">Bool</a> <a href="#v:elem" class="selflink">#</a></p><p class="src"><a href="#v:maximum">maximum</a> :: <a href="SafePrelude.html#t:Ord">Ord</a> a => [a] -> a <a href="#v:maximum" class="selflink">#</a></p><p class="src"><a href="#v:minimum">minimum</a> :: <a href="SafePrelude.html#t:Ord">Ord</a> a => [a] -> a <a href="#v:minimum" class="selflink">#</a></p><p class="src"><a href="#v:sum">sum</a> :: <a href="SafePrelude.html#t:Num">Num</a> a => [a] -> a <a href="#v:sum" class="selflink">#</a></p><p class="src"><a href="#v:product">product</a> :: <a href="SafePrelude.html#t:Num">Num</a> a => [a] -> a <a href="#v:product" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Foldable:Foldable:2" class="instance expander" onclick="toggleSection('i:ic:Foldable:Foldable:2')"></span> <a href="SafePrelude.html#t:Foldable">Foldable</a> <a href="SafePrelude.html#t:Maybe">Maybe</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:Foldable:Foldable:2" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:fold">fold</a> ::
|
||
|
|
optimized for structures that are similar to cons-lists, because there
|
||
|
|
is no general way to do better.</p></div></div><div class="top"><p class="src"><a id="v:length" class="def">length</a> :: <a href="SafePrelude.html#t:Foldable">Foldable</a> t => <span class="keyword">forall</span> a. t a -> <a href="SafePrelude.html#t:Int">Int</a> <a href="#v:length" class="selflink">#</a></p><div class="doc"><p>Returns the size/length of a finite structure as an <code><a href="SafePrelude.html#t:Int">Int</a></code>. The
|
||
|
|
default implementation is optimized for structures that are similar to
|
||
|
|
cons-lists, because there is no general way to do better.</p></div></div><div class="top"><p class="src"><a id="v:elem" class="def">elem</a> :: <a href="SafePrelude.html#t:Foldable">Foldable</a> t => <span class="keyword">forall</span> a. <a href="SafePrelude.html#t:Eq">Eq</a> a => a -> t a -> <a href="SafePrelude.html#t:Bool">Bool</a> <a href="#v:elem" class="selflink">#</a></p><div class="doc"><p>Does the element occur in the structure?</p></div></div><div class="top"><p class="src"><span class="keyword">class</span> (<a href="SafePrelude.html#t:Functor">Functor</a> t, <a href="SafePrelude.html#t:Foldable">Foldable</a> t) => <a id="t:Traversable" class="def">Traversable</a> t <span class="keyword">where</span> <a href="#t:Traversable" class="selflink">#</a></p><div class="doc"><p>Functors representing data structures that can be traversed from
|
||
|
|
left to right.</p><p>A definition of <code><a href="SafePrelude.html#v:traverse">traverse</a></code> must satisfy the following laws:</p><dl><dt><em>naturality</em></dt><dd><code>t . <code><a href="SafePrelude.html#v:traverse">traverse</a></code> f = <code><a href="SafePrelude.html#v:traverse">traverse</a></code> (t . f)</code>
|
||
|
|
for every applicative transformation <code>t</code></dd><dt><em>identity</em></dt><dd><code><code><a href="SafePrelude.html#v:traverse">traverse</a></code> Identity = Identity</code></dd><dt><em>composition</em></dt><dd><code><code><a href="SafePrelude.html#v:traverse">traverse</a></code> (Compose . <code><a href="SafePrelude.html#v:fmap">fmap</a></code> g . f) = Compose . <code><a href="SafePrelude.html#v:fmap">fmap</a></code> (<code><a href="SafePrelude.html#v:traverse">traverse</a></code> g) . <code><a href="SafePrelude.html#v:traverse">traverse</a></code> f</code></dd></dl><p>A definition of <code><a href="SafePrelude.html#v:sequenceA">sequenceA</a></code> must satisfy the following laws:</p><dl><dt><em>naturality</em></dt><dd><code>t . <code><a href="SafePrelude.html#v:sequenceA">sequenceA</a></code> = <code><a href="SafePrelude.html#v:sequenceA">sequenceA</a></code> . <code><a href="SafePrelude.html#v:fmap">fmap</a></code> t</code>
|
||
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for every applicative transformation <code>t</code></dd><dt><em>identity</em></dt><dd><code><code><a href="SafePrelude.html#v:sequenceA">sequenceA</a></code> . <code><a href="SafePrelude.html#v:fmap">fmap</a></code> Identity = Identity</code></dd><dt><em>composition</em></dt><dd><code><code><a href="SafePrelude.html#v:sequenceA">sequenceA</a></code> . <code><a href="SafePrelude.html#v:fmap">fmap</a></code> Compose = Compose . <code><a href="SafePrelude.html#v:fmap">fmap</a></code> <code><a href="SafePrelude.html#v:sequenceA">sequenceA</a></code> . <code><a href="SafePrelude.html#v:sequenceA">sequenceA</a></code></code></dd></dl><p>where an <em>applicative transformation</em> is a function</p><pre>t :: (Applicative f, Applicative g) => f a -> g a</pre><p>preserving the <code><a href="SafePrelude.html#t:Applicative">Applicative</a></code> operations, i.e.</p><ul><li><pre>t (<code><a href="SafePrelude.html#v:pure">pure</a></code> x) = <code><a href="SafePrelude.html#v:pure">pure</a></code> x</pre></li><li><pre>t (x <code><a href="SafePrelude.html#v:-60--42--62-"><*></a></code> y) = t x <code><a href="SafePrelude.html#v:-60--42--62-"><*></a></code> t y</pre></li></ul><p>and the identity functor <code>Identity</code> and composition of functors <code>Compose</code>
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are defined as</p><pre> newtype Identity a = Identity a
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instance Functor Identity where
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fmap f (Identity x) = Identity (f x)
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instance Applicative Identity where
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pure x = Identity x
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Identity f <*> Identity x = Identity (f x)
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newtype Compose f g a = Compose (f (g a))
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instance (Functor f, Functor g) => Functor (Compose f g) where
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fmap f (Compose x) = Compose (fmap (fmap f) x)
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instance (Applicative f, Applicative g) => Applicative (Compose f g) where
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pure x = Compose (pure (pure x))
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Compose f <*> Compose x = Compose ((<*>) <$> f <*> x)</pre><p>(The naturality law is implied by parametricity.)</p><p>Instances are similar to <code><a href="SafePrelude.html#t:Functor">Functor</a></code>, e.g. given a data type</p><pre>data Tree a = Empty | Leaf a | Node (Tree a) a (Tree a)</pre><p>a suitable instance would be</p><pre>instance Traversable Tree where
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traverse f Empty = pure Empty
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traverse f (Leaf x) = Leaf <$> f x
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traverse f (Node l k r) = Node <$> traverse f l <*> f k <*> traverse f r</pre><p>This is suitable even for abstract types, as the laws for <code><a href="SafePrelude.html#v:-60--42--62-"><*></a></code>
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imply a form of associativity.</p><p>The superclass instances should satisfy the following:</p><ul><li>In the <code><a href="SafePrelude.html#t:Functor">Functor</a></code> instance, <code><a href="SafePrelude.html#v:fmap">fmap</a></code> should be equivalent to traversal
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with the identity applicative functor (<code><a href="../base-4.9.0.0/Data-Traversable.html#v:fmapDefault">fmapDefault</a></code>).</li><li>In the <code><a href="SafePrelude.html#t:Foldable">Foldable</a></code> instance, <code><a href="../base-4.9.0.0/Data-Foldable.html#v:foldMap">foldMap</a></code> should be
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equivalent to traversal with a constant applicative functor
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(<code><a href="../base-4.9.0.0/Data-Traversable.html#v:foldMapDefault">foldMapDefault</a></code>).</li></ul></div><div class="subs minimal"><p class="caption">Minimal complete definition</p><p class="src"><a href="SafePrelude.html#v:traverse">traverse</a> | <a href="SafePrelude.html#v:sequenceA">sequenceA</a></p></div><div class="subs instances"><p id="control.i:Traversable" class="caption collapser" onclick="toggleSection('i:Traversable')">Instances</p><div id="section.i:Traversable" class="show"><table><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Traversable:Traversable:1" class="instance expander" onclick="toggleSection('i:ic:Traversable:Traversable:1')"></span> <a href="SafePrelude.html#t:Traversable">Traversable</a> []</span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:Traversable:Traversable:1" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:traverse">traverse</a> :: <a href="SafePrelude.html#t:Applicative">Applicative</a> f => (a -> f b) -> [a] -> f [b] <a href="#v:traverse" class="selflink">#</a></p><p class="src"><a href="#v:sequenceA">sequenceA</a> :: <a href="SafePrelude.html#t:Applicative">Applicative</a> f => [f a] -> f [a] <a href="#v:sequenceA" class="selflink">#</a></p><p class="src"><a href="#v:mapM">mapM</a> :: <a href="SafePrelude.html#t:Monad">Monad</a> m => (a -> m b) -> [a] -> m [b] <a href="#v:mapM" class="selflink">#</a></p><p class="src"><a href="#v:sequence">sequence</a> :: <a href="SafePrelude.html#t:Monad">Monad</a> m => [m a] -> m [a] <a href="#v:sequence" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Traversable:Traversable:2" class="instance expander" onclick="toggleSection('i:ic:Traversable:Traversable:2')"></span> <a href="SafePrelude.html#t:Traversable">Traversable</a> <a href="SafePrelude.html#t:Maybe">Maybe</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:Traversable:Traversable:2" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:traverse">traverse</a> :: <a href="SafePrelude.html#t:Applicative">Applicative</a> f => (a -> f b) -> <a href="SafePrelude.html#t:Maybe">Maybe</a> a -> f (<a href="SafePrelude.html#t:Maybe">Maybe</a> b) <a href="#v:traverse" class="selflink">#</a></p><p class="src"><a href="#v:sequenceA">sequenceA</a> :: <a href="SafePrelude.html#t:Applicative">Applicative</a> f => <a href="SafePrelude.html#t:Maybe">Maybe</a> (f a) -> f (<a href="SafePrelude.html#t:Maybe">Maybe</a> a) <a href="#v:sequenceA" class="selflink">#</a></p><p class="src"><a href="#v:mapM">mapM</a> :: <a href="SafePrelude.html#t:Monad">Monad</a> m => (a -> m b) -> <a href="SafePrelude.html#t:Maybe">Maybe</a> a -> m (<a href="SafePrelude.html#t:Maybe">Maybe</a> b) <a href="#v:mapM" class="selflink">#</a></p><p class="src"><a href="#v:sequence">sequence</a> :: <a href="SafePrelude.html#t:Monad">Monad</a> m => <a href="SafePrelude.html#t:Maybe">Maybe</a> (m a) -> m (<a href="SafePrelude.html#t:Maybe">Maybe</a> a) <a href="#v:sequence" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Traversable:Traversable:3" class="instance expander" onclick="toggleSection('i:ic:Traversable:Traversable:3')"></span> <a href="SafePrelude.html#t:Traversable">Traversable</a> <a href="../base-4.9.0.0/GHC-Generics.html#t:V1">V1</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:Traversable:Traversable:3" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:traverse">traverse</a> :: <a href="SafePrelude.html#t:Applicative">Applicative</a> f => (a -> f b) -> <a href="../base-4.9.0.0/GHC-Generics.html#t:V1">V1</a> a -> f (<a href="../base-4.9.0.0/GHC-Generics
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be calculated.</p></div><div class="subs minimal"><p class="caption">Minimal complete definition</p><p class="src"><a href="../base-4.9.0.0/Data-Typeable-Internal.html#v:typeRep-35-">typeRep#</a></p></div></div><div class="top"><p class="src"><span class="keyword">class</span> <a id="t:IsString" class="def">IsString</a> a <span class="keyword">where</span> <a href="#t:IsString" class="selflink">#</a></p><div class="doc"><p>Class for string-like datastructures; used by the overloaded string
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extension (-XOverloadedStrings in GHC).</p></div><div class="subs instances"><p id="control.i:IsString" class="caption collapser" onclick="toggleSection('i:IsString')">Instances</p><div id="section.i:IsString" class="show"><table><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:IsString:IsString:1" class="instance expander" onclick="toggleSection('i:ic:IsString:IsString:1')"></span> <a href="SafePrelude.html#t:IsString">IsString</a> <a href="SafePrelude.html#t:ByteString">ByteString</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:IsString:IsString:1" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:fromString">fromString</a> :: <a href="SafePrelude.html#t:String">String</a> -> <a href="SafePrelude.html#t:ByteString">ByteString</a> <a href="#v:fromString" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:IsString:IsString:2" class="instance expander" onclick="toggleSection('i:ic:IsString:IsString:2')"></span> (~) <a href="../base-4.9.0.0/Data-Kind.html#t:-42-">*</a> a <a href="SafePrelude.html#t:Char">Char</a> => <a href="SafePrelude.html#t:IsString">IsString</a> [a]</span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:IsString:IsString:2" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:fromString">fromString</a> :: <a href="SafePrelude.html#t:String">String</a> -> [a] <a href="#v:fromString" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:IsString:IsString:3" class="instance expander" onclick="toggleSection('i:ic:IsString:IsString:3')"></span> <a href="SafePrelude.html#t:IsString">IsString</a> a => <a href="SafePrelude.html#t:IsString">IsString</a> (<a href="SafePrelude.html#t:Identity">Identity</a> a)</span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:IsString:IsString:3" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:fromString">fromString</a> :: <a href="SafePrelude.html#t:String">String</a> -> <a href="SafePrelude.html#t:Identity">Identity</a> a <a href="#v:fromString" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:IsString:IsString:4" class="instance expander" onclick="toggleSection('i:ic:IsString:IsString:4')"></span> <a href="SafePrelude.html#t:IsString">IsString</a> (<a href="SafePrelude.html#t:Seq">Seq</a> <a href="SafePrelude.html#t:Char">Char</a>)</span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:IsString:IsString:4" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:fromString">fromString</a> :: <a href="SafePrelude.html#t:String">String</a> -> <a href="SafePrelude.html#t:Seq">Seq</a> <a href="SafePrelude.html#t:Char">Char</a> <a href="#v:fromString" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:IsString:IsString:5" class="instance expander" onclick="toggleSection('i:ic:IsString:IsString:5')"></span> <a href="SafePrelude.html#t:IsString">IsString</a> a => <a href="SafePrelude.html#t:IsString">IsString</a> (<a href="../base-4.9.0.0/Data-Functor-Const.html#t:Const">Const</a> <a href="../base-4.9.0.0/Data-Kind.html#t:-42-">*</a> a b)</span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:IsString:IsString:5" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:fromString">fromString</a> :: <a href="SafePrelude.html#t:String">String</a> -> <a href="../base-4.9.0.0/Data-Functor-Const.html#t:Const">Const</a> <a href="../base-4.9.0.0/Data-Kind.html#t:-42-">*</a> a b <a href
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||
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has an identity). Instances should satisfy the following laws:</p><ul><li><pre>mappend mempty x = x</pre></li><li><pre>mappend x mempty = x</pre></li><li><pre>mappend x (mappend y z) = mappend (mappend x y) z</pre></li><li><pre>mconcat = <code><a href="../base-4.9.0.0/GHC-OldList.html#v:foldr">foldr</a></code> mappend mempty</pre></li></ul><p>The method names refer to the monoid of lists under concatenation,
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||
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|
but there are many other instances.</p><p>Some types can be viewed as a monoid in more than one way,
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||
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e.g. both addition and multiplication on numbers.
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||
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In such cases we often define <code>newtype</code>s and make those instances
|
||
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of <code><a href="SafePrelude.html#t:Monoid">Monoid</a></code>, e.g. <code>Sum</code> and <code>Product</code>.</p></div><div class="subs minimal"><p class="caption">Minimal complete definition</p><p class="src"><a href="SafePrelude.html#v:mempty">mempty</a>, <a href="SafePrelude.html#v:mappend">mappend</a></p></div><div class="subs instances"><p id="control.i:Monoid" class="caption collapser" onclick="toggleSection('i:Monoid')">Instances</p><div id="section.i:Monoid" class="show"><table><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Monoid:Monoid:1" class="instance expander" onclick="toggleSection('i:ic:Monoid:Monoid:1')"></span> <a href="SafePrelude.html#t:Monoid">Monoid</a> <a href="SafePrelude.html#t:Ordering">Ordering</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:Monoid:Monoid:1" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:mempty">mempty</a> :: <a href="SafePrelude.html#t:Ordering">Ordering</a> <a href="#v:mempty" class="selflink">#</a></p><p class="src"><a href="#v:mappend">mappend</a> :: <a href="SafePrelude.html#t:Ordering">Ordering</a> -> <a href="SafePrelude.html#t:Ordering">Ordering</a> -> <a href="SafePrelude.html#t:Ordering">Ordering</a> <a href="#v:mappend" class="selflink">#</a></p><p class="src"><a href="#v:mconcat">mconcat</a> :: [<a href="SafePrelude.html#t:Ordering">Ordering</a>] -> <a href="SafePrelude.html#t:Ordering">Ordering</a> <a href="#v:mconcat" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Monoid:Monoid:2" class="instance expander" onclick="toggleSection('i:ic:Monoid:Monoid:2')"></span> <a href="SafePrelude.html#t:Monoid">Monoid</a> ()</span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:Monoid:Monoid:2" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:mempty">mempty</a> :: () <a href="#v:mempty" class="selflink">#</a></p><p class="src"><a href="#v:mappend">mappend</a> :: () -> () -> () <a href="#v:mappend" class="selflink">#</a></p><p class="src"><a href="#v:mconcat">mconcat</a> :: [()] -> () <a href="#v:mconcat" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Monoid:Monoid:3" class="instance expander" onclick="toggleSection('i:ic:Monoid:Monoid:3')"></span> <a href="SafePrelude.html#t:Monoid">Monoid</a> <a href="../base-4.9.0.0/Data-Monoid.html#t:All">All</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:Monoid:Monoid:3" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:mempty">mempty</a> :: <a href="../base-4.9.0.0/Data-Monoid.html#t:All">All</a> <a href="#v:mempty" class="selflink">#</a></p><p class="src"><a href="#v:mappend">mappend</a> :: <a href="../base-4.9.0.0/Data-Monoid.html#t:All">All</a> -> <a href="../base-4.9.0.0/Data-Monoid.html#t:All">All</a> -> <a href="../base-4.9.0.0/Data-Monoid.html#t:All">All</a> <a href="#v:mappend" class="selflink">#</a></p><p class="src"><a href="#v:mconcat">mconcat</a> :: [<a href="../base-4.9.0.0/Data-Monoid.html#t:All">All</a>] -> <a href="../base-4.9.0.0/Data-Monoid.html#t:All">All</a> <a href="#v:mconcat" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Monoid:Monoid:4" class="instance expander" onclick="toggleSection('i:ic:Monoid:Monoid:4')"></span> <a href="SafePrelude.html#t:Monoid">Monoid</a> <a href="../base-4.9.0.0/Data-Monoid.html#t:Any">Any</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:Monoid:Monoid:4" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:mempty">mempty</a> :: <a href="../base-4.9.0.0/Data-Monoid.html#t:Any">Any</a> <a href="#v:me
|
||
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<a href="http://en.wikipedia.org/wiki/Monoid">http://en.wikipedia.org/wiki/Monoid</a>: "Any semigroup <code>S</code> may be
|
||
|
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turned into a monoid simply by adjoining an element <code>e</code> not in <code>S</code>
|
||
|
|
and defining <code>e*e = e</code> and <code>e*s = s = s*e</code> for all <code>s ∈ S</code>." Since
|
||
|
|
there is no "Semigroup" typeclass providing just <code><a href="SafePrelude.html#v:mappend">mappend</a></code>, we
|
||
|
|
use <code><a href="SafePrelude.html#t:Monoid">Monoid</a></code> instead.</p></td></tr><tr><td colspan="2"><div id="section.i:ic:Monoid:Monoid:8" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:mempty">mempty</a> :: <a href="SafePrelude.html#t:Maybe">Maybe</a> a <a href="#v:mempty" class="selflink">#</a></p><p class="src"><a href="#v:mappend">mappend</a> :: <a href="SafePrelude.html#t:Maybe">Maybe</a> a -> <a href="SafePrelude.html#t:Maybe">Maybe</a> a -> <a href="SafePrelude.html#t:Maybe">Maybe</a> a <a href="#v:mappend" class="selflink">#</a></p><p class="src"><a href="#v:mconcat">mconcat</a> :: [<a href="SafePrelude.html#t:Maybe">Maybe</a> a] -> <a href="SafePrelude.html#t:Maybe">Maybe</a> a <a href="#v:mconcat" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Monoid:Monoid:9" class="instance expander" onclick="toggleSection('i:ic:Monoid:Monoid:9')"></span> <a href="SafePrelude.html#t:Monoid">Monoid</a> a => <a href="SafePrelude.html#t:Monoid">Monoid</a> (<a href="SafePrelude.html#t:IO">IO</a> a)</span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:Monoid:Monoid:9" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:mempty">mempty</a> :: <a href="SafePrelude.html#t:IO">IO</a> a <a href="#v:mempty" class="selflink">#</a></p><p class="src"><a href="#v:mappend">mappend</a> :: <a href="SafePrelude.html#t:IO">IO</a> a -> <a href="SafePrelude.html#t:IO">IO</a> a -> <a href="SafePrelude.html#t:IO">IO</a> a <a href="#v:mappend" class="selflink">#</a></p><p class="src"><a href="#v:mconcat">mconcat</a> :: [<a href="SafePrelude.html#t:IO">IO</a> a] -> <a href="SafePrelude.html#t:IO">IO</a> a <a href="#v:mconcat" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Monoid:Monoid:10" class="instance expander" onclick="toggleSection('i:ic:Monoid:Monoid:10')"></span> <a href="SafePrelude.html#t:Ord">Ord</a> a => <a href="SafePrelude.html#t:Monoid">Monoid</a> (Max a)</span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:Monoid:Monoid:10" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:mempty">mempty</a> :: Max a <a href="#v:mempty" class="selflink">#</a></p><p class="src"><a href="#v:mappend">mappend</a> :: Max a -> Max a -> Max a <a href="#v:mappend" class="selflink">#</a></p><p class="src"><a href="#v:mconcat">mconcat</a> :: [Max a] -> Max a <a href="#v:mconcat" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Monoid:Monoid:11" class="instance expander" onclick="toggleSection('i:ic:Monoid:Monoid:11')"></span> <a href="SafePrelude.html#t:Ord">Ord</a> a => <a href="SafePrelude.html#t:Monoid">Monoid</a> (Min a)</span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:Monoid:Monoid:11" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:mempty">mempty</a> :: Min a <a href="#v:mempty" class="selflink">#</a></p><p class="src"><a href="#v:mappend">mappend</a> :: Min a -> Min a -> Min a <a href="#v:mappend" class="selflink">#</a></p><p class="src"><a href="#v:mconcat">mconcat</a> :: [Min a] -> Min a <a href="#v:mconcat" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:Monoid:Monoid:12" class="instance expander" onclick="toggleSection('i:ic:Monoid:Monoid:12')"></span> <a href="SafePrelude.html#t:Monoid">Monoid</a> a => <a href="SafePrelude.html#t:Monoid">Monoid</a> (<a href="SafePrelude.html#t:Identity">Identity</a> a)</span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:Monoid:Monoid:12" class="inst-details hide"><div class="
|
||
|
|
floating-point number.</p></div><div class="subs minimal"><p class="caption">Minimal complete definition</p><p class="src"><a href="SafePrelude.html#v:floatRadix">floatRadix</a>, <a href="SafePrelude.html#v:floatDigits">floatDigits</a>, <a href="SafePrelude.html#v:floatRange">floatRange</a>, <a href="SafePrelude.html#v:decodeFloat">decodeFloat</a>, <a href="SafePrelude.html#v:encodeFloat">encodeFloat</a>, <a href="SafePrelude.html#v:isNaN">isNaN</a>, <a href="SafePrelude.html#v:isInfinite">isInfinite</a>, <a href="SafePrelude.html#v:isDenormalized">isDenormalized</a>, <a href="SafePrelude.html#v:isNegativeZero">isNegativeZero</a>, <a href="SafePrelude.html#v:isIEEE">isIEEE</a></p></div><div class="subs instances"><p id="control.i:RealFloat" class="caption collapser" onclick="toggleSection('i:RealFloat')">Instances</p><div id="section.i:RealFloat" class="show"><table><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:RealFloat:RealFloat:1" class="instance expander" onclick="toggleSection('i:ic:RealFloat:RealFloat:1')"></span> <a href="SafePrelude.html#t:RealFloat">RealFloat</a> <a href="SafePrelude.html#t:Double">Double</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:RealFloat:RealFloat:1" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:floatRadix">floatRadix</a> :: <a href="SafePrelude.html#t:Double">Double</a> -> <a href="SafePrelude.html#t:Integer">Integer</a> <a href="#v:floatRadix" class="selflink">#</a></p><p class="src"><a href="#v:floatDigits">floatDigits</a> :: <a href="SafePrelude.html#t:Double">Double</a> -> <a href="SafePrelude.html#t:Int">Int</a> <a href="#v:floatDigits" class="selflink">#</a></p><p class="src"><a href="#v:floatRange">floatRange</a> :: <a href="SafePrelude.html#t:Double">Double</a> -> (<a href="SafePrelude.html#t:Int">Int</a>, <a href="SafePrelude.html#t:Int">Int</a>) <a href="#v:floatRange" class="selflink">#</a></p><p class="src"><a href="#v:decodeFloat">decodeFloat</a> :: <a href="SafePrelude.html#t:Double">Double</a> -> (<a href="SafePrelude.html#t:Integer">Integer</a>, <a href="SafePrelude.html#t:Int">Int</a>) <a href="#v:decodeFloat" class="selflink">#</a></p><p class="src"><a href="#v:encodeFloat">encodeFloat</a> :: <a href="SafePrelude.html#t:Integer">Integer</a> -> <a href="SafePrelude.html#t:Int">Int</a> -> <a href="SafePrelude.html#t:Double">Double</a> <a href="#v:encodeFloat" class="selflink">#</a></p><p class="src"><a href="#v:exponent">exponent</a> :: <a href="SafePrelude.html#t:Double">Double</a> -> <a href="SafePrelude.html#t:Int">Int</a> <a href="#v:exponent" class="selflink">#</a></p><p class="src"><a href="#v:significand">significand</a> :: <a href="SafePrelude.html#t:Double">Double</a> -> <a href="SafePrelude.html#t:Double">Double</a> <a href="#v:significand" class="selflink">#</a></p><p class="src"><a href="#v:scaleFloat">scaleFloat</a> :: <a href="SafePrelude.html#t:Int">Int</a> -> <a href="SafePrelude.html#t:Double">Double</a> -> <a href="SafePrelude.html#t:Double">Double</a> <a href="#v:scaleFloat" class="selflink">#</a></p><p class="src"><a href="#v:isNaN">isNaN</a> :: <a href="SafePrelude.html#t:Double">Double</a> -> <a href="SafePrelude.html#t:Bool">Bool</a> <a href="#v:isNaN" class="selflink">#</a></p><p class="src"><a href="#v:isInfinite">isInfinite</a> :: <a href="SafePrelude.html#t:Double">Double</a> -> <a href="SafePrelude.html#t:Bool">Bool</a> <a href="#v:isInfinite" class="selflink">#</a></p><p class="src"><a href="#v:isDenormalized">isDenormalized</a> :: <a href="SafePrelude.html#t:Double">Double</a> -> <a href="SafePrelude.html#t:Bool">Bool</a> <a href="#v:isDenormalized" class="selflink">#</a></p><p class="src"><a href="#v:isNegativeZero">isNegativeZero</a> :: <a href="SafePrelude.html#t:Double">Double</a> -> <a href="SafePrelude.html#t:Bool">Bool</a> <a href="#v:isNegativeZero" class="selflink">#</a></p><p class="src"><a href="#v:isIEEE">isIEEE</a> :: <a href="SafePrelude.html#t:Do
|
||
|
|
application <code>(f x)</code> means the same as <code>(f <code><a href="SafePrelude.html#v:-36-">$</a></code> x)</code>. However, <code><a href="SafePrelude.html#v:-36-">$</a></code> has
|
||
|
|
low, right-associative binding precedence, so it sometimes allows
|
||
|
|
parentheses to be omitted; for example:</p><pre> f $ g $ h x = f (g (h x))</pre><p>It is also useful in higher-order situations, such as <code><code><a href="../base-4.9.0.0/GHC-OldList.html#v:map">map</a></code> (<code><a href="SafePrelude.html#v:-36-">$</a></code> 0) xs</code>,
|
||
|
|
or <code><code><a href="../base-4.9.0.0/Data-List.html#v:zipWith">zipWith</a></code> (<code><a href="SafePrelude.html#v:-36-">$</a></code>) fs xs</code>.</p></div></div><div class="top"><p class="src"><a id="v:-38-" class="def">(&)</a> :: a -> (a -> b) -> b <span class="fixity">infixl 1</span><span class="rightedge"></span> <a href="#v:-38-" class="selflink">#</a></p><div class="doc"><p><code><a href="SafePrelude.html#v:-38-">&</a></code> is a reverse application operator. This provides notational
|
||
|
|
convenience. Its precedence is one higher than that of the forward
|
||
|
|
application operator <code><a href="SafePrelude.html#v:-36-">$</a></code>, which allows <code><a href="SafePrelude.html#v:-38-">&</a></code> to be nested in <code><a href="SafePrelude.html#v:-36-">$</a></code>.</p><p><em>Since: 4.8.0.0</em></p></div></div><div class="top"><p class="src"><a id="v:-36--33-" class="def">($!)</a> :: (a -> b) -> a -> b <span class="fixity">infixr 0</span><span class="rightedge"></span> <a href="#v:-36--33-" class="selflink">#</a></p><div class="doc"><p>Strict (call-by-value) application operator. It takes a function and an
|
||
|
|
argument, evaluates the argument to weak head normal form (WHNF), then calls
|
||
|
|
the function with that value.</p></div></div><div class="top"><p class="src"><a id="v:-38--38-" class="def">(&&)</a> :: <a href="SafePrelude.html#t:Bool">Bool</a> -> <a href="SafePrelude.html#t:Bool">Bool</a> -> <a href="SafePrelude.html#t:Bool">Bool</a> <span class="fixity">infixr 3</span><span class="rightedge"></span> <a href="#v:-38--38-" class="selflink">#</a></p><div class="doc"><p>Boolean "and"</p></div></div><div class="top"><p class="src"><a id="v:-124--124-" class="def">(||)</a> :: <a href="SafePrelude.html#t:Bool">Bool</a> -> <a href="SafePrelude.html#t:Bool">Bool</a> -> <a href="SafePrelude.html#t:Bool">Bool</a> <span class="fixity">infixr 2</span><span class="rightedge"></span> <a href="#v:-124--124-" class="selflink">#</a></p><div class="doc"><p>Boolean "or"</p></div></div><div class="top"><p class="src"><a id="v:." class="def">(.)</a> :: (b -> c) -> (a -> b) -> a -> c <span class="fixity">infixr 9</span><span class="rightedge"></span> <a href="#v:." class="selflink">#</a></p><div class="doc"><p>Function composition.</p></div></div><div class="top"><p class="src"><a id="v:not" class="def">not</a> :: <a href="SafePrelude.html#t:Bool">Bool</a> -> <a href="SafePrelude.html#t:Bool">Bool</a> <a href="#v:not" class="selflink">#</a></p><div class="doc"><p>Boolean "not"</p></div></div><div class="top"><p class="src"><a id="v:otherwise" class="def">otherwise</a> :: <a href="SafePrelude.html#t:Bool">Bool</a> <a href="#v:otherwise" class="selflink">#</a></p><div class="doc"><p><code><a href="SafePrelude.html#v:otherwise">otherwise</a></code> is defined as the value <code><a href="SafePrelude.html#v:True">True</a></code>. It helps to make
|
||
|
|
guards more readable. eg.</p><pre> f x | x < 0 = ...
|
||
|
|
| otherwise = ...</pre></div></div><div class="top"><p class="src"><a id="v:fst" class="def">fst</a> :: (a, b) -> a <a href="#v:fst" class="selflink">#</a></p><div class="doc"><p>Extract the first component of a pair.</p></div></div><div class="top"><p class="src"><a id="v:snd" class="def">snd</a> :: (a, b) -> b <a href="#v:snd" class="selflink">#</a></p><div class="doc"><p>Extract the second component of a pair.</p></div></div><div class="top"><p class="src"><a id="v:id" class="def">id</a> :: a -> a <a href="#v:id" class="selflink">#</a></p><div class="doc"><p>Identity function.</p></div></div><div class="top"><p class="src"><a id="v:maybe" class="def">maybe</a> :: b -> (a -> b) -> <a href="SafePrelude.html#t:Maybe">Maybe</a> a -> b <a href="#v:maybe" class="selflink">#</a></p><div class="doc"><p>The <code><a href="SafePrelude.html#v:maybe">maybe</a></code> function takes a default value, a function, and a <code><a href="SafePrelude.html#t:Maybe">Maybe</a></code>
|
||
|
|
value. If the <code><a href="SafePrelude.html#t:Maybe">Maybe</a></code> value is <code><a href="SafePrelude.html#v:Nothing">Nothing</a></code>, the function returns the
|
||
|
|
default value. Otherwise, it applies the function to the value inside
|
||
|
|
the <code><a href="SafePrelude.html#v:Just">Just</a></code> and returns the result.</p><h4 id="control.ch:maybe0" class="caption expander" onclick="toggleSection('ch:maybe0')">Examples</h4><div id="section.ch:maybe0" class="hide"><p>Basic usage:</p><pre class="screen"><code class="prompt">>>> </code><strong class="userinput"><code>maybe False odd (Just 3)
|
||
|
|
</code></strong>True
|
||
|
|
</pre><pre class="screen"><code class="prompt">>>> </code><strong class="userinput"><code>maybe False odd Nothing
|
||
|
|
</code></strong>False
|
||
|
|
</pre><p>Read an integer from a string using <code>readMaybe</code>. If we succeed,
|
||
|
|
return twice the integer; that is, apply <code>(*2)</code> to it. If instead
|
||
|
|
we fail to parse an integer, return <code>0</code> by default:</p><pre class="screen"><code class="prompt">>>> </code><strong class="userinput"><code>import Text.Read ( readMaybe )
|
||
|
|
</code></strong><code class="prompt">>>> </code><strong class="userinput"><code>maybe 0 (*2) (readMaybe "5")
|
||
|
|
</code></strong>10
|
||
|
|
<code class="prompt">>>> </code><strong class="userinput"><code>maybe 0 (*2) (readMaybe "")
|
||
|
|
</code></strong>0
|
||
|
|
</pre><p>Apply <code>show</code> to a <code>Maybe Int</code>. If we have <code>Just n</code>, we want to show
|
||
|
|
the underlying <code><a href="SafePrelude.html#t:Int">Int</a></code> <code>n</code>. But if we have <code><a href="SafePrelude.html#v:Nothing">Nothing</a></code>, we return the
|
||
|
|
empty string instead of (for example) "Nothing":</p><pre class="screen"><code class="prompt">>>> </code><strong class="userinput"><code>maybe "" show (Just 5)
|
||
|
|
</code></strong>"5"
|
||
|
|
<code class="prompt">>>> </code><strong class="userinput"><code>maybe "" show Nothing
|
||
|
|
</code></strong>""
|
||
|
|
</pre></div></div></div><div class="top"><p class="src"><a id="v:either" class="def">either</a> :: (a -> c) -> (b -> c) -> <a href="SafePrelude.html#t:Either">Either</a> a b -> c <a href="#v:either" class="selflink">#</a></p><div class="doc"><p>Case analysis for the <code><a href="SafePrelude.html#t:Either">Either</a></code> type.
|
||
|
|
If the value is <code><code><a href="SafePrelude.html#v:Left">Left</a></code> a</code>, apply the first function to <code>a</code>;
|
||
|
|
if it is <code><code><a href="SafePrelude.html#v:Right">Right</a></code> b</code>, apply the second function to <code>b</code>.</p><h4 id="control.ch:either0" class="caption expander" onclick="toggleSection('ch:either0')">Examples</h4><div id="section.ch:either0" class="hide"><p>We create two values of type <code><code><a href="SafePrelude.html#t:Either">Either</a></code> <code><a href="SafePrelude.html#t:String">String</a></code> <code><a href="SafePrelude.html#t:Int">Int</a></code></code>, one using the
|
||
|
|
<code><a href="SafePrelude.html#v:Left">Left</a></code> constructor and another using the <code><a href="SafePrelude.html#v:Right">Right</a></code> constructor. Then
|
||
|
|
we apply "either" the <code>length</code> function (if we have a <code><a href="SafePrelude.html#t:String">String</a></code>)
|
||
|
|
or the "times-two" function (if we have an <code><a href="SafePrelude.html#t:Int">Int</a></code>):</p><pre class="screen"><code class="prompt">>>> </code><strong class="userinput"><code>let s = Left "foo" :: Either String Int
|
||
|
|
</code></strong><code class="prompt">>>> </code><strong class="userinput"><code>let n = Right 3 :: Either String Int
|
||
|
|
</code></strong><code class="prompt">>>> </code><strong class="userinput"><code>either length (*2) s
|
||
|
|
</code></strong>3
|
||
|
|
<code class="prompt">>>> </code><strong class="userinput"><code>either length (*2) n
|
||
|
|
</code></strong>6
|
||
|
|
</pre></div></div></div><div class="top"><p class="src"><a id="v:flip" class="def">flip</a> :: (a -> b -> c) -> b -> a -> c <a href="#v:flip" class="selflink">#</a></p><div class="doc"><p><code><code><a href="SafePrelude.html#v:flip">flip</a></code> f</code> takes its (first) two arguments in the reverse order of <code>f</code>.</p></div></div><div class="top"><p class="src"><a id="v:const" class="def">const</a> :: a -> b -> a <a href="#v:const" class="selflink">#</a></p><div class="doc"><p><code>const x</code> is a unary function which evaluates to <code>x</code> for all inputs.</p><p>For instance,</p><pre class="screen"><code class="prompt">>>> </code><strong class="userinput"><code>map (const 42) [0..3]
|
||
|
|
</code></strong>[42,42,42,42]
|
||
|
|
</pre></div></div><div class="top"><p class="src"><a id="v:odd" class="def">odd</a> :: <a href="SafePrelude.html#t:Integral">Integral</a> a => a -> <a href="SafePrelude.html#t:Bool">Bool</a> <a href="#v:odd" class="selflink">#</a></p></div><div class="top"><p class="src"><a id="v:even" class="def">even</a> :: <a href="SafePrelude.html#t:Integral">Integral</a> a => a -> <a href="SafePrelude.html#t:Bool">Bool</a> <a href="#v:even" class="selflink">#</a></p></div><div class="top"><p class="src"><a id="v:uncurry" class="def">uncurry</a> :: (a -> b -> c) -> (a, b) -> c <a href="#v:uncurry" class="selflink">#</a></p><div class="doc"><p><code><a href="SafePrelude.html#v:uncurry">uncurry</a></code> converts a curried function to a function on pairs.</p></div></div><div class="top"><p class="src"><a id="v:curry" class="def">curry</a> :: ((a, b) -> c) -> a -> b -> c <a href="#v:curry" class="selflink">#</a></p><div class="doc"><p><code><a href="SafePrelude.html#v:curry">curry</a></code> converts an uncurried function to a curried function.</p></div></div><div class="top"><p class="src"><a id="v:asTypeOf" class="def">asTypeOf</a> :: a -> a -> a <a href="#v:asTypeOf" class="selflink">#</a></p><div class="doc"><p><code><a href="SafePrelude.html#v:asTypeOf">asTypeOf</a></code> is a type-restricted version of <code><a href="SafePrelude.html#v:const">const</a></code>. It is usually
|
||
|
|
used as an infix operator, and its typing forces its first argument
|
||
|
|
(which is usually overloaded) to have the same type as the second.</p></div></div><div class="top"><p class="src"><a id="v:seq" class="def">seq</a> :: a -> b -> b <a href="#v:seq" class="selflink">#</a></p><div class="doc"><p>The value of <code>seq a b</code> is bottom if <code>a</code> is bottom, and
|
||
|
|
otherwise equal to <code>b</code>. <code>seq</code> is usually introduced to
|
||
|
|
improve performance by avoiding unneeded laziness.</p><p>A note on evaluation order: the expression <code>seq a b</code> does
|
||
|
|
<em>not</em> guarantee that <code>a</code> will be evaluated before <code>b</code>.
|
||
|
|
The only guarantee given by <code>seq</code> is that the both <code>a</code>
|
||
|
|
and <code>b</code> will be evaluated before <code>seq</code> returns a value.
|
||
|
|
In particular, this means that <code>b</code> may be evaluated before
|
||
|
|
<code>a</code>. If you need to guarantee a specific order of evaluation,
|
||
|
|
you must use the function <code>pseq</code> from the "parallel" package. </p></div></div><div class="top"><p class="src"><a id="v:fix" class="def">fix</a> :: (a -> a) -> a <a href="#v:fix" class="selflink">#</a></p><div class="doc"><p><code><code><a href="SafePrelude.html#v:fix">fix</a></code> f</code> is the least fixed point of the function <code>f</code>,
|
||
|
|
i.e. the least defined <code>x</code> such that <code>f x = x</code>.</p></div></div><h2 id="g:6">Numeric</h2><div class="top"><p class="src"><a id="v:-94-" class="def">(^)</a> :: (<a href="SafePrelude.html#t:Num">Num</a> a, <a href="SafePrelude.html#t:Integral">Integral</a> b) => a -> b -> a <span class="fixity">infixr 8</span><span class="rightedge"></span> <a href="#v:-94-" class="selflink">#</a></p><div class="doc"><p>raise a number to a non-negative integral power</p></div></div><div class="top"><p class="src"><a id="v:-94--94-" class="def">(^^)</a> :: (<a href="SafePrelude.html#t:Fractional">Fractional</a> a, <a href="SafePrelude.html#t:Integral">Integral</a> b) => a -> b -> a <span class="fixity">infixr 8</span><span class="rightedge"></span> <a href="#v:-94--94-" class="selflink">#</a></p><div class="doc"><p>raise a number to an integral power</p></div></div><div class="top"><p class="src"><a id="v:subtract" class="def">subtract</a> :: <a href="SafePrelude.html#t:Num">Num</a> a => a -> a -> a <a href="#v:subtract" class="selflink">#</a></p><div class="doc"><p>the same as <code><code><a href="SafePrelude.html#v:flip">flip</a></code> (<code><a href="SafePrelude.html#v:-45-">-</a></code>)</code>.</p><p>Because <code>-</code> is treated specially in the Haskell grammar,
|
||
|
|
<code>(-</code> <em>e</em><code>)</code> is not a section, but an application of prefix negation.
|
||
|
|
However, <code>(<code><a href="SafePrelude.html#v:subtract">subtract</a></code></code> <em>exp</em><code>)</code> is equivalent to the disallowed section.</p></div></div><div class="top"><p class="src"><a id="v:fromIntegral" class="def">fromIntegral</a> :: (<a href="SafePrelude.html#t:Integral">Integral</a> a, <a href="SafePrelude.html#t:Num">Num</a> b) => a -> b <a href="#v:fromIntegral" class="selflink">#</a></p><div class="doc"><p>general coercion from integral types</p></div></div><div class="top"><p class="src"><a id="v:realToFrac" class="def">realToFrac</a> :: (<a href="SafePrelude.html#t:Real">Real</a> a, <a href="SafePrelude.html#t:Fractional">Fractional</a> b) => a -> b <a href="#v:realToFrac" class="selflink">#</a></p><div class="doc"><p>general coercion to fractional types</p></div></div><h2 id="g:7">Foldable</h2><div class="top"><p class="src"><a id="v:sum" class="def">sum</a> :: (<a href="SafePrelude.html#t:Foldable">Foldable</a> f, <a href="SafePrelude.html#t:Num">Num</a> a) => f a -> a <a href="src/SafePrelude.html#sum" class="link">Source</a> <a href="#v:sum" class="selflink">#</a></p><div class="doc"><p>Get the sum of the elements in a <code><a href="SafePrelude.html#t:Foldable">Foldable</a></code>.</p><p>This is not the same as the function from <code><a href="Data.html#v:Foldable">Foldable</a></code>; instead,
|
||
|
|
this function uses a strict left fold.</p><p><em>Since: 0.1.0.0</em></p></div></div><div class="top"><p class="src"><a id="v:product" class="def">product</a> :: (<a href="SafePrelude.html#t:Foldable">Foldable</a> f, <a href="SafePrelude.html#t:Num">Num</a> a) => f a -> a <a href="src/SafePrelude.html#product" class="link">Source</a> <a href="#v:product" class="selflink">#</a></p><div class="doc"><p>Get the product of the elements in a <code><a href="SafePrelude.html#t:Foldable">Foldable</a></code>.</p><p>This is not the same as the function from <code><a href="Data.html#v:Foldable">Foldable</a></code>; instead,
|
||
|
|
this function uses a strict left fold.</p><p><em>Since: 0.1.0.0</em></p></div></div><div class="top"><p class="src"><a id="v:foldrM" class="def">foldrM</a> :: (<a href="SafePrelude.html#t:Foldable">Foldable</a> t, <a href="SafePrelude.html#t:Monad">Monad</a> m) => (a -> b -> m b) -> b -> t a -> m b <a href="#v:foldrM" class="selflink">#</a></p><div class="doc"><p>Monadic fold over the elements of a structure,
|
||
|
|
associating to the right, i.e. from right to left.</p></div></div><div class="top"><p class="src"><a id="v:foldlM" class="def">foldlM</a> :: (<a href="SafePrelude.html#t:Foldable">Foldable</a> t, <a href="SafePrelude.html#t:Monad">Monad</a> m) => (b -> a -> m b) -> b -> t a -> m b <a href="#v:foldlM" class="selflink">#</a></p><div class="doc"><p>Monadic fold over the elements of a structure,
|
||
|
|
associating to the left, i.e. from left to right.</p></div></div><div class="top"><p class="src"><a id="v:traverse_" class="def">traverse_</a> :: (<a href="SafePrelude.html#t:Foldable">Foldable</a> t, <a href="SafePrelude.html#t:Applicative">Applicative</a> f) => (a -> f b) -> t a -> f () <a href="#v:traverse_" class="selflink">#</a></p><div class="doc"><p>Map each element of a structure to an action, evaluate these
|
||
|
|
actions from left to right, and ignore the results. For a version
|
||
|
|
that doesn't ignore the results see <code><a href="../base-4.9.0.0/Data-Traversable.html#v:traverse">traverse</a></code>.</p></div></div><div class="top"><p class="src"><a id="v:for_" class="def">for_</a> :: (<a href="SafePrelude.html#t:Foldable">Foldable</a> t, <a href="SafePrelude.html#t:Applicative">Applicative</a> f) => t a -> (a -> f b) -> f () <a href="#v:for_" class="selflink">#</a></p><div class="doc"><p><code><a href="SafePrelude.html#v:for_">for_</a></code> is <code><a href="SafePrelude.html#v:traverse_">traverse_</a></code> with its arguments flipped. For a version
|
||
|
|
that doesn't ignore the results see <code><a href="../base-4.9.0.0/Data-Traversable.html#v:for">for</a></code>.</p><pre class="screen"><code class="prompt">>>> </code><strong class="userinput"><code>for_ [1..4] print
|
||
|
|
</code></strong>1
|
||
|
|
2
|
||
|
|
3
|
||
|
|
4
|
||
|
|
</pre></div></div><div class="top"><p class="src"><a id="v:sequenceA_" class="def">sequenceA_</a> :: (<a href="SafePrelude.html#t:Foldable">Foldable</a> t, <a href="SafePrelude.html#t:Applicative">Applicative</a> f) => t (f a) -> f () <a href="#v:sequenceA_" class="selflink">#</a></p><div class="doc"><p>Evaluate each action in the structure from left to right, and
|
||
|
|
ignore the results. For a version that doesn't ignore the results
|
||
|
|
see <code><a href="../base-4.9.0.0/Data-Traversable.html#v:sequenceA">sequenceA</a></code>.</p></div></div><div class="top"><p class="src"><a id="v:asum" class="def">asum</a> :: (<a href="SafePrelude.html#t:Foldable">Foldable</a> t, <a href="SafePrelude.html#t:Alternative">Alternative</a> f) => t (f a) -> f a <a href="#v:asum" class="selflink">#</a></p><div class="doc"><p>The sum of a collection of actions, generalizing <code><a href="SafePrelude.html#v:concat">concat</a></code>.</p></div></div><div class="top"><p class="src"><a id="v:mapM_" class="def">mapM_</a> :: (<a href="SafePrelude.html#t:Applicative">Applicative</a> m, <a href="SafePrelude.html#t:Foldable">Foldable</a> f) => (a -> m b) -> f a -> m () <a href="src/SafePrelude.html#mapM_" class="link">Source</a> <a href="#v:mapM_" class="selflink">#</a></p><div class="doc"><p>Synonym for <code><a href="SafePrelude.html#v:traverse_">traverse_</a></code>; different from base to generalize to
|
||
|
|
<code><a href="SafePrelude.html#t:Applicative">Applicative</a></code>.</p><p><em>Since: 0.1.0.0</em></p></div></div><div class="top"><p class="src"><a id="v:forM_" class="def">forM_</a> :: (<a href="SafePrelude.html#t:Applicative">Applicative</a> m, <a href="SafePrelude.html#t:Foldable">Foldable</a> f) => f a -> (a -> m b) -> m () <a href="src/SafePrelude.html#forM_" class="link">Source</a> <a href="#v:forM_" class="selflink">#</a></p><div class="doc"><p>Flipped version of <code><a href="SafePrelude.html#v:mapM_">mapM_</a></code>.</p><p><em>Since: 0.1.0.0</em></p></div></div><div class="top"><p class="src"><a id="v:sequence_" class="def">sequence_</a> :: (<a href="SafePrelude.html#t:Applicative">Applicative</a> m, <a href="SafePrelude.html#t:Foldable">Foldable</a> f) => f (m a) -> m () <a href="src/SafePrelude.html#sequence_" class="link">Source</a> <a href="#v:sequence_" class="selflink">#</a></p><div class="doc"><p>Synonym for <code><a href="SafePrelude.html#v:sequence_">sequence_</a></code>; different from base to generalize to
|
||
|
|
<code><a href="SafePrelude.html#t:Applicative">Applicative</a></code>.</p><p><em>Since: 0.1.0.0</em></p></div></div><div class="top"><p class="src"><a id="v:msum" class="def">msum</a> :: (<a href="SafePrelude.html#t:Foldable">Foldable</a> t, <a href="../base-4.9.0.0/Control-Monad.html#t:MonadPlus">MonadPlus</a> m) => t (m a) -> m a <a href="#v:msum" class="selflink">#</a></p><div class="doc"><p>The sum of a collection of actions, generalizing <code><a href="SafePrelude.html#v:concat">concat</a></code>.
|
||
|
|
As of base 4.8.0.0, <code><a href="SafePrelude.html#v:msum">msum</a></code> is just <code><a href="SafePrelude.html#v:asum">asum</a></code>, specialized to <code><a href="../base-4.9.0.0/Control-Monad.html#t:MonadPlus">MonadPlus</a></code>.</p></div></div><div class="top"><p class="src"><a id="v:concat" class="def">concat</a> :: <a href="SafePrelude.html#t:Foldable">Foldable</a> t => t [a] -> [a] <a href="#v:concat" class="selflink">#</a></p><div class="doc"><p>The concatenation of all the elements of a container of lists.</p></div></div><div class="top"><p class="src"><a id="v:concatMap" class="def">concatMap</a> :: <a href="SafePrelude.html#t:Foldable">Foldable</a> t => (a -> [b]) -> t a -> [b] <a href="#v:concatMap" class="selflink">#</a></p><div class="doc"><p>Map a function over all the elements of a container and concatenate
|
||
|
|
the resulting lists.</p></div></div><div class="top"><p class="src"><a id="v:and" class="def">and</a> :: <a href="SafePrelude.html#t:Foldable">Foldable</a> t => t <a href="SafePrelude.html#t:Bool">Bool</a> -> <a href="SafePrelude.html#t:Bool">Bool</a> <a href="#v:and" class="selflink">#</a></p><div class="doc"><p><code><a href="SafePrelude.html#v:and">and</a></code> returns the conjunction of a container of Bools. For the
|
||
|
|
result to be <code><a href="SafePrelude.html#v:True">True</a></code>, the container must be finite; <code><a href="SafePrelude.html#v:False">False</a></code>, however,
|
||
|
|
results from a <code><a href="SafePrelude.html#v:False">False</a></code> value finitely far from the left end.</p></div></div><div class="top"><p class="src"><a id="v:or" class="def">or</a> :: <a href="SafePrelude.html#t:Foldable">Foldable</a> t => t <a href="SafePrelude.html#t:Bool">Bool</a> -> <a href="SafePrelude.html#t:Bool">Bool</a> <a href="#v:or" class="selflink">#</a></p><div class="doc"><p><code><a href="SafePrelude.html#v:or">or</a></code> returns the disjunction of a container of Bools. For the
|
||
|
|
result to be <code><a href="SafePrelude.html#v:False">False</a></code>, the container must be finite; <code><a href="SafePrelude.html#v:True">True</a></code>, however,
|
||
|
|
results from a <code><a href="SafePrelude.html#v:True">True</a></code> value finitely far from the left end.</p></div></div><div class="top"><p class="src"><a id="v:any" class="def">any</a> :: <a href="SafePrelude.html#t:Foldable">Foldable</a> t => (a -> <a href="SafePrelude.html#t:Bool">Bool</a>) -> t a -> <a href="SafePrelude.html#t:Bool">Bool</a> <a href="#v:any" class="selflink">#</a></p><div class="doc"><p>Determines whether any element of the structure satisfies the predicate.</p></div></div><div class="top"><p class="src"><a id="v:all" class="def">all</a> :: <a href="SafePrelude.html#t:Foldable">Foldable</a> t => (a -> <a href="SafePrelude.html#t:Bool">Bool</a>) -> t a -> <a href="SafePrelude.html#t:Bool">Bool</a> <a href="#v:all" class="selflink">#</a></p><div class="doc"><p>Determines whether all elements of the structure satisfy the predicate.</p></div></div><div class="top"><p class="src"><a id="v:notElem" class="def">notElem</a> :: (<a href="SafePrelude.html#t:Foldable">Foldable</a> t, <a href="SafePrelude.html#t:Eq">Eq</a> a) => a -> t a -> <a href="SafePrelude.html#t:Bool">Bool</a> <span class="fixity">infix 4</span><span class="rightedge"></span> <a href="#v:notElem" class="selflink">#</a></p><div class="doc"><p><code><a href="SafePrelude.html#v:notElem">notElem</a></code> is the negation of <code><a href="SafePrelude.html#v:elem">elem</a></code>.</p></div></div><div class="top"><p class="src"><a id="v:find" class="def">find</a> :: <a href="SafePrelude.html#t:Foldable">Foldable</a> t => (a -> <a href="SafePrelude.html#t:Bool">Bool</a>) -> t a -> <a href="SafePrelude.html#t:Maybe">Maybe</a> a <a href="#v:find" class="selflink">#</a></p><div class="doc"><p>The <code><a href="SafePrelude.html#v:find">find</a></code> function takes a predicate and a structure and returns
|
||
|
|
the leftmost element of the structure matching the predicate, or
|
||
|
|
<code><a href="SafePrelude.html#v:Nothing">Nothing</a></code> if there is no such element.</p></div></div><h2 id="g:8">Traversable</h2><div class="top"><p class="src"><a id="v:mapM" class="def">mapM</a> :: (<a href="SafePrelude.html#t:Applicative">Applicative</a> m, <a href="SafePrelude.html#t:Traversable">Traversable</a> t) => (a -> m b) -> t a -> m (t b) <a href="src/SafePrelude.html#mapM" class="link">Source</a> <a href="#v:mapM" class="selflink">#</a></p><div class="doc"><p>Synonym for <code><a href="SafePrelude.html#v:traverse">traverse</a></code>; different from base to generalize to
|
||
|
|
<code><a href="SafePrelude.html#t:Applicative">Applicative</a></code>.</p><p><em>Since: 0.1.0.0</em></p></div></div><div class="top"><p class="src"><a id="v:sequence" class="def">sequence</a> :: (<a href="SafePrelude.html#t:Applicative">Applicative</a> m, <a href="SafePrelude.html#t:Traversable">Traversable</a> t) => t (m a) -> m (t a) <a href="src/SafePrelude.html#sequence" class="link">Source</a> <a href="#v:sequence" class="selflink">#</a></p><div class="doc"><p>Synonym for <code><a href="SafePrelude.html#v:sequenceA">sequenceA</a></code>; different from base to generalize to
|
||
|
|
<code><a href="SafePrelude.html#t:Applicative">Applicative</a></code>.</p><p><em>Since: 0.1.0.0</em></p></div></div><div class="top"><p class="src"><a id="v:for" class="def">for</a> :: (<a href="SafePrelude.html#t:Traversable">Traversable</a> t, <a href="SafePrelude.html#t:Applicative">Applicative</a> f) => t a -> (a -> f b) -> f (t b) <a href="#v:for" class="selflink">#</a></p><div class="doc"><p><code><a href="SafePrelude.html#v:for">for</a></code> is <code><a href="SafePrelude.html#v:traverse">traverse</a></code> with its arguments flipped. For a version
|
||
|
|
that ignores the results see <code><a href="../base-4.9.0.0/Data-Foldable.html#v:for_">for_</a></code>.</p></div></div><div class="top"><p class="src"><a id="v:forM" class="def">forM</a> :: (<a href="SafePrelude.html#t:Applicative">Applicative</a> m, <a href="SafePrelude.html#t:Traversable">Traversable</a> t) => t a -> (a -> m b) -> m (t b) <a href="src/SafePrelude.html#forM" class="link">Source</a> <a href="#v:forM" class="selflink">#</a></p><div class="doc"><p>Flipped version of <code><a href="SafePrelude.html#v:mapM">mapM</a></code>.</p><p><em>Since: 0.1.0.0</em></p></div></div><div class="top"><p class="src"><a id="v:mapAccumL" class="def">mapAccumL</a> :: <a href="SafePrelude.html#t:Traversable">Traversable</a> t => (a -> b -> (a, c)) -> a -> t b -> (a, t c) <a href="#v:mapAccumL" class="selflink">#</a></p><div class="doc"><p>The <code><a href="SafePrelude.html#v:mapAccumL">mapAccumL</a></code> function behaves like a combination of <code><a href="SafePrelude.html#v:fmap">fmap</a></code>
|
||
|
|
and <code>foldl</code>; it applies a function to each element of a structure,
|
||
|
|
passing an accumulating parameter from left to right, and returning
|
||
|
|
a final value of this accumulator together with the new structure.</p></div></div><div class="top"><p class="src"><a id="v:mapAccumR" class="def">mapAccumR</a> :: <a href="SafePrelude.html#t:Traversable">Traversable</a> t => (a -> b -> (a, c)) -> a -> t b -> (a, t c) <a href="#v:mapAccumR" class="selflink">#</a></p><div class="doc"><p>The <code><a href="SafePrelude.html#v:mapAccumR">mapAccumR</a></code> function behaves like a combination of <code><a href="SafePrelude.html#v:fmap">fmap</a></code>
|
||
|
|
and <code>foldr</code>; it applies a function to each element of a structure,
|
||
|
|
passing an accumulating parameter from right to left, and returning
|
||
|
|
a final value of this accumulator together with the new structure.</p></div></div><h2 id="g:9">Functor</h2><div class="top"><p class="src"><a id="v:-36--62-" class="def">($>)</a> :: <a href="SafePrelude.html#t:Functor">Functor</a> f => f a -> b -> f b <span class="fixity">infixl 4</span><span class="rightedge"></span> <a href="#v:-36--62-" class="selflink">#</a></p><div class="doc"><p>Flipped version of <code><a href="SafePrelude.html#v:-60--36-"><$</a></code>.</p><h4 id="control.ch:-36--62-0" class="caption expander" onclick="toggleSection('ch:-36--62-0')">Examples</h4><div id="section.ch:-36--62-0" class="hide"><p>Replace the contents of a <code><code>Maybe</code> <code>Int</code></code> with a constant <code>String</code>:</p><pre class="screen"><code class="prompt">>>> </code><strong class="userinput"><code>Nothing $> "foo"
|
||
|
|
</code></strong>Nothing
|
||
|
|
<code class="prompt">>>> </code><strong class="userinput"><code>Just 90210 $> "foo"
|
||
|
|
</code></strong>Just "foo"
|
||
|
|
</pre><p>Replace the contents of an <code><code>Either</code> <code>Int</code> <code>Int</code></code> with a constant
|
||
|
|
<code>String</code>, resulting in an <code><code>Either</code> <code>Int</code> <code>String</code></code>:</p><pre class="screen"><code class="prompt">>>> </code><strong class="userinput"><code>Left 8675309 $> "foo"
|
||
|
|
</code></strong>Left 8675309
|
||
|
|
<code class="prompt">>>> </code><strong class="userinput"><code>Right 8675309 $> "foo"
|
||
|
|
</code></strong>Right "foo"
|
||
|
|
</pre><p>Replace each element of a list with a constant <code>String</code>:</p><pre class="screen"><code class="prompt">>>> </code><strong class="userinput"><code>[1,2,3] $> "foo"
|
||
|
|
</code></strong>["foo","foo","foo"]
|
||
|
|
</pre><p>Replace the second element of a pair with a constant <code>String</code>:</p><pre class="screen"><code class="prompt">>>> </code><strong class="userinput"><code>(1,2) $> "foo"
|
||
|
|
</code></strong>(1,"foo")
|
||
|
|
</pre></div><p><em>Since: 4.7.0.0</em></p></div></div><div class="top"><p class="src"><a id="v:-60--36--62-" class="def">(<$>)</a> :: <a href="SafePrelude.html#t:Functor">Functor</a> f => (a -> b) -> f a -> f b <span class="fixity">infixl 4</span><span class="rightedge"></span> <a href="#v:-60--36--62-" class="selflink">#</a></p><div class="doc"><p>An infix synonym for <code><a href="SafePrelude.html#v:fmap">fmap</a></code>.</p><p>The name of this operator is an allusion to <code>$</code>.
|
||
|
|
Note the similarities between their types:</p><pre> ($) :: (a -> b) -> a -> b
|
||
|
|
(<$>) :: Functor f => (a -> b) -> f a -> f b</pre><p>Whereas <code>$</code> is function application, <code><a href="SafePrelude.html#v:-60--36--62-"><$></a></code> is function
|
||
|
|
application lifted over a <code><a href="SafePrelude.html#t:Functor">Functor</a></code>.</p><h4 id="control.ch:-60--36--62-0" class="caption expander" onclick="toggleSection('ch:-60--36--62-0')">Examples</h4><div id="section.ch:-60--36--62-0" class="hide"><p>Convert from a <code><code>Maybe</code> <code>Int</code></code> to a <code><code>Maybe</code> <code>String</code></code> using <code>show</code>:</p><pre class="screen"><code class="prompt">>>> </code><strong class="userinput"><code>show <$> Nothing
|
||
|
|
</code></strong>Nothing
|
||
|
|
<code class="prompt">>>> </code><strong class="userinput"><code>show <$> Just 3
|
||
|
|
</code></strong>Just "3"
|
||
|
|
</pre><p>Convert from an <code><code>Either</code> <code>Int</code> <code>Int</code></code> to an <code><code>Either</code> <code>Int</code></code>
|
||
|
|
<code>String</code> using <code>show</code>:</p><pre class="screen"><code class="prompt">>>> </code><strong class="userinput"><code>show <$> Left 17
|
||
|
|
</code></strong>Left 17
|
||
|
|
<code class="prompt">>>> </code><strong class="userinput"><code>show <$> Right 17
|
||
|
|
</code></strong>Right "17"
|
||
|
|
</pre><p>Double each element of a list:</p><pre class="screen"><code class="prompt">>>> </code><strong class="userinput"><code>(*2) <$> [1,2,3]
|
||
|
|
</code></strong>[2,4,6]
|
||
|
|
</pre><p>Apply <code>even</code> to the second element of a pair:</p><pre class="screen"><code class="prompt">>>> </code><strong class="userinput"><code>even <$> (2,2)
|
||
|
|
</code></strong>(2,True)
|
||
|
|
</pre></div></div></div><div class="top"><p class="src"><a id="v:void" class="def">void</a> :: <a href="SafePrelude.html#t:Functor">Functor</a> f => f a -> f () <a href="#v:void" class="selflink">#</a></p><div class="doc"><p><code><code><a href="SafePrelude.html#v:void">void</a></code> value</code> discards or ignores the result of evaluation, such
|
||
|
|
as the return value of an <code><a href="../base-4.9.0.0/System-IO.html#v:IO">IO</a></code> action.</p><h4 id="control.ch:void0" class="caption expander" onclick="toggleSection('ch:void0')">Examples</h4><div id="section.ch:void0" class="hide"><p>Replace the contents of a <code><code>Maybe</code> <code>Int</code></code> with unit:</p><pre class="screen"><code class="prompt">>>> </code><strong class="userinput"><code>void Nothing
|
||
|
|
</code></strong>Nothing
|
||
|
|
<code class="prompt">>>> </code><strong class="userinput"><code>void (Just 3)
|
||
|
|
</code></strong>Just ()
|
||
|
|
</pre><p>Replace the contents of an <code><code>Either</code> <code>Int</code> <code>Int</code></code> with unit,
|
||
|
|
resulting in an <code><code>Either</code> <code>Int</code> '()'</code>:</p><pre class="screen"><code class="prompt">>>> </code><strong class="userinput"><code>void (Left 8675309)
|
||
|
|
</code></strong>Left 8675309
|
||
|
|
<code class="prompt">>>> </code><strong class="userinput"><code>void (Right 8675309)
|
||
|
|
</code></strong>Right ()
|
||
|
|
</pre><p>Replace every element of a list with unit:</p><pre class="screen"><code class="prompt">>>> </code><strong class="userinput"><code>void [1,2,3]
|
||
|
|
</code></strong>[(),(),()]
|
||
|
|
</pre><p>Replace the second element of a pair with unit:</p><pre class="screen"><code class="prompt">>>> </code><strong class="userinput"><code>void (1,2)
|
||
|
|
</code></strong>(1,())
|
||
|
|
</pre><p>Discard the result of an <code><a href="../base-4.9.0.0/System-IO.html#v:IO">IO</a></code> action:</p><pre class="screen"><code class="prompt">>>> </code><strong class="userinput"><code>mapM print [1,2]
|
||
|
|
</code></strong>1
|
||
|
|
2
|
||
|
|
[(),()]
|
||
|
|
<code class="prompt">>>> </code><strong class="userinput"><code>void $ mapM print [1,2]
|
||
|
|
</code></strong>1
|
||
|
|
2
|
||
|
|
</pre></div></div></div><h2 id="g:10">Applicative</h2><div class="top"><p class="src"><a id="v:liftA" class="def">liftA</a> :: <a href="SafePrelude.html#t:Applicative">Applicative</a> f => (a -> b) -> f a -> f b <a href="#v:liftA" class="selflink">#</a></p><div class="doc"><p>Lift a function to actions.
|
||
|
|
This function may be used as a value for <code><a href="SafePrelude.html#v:fmap">fmap</a></code> in a <code><a href="SafePrelude.html#t:Functor">Functor</a></code> instance.</p></div></div><div class="top"><p class="src"><a id="v:liftA2" class="def">liftA2</a> :: <a href="SafePrelude.html#t:Applicative">Applicative</a> f => (a -> b -> c) -> f a -> f b -> f c <a href="#v:liftA2" class="selflink">#</a></p><div class="doc"><p>Lift a binary function to actions.</p></div></div><div class="top"><p class="src"><a id="v:liftA3" class="def">liftA3</a> :: <a href="SafePrelude.html#t:Applicative">Applicative</a> f => (a -> b -> c -> d) -> f a -> f b -> f c -> f d <a href="#v:liftA3" class="selflink">#</a></p><div class="doc"><p>Lift a ternary function to actions.</p></div></div><h2 id="g:11">Alternative</h2><div class="top"><p class="src"><a id="v:optional" class="def">optional</a> :: <a href="SafePrelude.html#t:Alternative">Alternative</a> f => f a -> f (<a href="SafePrelude.html#t:Maybe">Maybe</a> a) <a href="#v:optional" class="selflink">#</a></p><div class="doc"><p>One or none.</p></div></div><h2 id="g:12">Monad</h2><div class="top"><p class="src"><a id="v:-61--60--60-" class="def">(=<<)</a> :: <a href="SafePrelude.html#t:Monad">Monad</a> m => (a -> m b) -> m a -> m b <span class="fixity">infixr 1</span><span class="rightedge"></span> <a href="#v:-61--60--60-" class="selflink">#</a></p><div class="doc"><p>Same as <code><a href="SafePrelude.html#v:-62--62--61-">>>=</a></code>, but with the arguments interchanged.</p></div></div><div class="top"><p class="src"><a id="v:-62--61--62-" class="def">(>=>)</a> :: <a href="SafePrelude.html#t:Monad">Monad</a> m => (a -> m b) -> (b -> m c) -> a -> m c <span class="fixity">infixr 1</span><span class="rightedge"></span> <a href="#v:-62--61--62-" class="selflink">#</a></p><div class="doc"><p>Left-to-right Kleisli composition of monads.</p></div></div><div class="top"><p class="src"><a id="v:-60--61--60-" class="def">(<=<)</a> :: <a href="SafePrelude.html#t:Monad">Monad</a> m => (b -> m c) -> (a -> m b) -> a -> m c <span class="fixity">infixr 1</span><span class="rightedge"></span> <a href="#v:-60--61--60-" class="selflink">#</a></p><div class="doc"><p>Right-to-left Kleisli composition of monads. <code>(<code><a href="SafePrelude.html#v:-62--61--62-">>=></a></code>)</code>, with the arguments flipped.</p><p>Note how this operator resembles function composition <code>(<code><a href="SafePrelude.html#v:.">.</a></code>)</code>:</p><pre>(.) :: (b -> c) -> (a -> b) -> a -> c
|
||
|
|
(<=<) :: Monad m => (b -> m c) -> (a -> m b) -> a -> m c</pre></div></div><div class="top"><p class="src"><a id="v:forever" class="def">forever</a> :: <a href="SafePrelude.html#t:Applicative">Applicative</a> f => f a -> f b <a href="#v:forever" class="selflink">#</a></p><div class="doc"><p><code><code><a href="SafePrelude.html#v:forever">forever</a></code> act</code> repeats the action infinitely.</p></div></div><div class="top"><p class="src"><a id="v:join" class="def">join</a> :: <a href="SafePrelude.html#t:Monad">Monad</a> m => m (m a) -> m a <a href="#v:join" class="selflink">#</a></p><div class="doc"><p>The <code><a href="SafePrelude.html#v:join">join</a></code> function is the conventional monad join operator. It
|
||
|
|
is used to remove one level of monadic structure, projecting its
|
||
|
|
bound argument into the outer level.</p></div></div><div class="top"><p class="src"><a id="v:foldM" class="def">foldM</a> :: (<a href="SafePrelude.html#t:Foldable">Foldable</a> t, <a href="SafePrelude.html#t:Monad">Monad</a> m) => (b -> a -> m b) -> b -> t a -> m b <a href="#v:foldM" class="selflink">#</a></p><div class="doc"><p>The <code><a href="SafePrelude.html#v:foldM">foldM</a></code> function is analogous to <code>foldl</code>, except that its result is
|
||
|
|
encapsulated in a monad. Note that <code><a href="SafePrelude.html#v:foldM">foldM</a></code> works from left-to-right over
|
||
|
|
the list arguments. This could be an issue where <code>(<code><a href="SafePrelude.html#v:-62--62-">>></a></code>)</code> and the `folded
|
||
|
|
function' are not commutative.</p><pre> foldM f a1 [x1, x2, ..., xm]</pre><p>==</p><pre> do
|
||
|
|
a2 <- f a1 x1
|
||
|
|
a3 <- f a2 x2
|
||
|
|
...
|
||
|
|
f am xm</pre><p>If right-to-left evaluation is required, the input list should be reversed.</p><p>Note: <code><a href="SafePrelude.html#v:foldM">foldM</a></code> is the same as <code><a href="SafePrelude.html#v:foldlM">foldlM</a></code></p></div></div><div class="top"><p class="src"><a id="v:foldM_" class="def">foldM_</a> :: (<a href="SafePrelude.html#t:Foldable">Foldable</a> t, <a href="SafePrelude.html#t:Monad">Monad</a> m) => (b -> a -> m b) -> b -> t a -> m () <a href="#v:foldM_" class="selflink">#</a></p><div class="doc"><p>Like <code><a href="SafePrelude.html#v:foldM">foldM</a></code>, but discards the result.</p></div></div><div class="top"><p class="src"><a id="v:replicateM_" class="def">replicateM_</a> :: <a href="SafePrelude.html#t:Applicative">Applicative</a> m => <a href="SafePrelude.html#t:Int">Int</a> -> m a -> m () <a href="#v:replicateM_" class="selflink">#</a></p><div class="doc"><p>Like <code><a href="../base-4.9.0.0/Control-Monad.html#v:replicateM">replicateM</a></code>, but discards the result.</p></div></div><div class="top"><p class="src"><a id="v:guard" class="def">guard</a> :: <a href="SafePrelude.html#t:Alternative">Alternative</a> f => <a href="SafePrelude.html#t:Bool">Bool</a> -> f () <a href="#v:guard" class="selflink">#</a></p><div class="doc"><p><code><code><a href="SafePrelude.html#v:guard">guard</a></code> b</code> is <code><code><a href="SafePrelude.html#v:pure">pure</a></code> ()</code> if <code>b</code> is <code><a href="SafePrelude.html#v:True">True</a></code>,
|
||
|
|
and <code><a href="SafePrelude.html#v:empty">empty</a></code> if <code>b</code> is <code><a href="SafePrelude.html#v:False">False</a></code>.</p></div></div><div class="top"><p class="src"><a id="v:when" class="def">when</a> :: <a href="SafePrelude.html#t:Applicative">Applicative</a> f => <a href="SafePrelude.html#t:Bool">Bool</a> -> f () -> f () <a href="#v:when" class="selflink">#</a></p><div class="doc"><p>Conditional execution of <code><a href="SafePrelude.html#t:Applicative">Applicative</a></code> expressions. For example,</p><pre>when debug (putStrLn "Debugging")</pre><p>will output the string <code>Debugging</code> if the Boolean value <code>debug</code>
|
||
|
|
is <code><a href="SafePrelude.html#v:True">True</a></code>, and otherwise do nothing.</p></div></div><div class="top"><p class="src"><a id="v:unless" class="def">unless</a> :: <a href="SafePrelude.html#t:Applicative">Applicative</a> f => <a href="SafePrelude.html#t:Bool">Bool</a> -> f () -> f () <a href="#v:unless" class="selflink">#</a></p><div class="doc"><p>The reverse of <code><a href="SafePrelude.html#v:when">when</a></code>.</p></div></div><div class="top"><p class="src"><a id="v:liftM" class="def">liftM</a> :: <a href="SafePrelude.html#t:Monad">Monad</a> m => (a1 -> r) -> m a1 -> m r <a href="#v:liftM" class="selflink">#</a></p><div class="doc"><p>Promote a function to a monad.</p></div></div><div class="top"><p class="src"><a id="v:ap" class="def">ap</a> :: <a href="SafePrelude.html#t:Monad">Monad</a> m => m (a -> b) -> m a -> m b <a href="#v:ap" class="selflink">#</a></p><div class="doc"><p>In many situations, the <code><a href="SafePrelude.html#v:liftM">liftM</a></code> operations can be replaced by uses of
|
||
|
|
<code><a href="SafePrelude.html#v:ap">ap</a></code>, which promotes function application.</p><pre> return f `ap` x1 `ap` ... `ap` xn</pre><p>is equivalent to</p><pre> liftMn f x1 x2 ... xn</pre></div></div><div class="top"><p class="src"><a id="v:-60--36--33--62-" class="def">(<$!>)</a> :: <a href="SafePrelude.html#t:Monad">Monad</a> m => (a -> b) -> m a -> m b <span class="fixity">infixl 4</span><span class="rightedge"></span> <a href="#v:-60--36--33--62-" class="selflink">#</a></p><div class="doc"><p>Strict version of <code><a href="SafePrelude.html#v:-60--36--62-"><$></a></code>.</p><p><em>Since: 4.8.0.0</em></p></div></div><h2 id="g:13">Concurrent</h2><div class="top"><p class="src"><a id="v:threadDelay" class="def">threadDelay</a> :: <a href="SafePrelude.html#t:Int">Int</a> -> <a href="SafePrelude.html#t:IO">IO</a> () <a href="#v:threadDelay" class="selflink">#</a></p><div class="doc"><p>Suspends the current thread for a given number of microseconds
|
||
|
|
(GHC only).</p><p>There is no guarantee that the thread will be rescheduled promptly
|
||
|
|
when the delay has expired, but the thread will never continue to
|
||
|
|
run <em>earlier</em> than specified.</p></div></div><div class="top"><p class="src"><span class="keyword">data</span> <a id="t:MVar" class="def">MVar</a> a :: <a href="../base-4.9.0.0/Data-Kind.html#t:-42-">*</a> -> <a href="../base-4.9.0.0/Data-Kind.html#t:-42-">*</a> <a href="#t:MVar" class="selflink">#</a></p><div class="doc"><p>An <code><a href="SafePrelude.html#t:MVar">MVar</a></code> (pronounced "em-var") is a synchronising variable, used
|
||
|
|
for communication between concurrent threads. It can be thought of
|
||
|
|
as a a box, which may be empty or full.</p></div><div class="subs instances"><p id="control.i:MVar" class="caption collapser" onclick="toggleSection('i:MVar')">Instances</p><div id="section.i:MVar" class="show"><table><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:id:MVar:Eq:1" class="instance expander" onclick="toggleSection('i:id:MVar:Eq:1')"></span> <a href="SafePrelude.html#t:Eq">Eq</a> (<a href="SafePrelude.html#t:MVar">MVar</a> a)</span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:id:MVar:Eq:1" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:-61--61-">(==)</a> :: <a href="SafePrelude.html#t:MVar">MVar</a> a -> <a href="SafePrelude.html#t:MVar">MVar</a> a -> <a href="SafePrelude.html#t:Bool">Bool</a> <a href="#v:-61--61-" class="selflink">#</a></p><p class="src"><a href="#v:-47--61-">(/=)</a> :: <a href="SafePrelude.html#t:MVar">MVar</a> a -> <a href="SafePrelude.html#t:MVar">MVar</a> a -> <a href="SafePrelude.html#t:Bool">Bool</a> <a href="#v:-47--61-" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:id:MVar:NFData:2" class="instance expander" onclick="toggleSection('i:id:MVar:NFData:2')"></span> <a href="SafePrelude.html#t:NFData">NFData</a> (<a href="SafePrelude.html#t:MVar">MVar</a> a)</span></td><td class="doc"><p><strong>NOTE</strong>: Only strict in the reference and not the referenced value.</p><p><em>Since: 1.4.2.0</em></p></td></tr><tr><td colspan="2"><div id="section.i:id:MVar:NFData:2" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:rnf">rnf</a> :: <a href="SafePrelude.html#t:MVar">MVar</a> a -> () <a href="#v:rnf" class="selflink">#</a></p></div></div></td></tr></table></div></div></div><div class="top"><p class="src"><a id="v:newEmptyMVar" class="def">newEmptyMVar</a> :: <a href="SafePrelude.html#t:IO">IO</a> (<a href="SafePrelude.html#t:MVar">MVar</a> a) <a href="#v:newEmptyMVar" class="selflink">#</a></p><div class="doc"><p>Create an <code><a href="SafePrelude.html#t:MVar">MVar</a></code> which is initially empty.</p></div></div><div class="top"><p class="src"><a id="v:newMVar" class="def">newMVar</a> :: a -> <a href="SafePrelude.html#t:IO">IO</a> (<a href="SafePrelude.html#t:MVar">MVar</a> a) <a href="#v:newMVar" class="selflink">#</a></p><div class="doc"><p>Create an <code><a href="SafePrelude.html#t:MVar">MVar</a></code> which contains the supplied value.</p></div></div><div class="top"><p class="src"><a id="v:takeMVar" class="def">takeMVar</a> :: <a href="SafePrelude.html#t:MVar">MVar</a> a -> <a href="SafePrelude.html#t:IO">IO</a> a <a href="#v:takeMVar" class="selflink">#</a></p><div class="doc"><p>Return the contents of the <code><a href="SafePrelude.html#t:MVar">MVar</a></code>. If the <code><a href="SafePrelude.html#t:MVar">MVar</a></code> is currently
|
||
|
|
empty, <code><a href="SafePrelude.html#v:takeMVar">takeMVar</a></code> will wait until it is full. After a <code><a href="SafePrelude.html#v:takeMVar">takeMVar</a></code>,
|
||
|
|
the <code><a href="SafePrelude.html#t:MVar">MVar</a></code> is left empty.</p><p>There are two further important properties of <code><a href="SafePrelude.html#v:takeMVar">takeMVar</a></code>:</p><ul><li><code><a href="SafePrelude.html#v:takeMVar">takeMVar</a></code> is single-wakeup. That is, if there are multiple
|
||
|
|
threads blocked in <code><a href="SafePrelude.html#v:takeMVar">takeMVar</a></code>, and the <code><a href="SafePrelude.html#t:MVar">MVar</a></code> becomes full,
|
||
|
|
only one thread will be woken up. The runtime guarantees that
|
||
|
|
the woken thread completes its <code><a href="SafePrelude.html#v:takeMVar">takeMVar</a></code> operation.</li><li>When multiple threads are blocked on an <code><a href="SafePrelude.html#t:MVar">MVar</a></code>, they are
|
||
|
|
woken up in FIFO order. This is useful for providing
|
||
|
|
fairness properties of abstractions built using <code><a href="SafePrelude.html#t:MVar">MVar</a></code>s.</li></ul></div></div><div class="top"><p class="src"><a id="v:putMVar" class="def">putMVar</a> :: <a href="SafePrelude.html#t:MVar">MVar</a> a -> a -> <a href="SafePrelude.html#t:IO">IO</a> () <a href="#v:putMVar" class="selflink">#</a></p><div class="doc"><p>Put a value into an <code><a href="SafePrelude.html#t:MVar">MVar</a></code>. If the <code><a href="SafePrelude.html#t:MVar">MVar</a></code> is currently full,
|
||
|
|
<code><a href="SafePrelude.html#v:putMVar">putMVar</a></code> will wait until it becomes empty.</p><p>There are two further important properties of <code><a href="SafePrelude.html#v:putMVar">putMVar</a></code>:</p><ul><li><code><a href="SafePrelude.html#v:putMVar">putMVar</a></code> is single-wakeup. That is, if there are multiple
|
||
|
|
threads blocked in <code><a href="SafePrelude.html#v:putMVar">putMVar</a></code>, and the <code><a href="SafePrelude.html#t:MVar">MVar</a></code> becomes empty,
|
||
|
|
only one thread will be woken up. The runtime guarantees that
|
||
|
|
the woken thread completes its <code><a href="SafePrelude.html#v:putMVar">putMVar</a></code> operation.</li><li>When multiple threads are blocked on an <code><a href="SafePrelude.html#t:MVar">MVar</a></code>, they are
|
||
|
|
woken up in FIFO order. This is useful for providing
|
||
|
|
fairness properties of abstractions built using <code><a href="SafePrelude.html#t:MVar">MVar</a></code>s.</li></ul></div></div><div class="top"><p class="src"><a id="v:readMVar" class="def">readMVar</a> :: <a href="SafePrelude.html#t:MVar">MVar</a> a -> <a href="SafePrelude.html#t:IO">IO</a> a <a href="#v:readMVar" class="selflink">#</a></p><div class="doc"><p>Atomically read the contents of an <code><a href="SafePrelude.html#t:MVar">MVar</a></code>. If the <code><a href="SafePrelude.html#t:MVar">MVar</a></code> is
|
||
|
|
currently empty, <code><a href="SafePrelude.html#v:readMVar">readMVar</a></code> will wait until its full.
|
||
|
|
<code><a href="SafePrelude.html#v:readMVar">readMVar</a></code> is guaranteed to receive the next <code><a href="SafePrelude.html#v:putMVar">putMVar</a></code>.</p><p><code><a href="SafePrelude.html#v:readMVar">readMVar</a></code> is multiple-wakeup, so when multiple readers are
|
||
|
|
blocked on an <code><a href="SafePrelude.html#t:MVar">MVar</a></code>, all of them are woken up at the same time.</p><p><em>Compatibility note:</em> Prior to base 4.7, <code><a href="SafePrelude.html#v:readMVar">readMVar</a></code> was a combination
|
||
|
|
of <code><a href="SafePrelude.html#v:takeMVar">takeMVar</a></code> and <code><a href="SafePrelude.html#v:putMVar">putMVar</a></code>. This mean that in the presence of
|
||
|
|
other threads attempting to <code><a href="SafePrelude.html#v:putMVar">putMVar</a></code>, <code><a href="SafePrelude.html#v:readMVar">readMVar</a></code> could block.
|
||
|
|
Furthermore, <code><a href="SafePrelude.html#v:readMVar">readMVar</a></code> would not receive the next <code><a href="SafePrelude.html#v:putMVar">putMVar</a></code> if there
|
||
|
|
was already a pending thread blocked on <code><a href="SafePrelude.html#v:takeMVar">takeMVar</a></code>. The old behavior
|
||
|
|
can be recovered by implementing 'readMVar as follows:</p><pre> readMVar :: MVar a -> IO a
|
||
|
|
readMVar m =
|
||
|
|
mask_ $ do
|
||
|
|
a <- takeMVar m
|
||
|
|
putMVar m a
|
||
|
|
return a
|
||
|
|
</pre></div></div><div class="top"><p class="src"><a id="v:swapMVar" class="def">swapMVar</a> :: <a href="SafePrelude.html#t:MVar">MVar</a> a -> a -> <a href="SafePrelude.html#t:IO">IO</a> a <a href="#v:swapMVar" class="selflink">#</a></p><div class="doc"><p>Take a value from an <code><a href="SafePrelude.html#t:MVar">MVar</a></code>, put a new value into the <code><a href="SafePrelude.html#t:MVar">MVar</a></code> and
|
||
|
|
return the value taken. This function is atomic only if there are
|
||
|
|
no other producers for this <code><a href="SafePrelude.html#t:MVar">MVar</a></code>.</p></div></div><div class="top"><p class="src"><a id="v:tryTakeMVar" class="def">tryTakeMVar</a> :: <a href="SafePrelude.html#t:MVar">MVar</a> a -> <a href="SafePrelude.html#t:IO">IO</a> (<a href="SafePrelude.html#t:Maybe">Maybe</a> a) <a href="#v:tryTakeMVar" class="selflink">#</a></p><div class="doc"><p>A non-blocking version of <code><a href="SafePrelude.html#v:takeMVar">takeMVar</a></code>. The <code><a href="SafePrelude.html#v:tryTakeMVar">tryTakeMVar</a></code> function
|
||
|
|
returns immediately, with <code><a href="SafePrelude.html#v:Nothing">Nothing</a></code> if the <code><a href="SafePrelude.html#t:MVar">MVar</a></code> was empty, or
|
||
|
|
<code><code><a href="SafePrelude.html#v:Just">Just</a></code> a</code> if the <code><a href="SafePrelude.html#t:MVar">MVar</a></code> was full with contents <code>a</code>. After <code><a href="SafePrelude.html#v:tryTakeMVar">tryTakeMVar</a></code>,
|
||
|
|
the <code><a href="SafePrelude.html#t:MVar">MVar</a></code> is left empty.</p></div></div><div class="top"><p class="src"><a id="v:tryPutMVar" class="def">tryPutMVar</a> :: <a href="SafePrelude.html#t:MVar">MVar</a> a -> a -> <a href="SafePrelude.html#t:IO">IO</a> <a href="SafePrelude.html#t:Bool">Bool</a> <a href="#v:tryPutMVar" class="selflink">#</a></p><div class="doc"><p>A non-blocking version of <code><a href="SafePrelude.html#v:putMVar">putMVar</a></code>. The <code><a href="SafePrelude.html#v:tryPutMVar">tryPutMVar</a></code> function
|
||
|
|
attempts to put the value <code>a</code> into the <code><a href="SafePrelude.html#t:MVar">MVar</a></code>, returning <code><a href="SafePrelude.html#v:True">True</a></code> if
|
||
|
|
it was successful, or <code><a href="SafePrelude.html#v:False">False</a></code> otherwise.</p></div></div><div class="top"><p class="src"><a id="v:isEmptyMVar" class="def">isEmptyMVar</a> :: <a href="SafePrelude.html#t:MVar">MVar</a> a -> <a href="SafePrelude.html#t:IO">IO</a> <a href="SafePrelude.html#t:Bool">Bool</a> <a href="#v:isEmptyMVar" class="selflink">#</a></p><div class="doc"><p>Check whether a given <code><a href="SafePrelude.html#t:MVar">MVar</a></code> is empty.</p><p>Notice that the boolean value returned is just a snapshot of
|
||
|
|
the state of the MVar. By the time you get to react on its result,
|
||
|
|
the MVar may have been filled (or emptied) - so be extremely
|
||
|
|
careful when using this operation. Use <code><a href="SafePrelude.html#v:tryTakeMVar">tryTakeMVar</a></code> instead if possible.</p></div></div><div class="top"><p class="src"><a id="v:withMVar" class="def">withMVar</a> :: <a href="SafePrelude.html#t:MVar">MVar</a> a -> (a -> <a href="SafePrelude.html#t:IO">IO</a> b) -> <a href="SafePrelude.html#t:IO">IO</a> b <a href="#v:withMVar" class="selflink">#</a></p><div class="doc"><p><code><a href="SafePrelude.html#v:withMVar">withMVar</a></code> is an exception-safe wrapper for operating on the contents
|
||
|
|
of an <code><a href="SafePrelude.html#t:MVar">MVar</a></code>. This operation is exception-safe: it will replace the
|
||
|
|
original contents of the <code><a href="SafePrelude.html#t:MVar">MVar</a></code> if an exception is raised (see
|
||
|
|
<a href="../base-4.9.0.0/Control-Exception.html">Control.Exception</a>). However, it is only atomic if there are no
|
||
|
|
other producers for this <code><a href="SafePrelude.html#t:MVar">MVar</a></code>.</p></div></div><div class="top"><p class="src"><a id="v:withMVarMasked" class="def">withMVarMasked</a> :: <a href="SafePrelude.html#t:MVar">MVar</a> a -> (a -> <a href="SafePrelude.html#t:IO">IO</a> b) -> <a href="SafePrelude.html#t:IO">IO</a> b <a href="#v:withMVarMasked" class="selflink">#</a></p><div class="doc"><p>Like <code><a href="SafePrelude.html#v:withMVar">withMVar</a></code>, but the <code>IO</code> action in the second argument is executed
|
||
|
|
with asynchronous exceptions masked.</p><p><em>Since: 4.7.0.0</em></p></div></div><div class="top"><p class="src"><a id="v:modifyMVar_" class="def">modifyMVar_</a> :: <a href="SafePrelude.html#t:MVar">MVar</a> a -> (a -> <a href="SafePrelude.html#t:IO">IO</a> a) -> <a href="SafePrelude.html#t:IO">IO</a> () <a href="#v:modifyMVar_" class="selflink">#</a></p><div class="doc"><p>An exception-safe wrapper for modifying the contents of an <code><a href="SafePrelude.html#t:MVar">MVar</a></code>.
|
||
|
|
Like <code><a href="SafePrelude.html#v:withMVar">withMVar</a></code>, <code><a href="SafePrelude.html#v:modifyMVar">modifyMVar</a></code> will replace the original contents of
|
||
|
|
the <code><a href="SafePrelude.html#t:MVar">MVar</a></code> if an exception is raised during the operation. This
|
||
|
|
function is only atomic if there are no other producers for this
|
||
|
|
<code><a href="SafePrelude.html#t:MVar">MVar</a></code>.</p></div></div><div class="top"><p class="src"><a id="v:modifyMVar" class="def">modifyMVar</a> :: <a href="SafePrelude.html#t:MVar">MVar</a> a -> (a -> <a href="SafePrelude.html#t:IO">IO</a> (a, b)) -> <a href="SafePrelude.html#t:IO">IO</a> b <a href="#v:modifyMVar" class="selflink">#</a></p><div class="doc"><p>A slight variation on <code><a href="SafePrelude.html#v:modifyMVar_">modifyMVar_</a></code> that allows a value to be
|
||
|
|
returned (<code>b</code>) in addition to the modified value of the <code><a href="SafePrelude.html#t:MVar">MVar</a></code>.</p></div></div><div class="top"><p class="src"><a id="v:modifyMVarMasked_" class="def">modifyMVarMasked_</a> :: <a href="SafePrelude.html#t:MVar">MVar</a> a -> (a -> <a href="SafePrelude.html#t:IO">IO</a> a) -> <a href="SafePrelude.html#t:IO">IO</a> () <a href="#v:modifyMVarMasked_" class="selflink">#</a></p><div class="doc"><p>Like <code><a href="SafePrelude.html#v:modifyMVar_">modifyMVar_</a></code>, but the <code>IO</code> action in the second argument is executed with
|
||
|
|
asynchronous exceptions masked.</p><p><em>Since: 4.6.0.0</em></p></div></div><div class="top"><p class="src"><a id="v:modifyMVarMasked" class="def">modifyMVarMasked</a> :: <a href="SafePrelude.html#t:MVar">MVar</a> a -> (a -> <a href="SafePrelude.html#t:IO">IO</a> (a, b)) -> <a href="SafePrelude.html#t:IO">IO</a> b <a href="#v:modifyMVarMasked" class="selflink">#</a></p><div class="doc"><p>Like <code><a href="SafePrelude.html#v:modifyMVar">modifyMVar</a></code>, but the <code>IO</code> action in the second argument is executed with
|
||
|
|
asynchronous exceptions masked.</p><p><em>Since: 4.6.0.0</em></p></div></div><div class="top"><p class="src"><a id="v:tryReadMVar" class="def">tryReadMVar</a> :: <a href="SafePrelude.html#t:MVar">MVar</a> a -> <a href="SafePrelude.html#t:IO">IO</a> (<a href="SafePrelude.html#t:Maybe">Maybe</a> a) <a href="#v:tryReadMVar" class="selflink">#</a></p><div class="doc"><p>A non-blocking version of <code><a href="SafePrelude.html#v:readMVar">readMVar</a></code>. The <code><a href="SafePrelude.html#v:tryReadMVar">tryReadMVar</a></code> function
|
||
|
|
returns immediately, with <code><a href="SafePrelude.html#v:Nothing">Nothing</a></code> if the <code><a href="SafePrelude.html#t:MVar">MVar</a></code> was empty, or
|
||
|
|
<code><code><a href="SafePrelude.html#v:Just">Just</a></code> a</code> if the <code><a href="SafePrelude.html#t:MVar">MVar</a></code> was full with contents <code>a</code>.</p><p><em>Since: 4.7.0.0</em></p></div></div><div class="top"><p class="src"><a id="v:mkWeakMVar" class="def">mkWeakMVar</a> :: <a href="SafePrelude.html#t:MVar">MVar</a> a -> <a href="SafePrelude.html#t:IO">IO</a> () -> <a href="SafePrelude.html#t:IO">IO</a> (<a href="../base-4.9.0.0/System-Mem-Weak.html#t:Weak">Weak</a> (<a href="SafePrelude.html#t:MVar">MVar</a> a)) <a href="#v:mkWeakMVar" class="selflink">#</a></p><div class="doc"><p>Make a <code><a href="../base-4.9.0.0/System-Mem-Weak.html#t:Weak">Weak</a></code> pointer to an <code><a href="SafePrelude.html#t:MVar">MVar</a></code>, using the second argument as
|
||
|
|
a finalizer to run when <code><a href="SafePrelude.html#t:MVar">MVar</a></code> is garbage-collected</p><p><em>Since: 4.6.0.0</em></p></div></div><div class="top"><p class="src"><span class="keyword">data</span> <a id="t:Chan" class="def">Chan</a> a :: <a href="../base-4.9.0.0/Data-Kind.html#t:-42-">*</a> -> <a href="../base-4.9.0.0/Data-Kind.html#t:-42-">*</a> <a href="#t:Chan" class="selflink">#</a></p><div class="doc"><p><code><a href="SafePrelude.html#t:Chan">Chan</a></code> is an abstract type representing an unbounded FIFO channel.</p></div><div class="subs instances"><p id="control.i:Chan" class="caption collapser" onclick="toggleSection('i:Chan')">Instances</p><div id="section.i:Chan" class="show"><table><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:id:Chan:Eq:1" class="instance expander" onclick="toggleSection('i:id:Chan:Eq:1')"></span> <a href="SafePrelude.html#t:Eq">Eq</a> (<a href="SafePrelude.html#t:Chan">Chan</a> a)</span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:id:Chan:Eq:1" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:-61--61-">(==)</a> :: <a href="SafePrelude.html#t:Chan">Chan</a> a -> <a href="SafePrelude.html#t:Chan">Chan</a> a -> <a href="SafePrelude.html#t:Bool">Bool</a> <a href="#v:-61--61-" class="selflink">#</a></p><p class="src"><a href="#v:-47--61-">(/=)</a> :: <a href="SafePrelude.html#t:Chan">Chan</a> a -> <a href="SafePrelude.html#t:Chan">Chan</a> a -> <a href="SafePrelude.html#t:Bool">Bool</a> <a href="#v:-47--61-" class="selflink">#</a></p></div></div></td></tr></table></div></div></div><div class="top"><p class="src"><a id="v:newChan" class="def">newChan</a> :: <a href="SafePrelude.html#t:IO">IO</a> (<a href="SafePrelude.html#t:Chan">Chan</a> a) <a href="#v:newChan" class="selflink">#</a></p><div class="doc"><p>Build and returns a new instance of <code><a href="SafePrelude.html#t:Chan">Chan</a></code>.</p></div></div><div class="top"><p class="src"><a id="v:writeChan" class="def">writeChan</a> :: <a href="SafePrelude.html#t:Chan">Chan</a> a -> a -> <a href="SafePrelude.html#t:IO">IO</a> () <a href="#v:writeChan" class="selflink">#</a></p><div class="doc"><p>Write a value to a <code><a href="SafePrelude.html#t:Chan">Chan</a></code>.</p></div></div><div class="top"><p class="src"><a id="v:readChan" class="def">readChan</a> :: <a href="SafePrelude.html#t:Chan">Chan</a> a -> <a href="SafePrelude.html#t:IO">IO</a> a <a href="#v:readChan" class="selflink">#</a></p><div class="doc"><p>Read the next value from the <code><a href="SafePrelude.html#t:Chan">Chan</a></code>.</p></div></div><div class="top"><p class="src"><a id="v:dupChan" class="def">dupChan</a> :: <a href="SafePrelude.html#t:Chan">Chan</a> a -> <a href="SafePrelude.html#t:IO">IO</a> (<a href="SafePrelude.html#t:Chan">Chan</a> a) <a href="#v:dupChan" class="selflink">#</a></p><div class="doc"><p>Duplicate a <code><a href="SafePrelude.html#t:Chan">Chan</a></code>: the duplicate channel begins empty, but data written to
|
||
|
|
either channel from then on will be available from both. Hence this creates
|
||
|
|
a kind of broadcast channel, where data written by anyone is seen by
|
||
|
|
everyone else.</p><p>(Note that a duplicated channel is not equal to its original.
|
||
|
|
So: <code>fmap (c /=) $ dupChan c</code> returns <code>True</code> for all <code>c</code>.)</p></div></div><h2 id="g:14">Reader</h2><div class="top"><p class="src"><a id="v:asks" class="def">asks</a> <a href="#v:asks" class="selflink">#</a></p><div class="subs arguments"><p class="caption">Arguments</p><table><tr><td class="src">:: <a href="SafePrelude.html#t:MonadReader">MonadReader</a> r m</td><td class="doc empty"> </td></tr><tr><td class="src">=> (r -> a)</td><td class="doc"><p>The selector function to apply to the environment.</p></td></tr><tr><td class="src">-> m a</td><td class="doc empty"> </td></tr></table></div><div class="doc"><p>Retrieves a function of the current environment.</p></div></div><h2 id="g:15">Exceptions</h2><div class="top"><p class="src"><a id="v:throwIO" class="def">throwIO</a> :: (<a href="SafePrelude.html#t:MonadThrow">MonadThrow</a> m, <a href="SafePrelude.html#t:Exception">Exception</a> e) => e -> m a <a href="#v:throwIO" class="selflink">#</a></p><div class="doc"><p>Synonym for <code><a href="../safe-exceptions-0.1.4.0/Control-Exception-Safe.html#v:throw">throw</a></code></p><p><em>Since: 0.1.0.0</em></p></div></div><div class="top"><p class="src"><a id="v:throwM" class="def">throwM</a> :: (<a href="SafePrelude.html#t:MonadThrow">MonadThrow</a> m, <a href="SafePrelude.html#t:Exception">Exception</a> e) => e -> m a <a href="#v:throwM" class="selflink">#</a></p><div class="doc"><p>Synonym for <code><a href="../safe-exceptions-0.1.4.0/Control-Exception-Safe.html#v:throw">throw</a></code></p><p><em>Since: 0.1.0.0</em></p></div></div><div class="top"><p class="src"><a id="v:throwTo" class="def">throwTo</a> :: (<a href="SafePrelude.html#t:Exception">Exception</a> e, <a href="SafePrelude.html#t:MonadIO">MonadIO</a> m) => <a href="../base-4.9.0.0/Control-Concurrent.html#t:ThreadId">ThreadId</a> -> e -> m () <a href="#v:throwTo" class="selflink">#</a></p><div class="doc"><p>Throw an asynchronous exception to another thread</p><p>It's usually a better idea to use the async package, see
|
||
|
|
<a href="https://github.com/fpco/safe-exceptions#quickstart">https://github.com/fpco/safe-exceptions#quickstart</a></p><p><em>Since: 0.1.0.0</em></p></div></div><div class="top"><p class="src"><a id="v:catch" class="def">catch</a> :: (<a href="SafePrelude.html#t:MonadCatch">MonadCatch</a> m, <a href="SafePrelude.html#t:Exception">Exception</a> e) => m a -> (e -> m a) -> m a <a href="#v:catch" class="selflink">#</a></p><div class="doc"><p>Same as upstream <code><a href="../exceptions-0.8.3/Control-Monad-Catch.html#v:catch">catch</a></code>, but will not catch asynchronous
|
||
|
|
exceptions</p><p><em>Since: 0.1.0.0</em></p></div></div><div class="top"><p class="src"><a id="v:catchIO" class="def">catchIO</a> :: <a href="SafePrelude.html#t:MonadCatch">MonadCatch</a> m => m a -> (<a href="../base-4.9.0.0/Control-Exception-Base.html#t:IOException">IOException</a> -> m a) -> m a <a href="#v:catchIO" class="selflink">#</a></p><div class="doc"><p><code><a href="../exceptions-0.8.3/Control-Monad-Catch.html#v:catch">catch</a></code> specialized to only catching <code><a href="../base-4.9.0.0/Control-Exception-Base.html#t:IOException">IOException</a></code>s</p><p><em>Since: 0.1.3.0</em></p></div></div><div class="top"><p class="src"><a id="v:catchAny" class="def">catchAny</a> :: <a href="SafePrelude.html#t:MonadCatch">MonadCatch</a> m => m a -> (<a href="SafePrelude.html#t:SomeException">SomeException</a> -> m a) -> m a <a href="#v:catchAny" class="selflink">#</a></p><div class="doc"><p><code><a href="SafePrelude.html#v:catch">catch</a></code> specialized to catch all synchronous exception</p><p><em>Since: 0.1.0.0</em></p></div></div><div class="top"><p class="src"><a id="v:catchDeep" class="def">catchDeep</a> :: (<a href="SafePrelude.html#t:MonadCatch">MonadCatch</a> m, <a href="SafePrelude.html#t:MonadIO">MonadIO</a> m, <a href="SafePrelude.html#t:Exception">Exception</a> e, <a href="SafePrelude.html#t:NFData">NFData</a> a) => m a -> (e -> m a) -> m a <a href="#v:catchDeep" class="selflink">#</a></p><div class="doc"><p>Same as <code><a href="SafePrelude.html#v:catch">catch</a></code>, but fully force evaluation of the result value
|
||
|
|
to find all impure exceptions.</p><p><em>Since: 0.1.1.0</em></p></div></div><div class="top"><p class="src"><a id="v:catchAnyDeep" class="def">catchAnyDeep</a> :: (<a href="SafePrelude.html#t:MonadCatch">MonadCatch</a> m, <a href="SafePrelude.html#t:MonadIO">MonadIO</a> m, <a href="SafePrelude.html#t:NFData">NFData</a> a) => m a -> (<a href="SafePrelude.html#t:SomeException">SomeException</a> -> m a) -> m a <a href="#v:catchAnyDeep" class="selflink">#</a></p><div class="doc"><p><code><a href="SafePrelude.html#v:catchDeep">catchDeep</a></code> specialized to catch all synchronous exception</p><p><em>Since: 0.1.1.0</em></p></div></div><div class="top"><p class="src"><a id="v:handle" class="def">handle</a> :: (<a href="SafePrelude.html#t:MonadCatch">MonadCatch</a> m, <a href="SafePrelude.html#t:Exception">Exception</a> e) => (e -> m a) -> m a -> m a <a href="#v:handle" class="selflink">#</a></p><div class="doc"><p>Flipped version of <code><a href="SafePrelude.html#v:catch">catch</a></code></p><p><em>Since: 0.1.0.0</em></p></div></div><div class="top"><p class="src"><a id="v:handleIO" class="def">handleIO</a> :: <a href="SafePrelude.html#t:MonadCatch">MonadCatch</a> m => (<a href="../base-4.9.0.0/Control-Exception-Base.html#t:IOException">IOException</a> -> m a) -> m a -> m a <a href="#v:handleIO" class="selflink">#</a></p><div class="doc"><p><code><a href="../exceptions-0.8.3/Control-Monad-Catch.html#v:handle">handle</a></code> specialized to only catching <code><a href="../base-4.9.0.0/Control-Exception-Base.html#t:IOException">IOException</a></code>s</p><p><em>Since: 0.1.3.0</em></p></div></div><div class="top"><p class="src"><a id="v:handleAny" class="def">handleAny</a> :: <a href="SafePrelude.html#t:MonadCatch">MonadCatch</a> m => (<a href="SafePrelude.html#t:SomeException">SomeException</a> -> m a) -> m a -> m a <a href="#v:handleAny" class="selflink">#</a></p><div class="doc"><p>Flipped version of <code><a href="SafePrelude.html#v:catchAny">catchAny</a></code></p><p><em>Since: 0.1.0.0</em></p></div></div><div class="top"><p class="src"><a id="v:handleDeep" class="def">handleDeep</a> :: (<a href="SafePrelude.html#t:MonadCatch">MonadCatch</a> m, <a href="SafePrelude.html#t:Exception">Exception</a> e, <a href="SafePrelude.html#t:MonadIO">MonadIO</a> m, <a href="SafePrelude.html#t:NFData">NFData</a> a) => (e -> m a) -> m a -> m a <a href="#v:handleDeep" class="selflink">#</a></p><div class="doc"><p>Flipped version of <code><a href="SafePrelude.html#v:catchDeep">catchDeep</a></code></p><p><em>Since: 0.1.1.0</em></p></div></div><div class="top"><p class="src"><a id="v:handleAnyDeep" class="def">handleAnyDeep</a> :: (<a href="SafePrelude.html#t:MonadCatch">MonadCatch</a> m, <a href="SafePrelude.html#t:MonadIO">MonadIO</a> m, <a href="SafePrelude.html#t:NFData">NFData</a> a) => (<a href="SafePrelude.html#t:SomeException">SomeException</a> -> m a) -> m a -> m a <a href="#v:handleAnyDeep" class="selflink">#</a></p><div class="doc"><p>Flipped version of <code><a href="SafePrelude.html#v:catchAnyDeep">catchAnyDeep</a></code></p><p><em>Since: 0.1.1.0</em></p></div></div><div class="top"><p class="src"><a id="v:try" class="def">try</a> :: (<a href="SafePrelude.html#t:MonadCatch">MonadCatch</a> m, <a href="SafePrelude.html#t:Exception">Exception</a> e) => m a -> m (<a href="SafePrelude.html#t:Either">Either</a> e a) <a href="#v:try" class="selflink">#</a></p><div class="doc"><p>Same as upstream <code><a href="../exceptions-0.8.3/Control-Monad-Catch.html#v:try">try</a></code>, but will not catch asynchronous
|
||
|
|
exceptions</p><p><em>Since: 0.1.0.0</em></p></div></div><div class="top"><p class="src"><a id="v:tryIO" class="def">tryIO</a> :: <a href="SafePrelude.html#t:MonadCatch">MonadCatch</a> m => m a -> m (<a href="SafePrelude.html#t:Either">Either</a> <a href="../base-4.9.0.0/Control-Exception-Base.html#t:IOException">IOException</a> a) <a href="#v:tryIO" class="selflink">#</a></p><div class="doc"><p><code><a href="../exceptions-0.8.3/Control-Monad-Catch.html#v:try">try</a></code> specialized to only catching <code><a href="../base-4.9.0.0/Control-Exception-Base.html#t:IOException">IOException</a></code>s</p><p><em>Since: 0.1.3.0</em></p></div></div><div class="top"><p class="src"><a id="v:tryAny" class="def">tryAny</a> :: <a href="SafePrelude.html#t:MonadCatch">MonadCatch</a> m => m a -> m (<a href="SafePrelude.html#t:Either">Either</a> <a href="SafePrelude.html#t:SomeException">SomeException</a> a) <a href="#v:tryAny" class="selflink">#</a></p><div class="doc"><p><code><a href="SafePrelude.html#v:try">try</a></code> specialized to catch all synchronous exceptions</p><p><em>Since: 0.1.0.0</em></p></div></div><div class="top"><p class="src"><a id="v:tryDeep" class="def">tryDeep</a> :: (<a href="SafePrelude.html#t:MonadCatch">MonadCatch</a> m, <a href="SafePrelude.html#t:MonadIO">MonadIO</a> m, <a href="SafePrelude.html#t:Exception">Exception</a> e, <a href="SafePrelude.html#t:NFData">NFData</a> a) => m a -> m (<a href="SafePrelude.html#t:Either">Either</a> e a) <a href="#v:tryDeep" class="selflink">#</a></p><div class="doc"><p>Same as <code><a href="SafePrelude.html#v:try">try</a></code>, but fully force evaluation of the result value
|
||
|
|
to find all impure exceptions.</p><p><em>Since: 0.1.1.0</em></p></div></div><div class="top"><p class="src"><a id="v:tryAnyDeep" class="def">tryAnyDeep</a> :: (<a href="SafePrelude.html#t:MonadCatch">MonadCatch</a> m, <a href="SafePrelude.html#t:MonadIO">MonadIO</a> m, <a href="SafePrelude.html#t:NFData">NFData</a> a) => m a -> m (<a href="SafePrelude.html#t:Either">Either</a> <a href="SafePrelude.html#t:SomeException">SomeException</a> a) <a href="#v:tryAnyDeep" class="selflink">#</a></p><div class="doc"><p><code><a href="SafePrelude.html#v:tryDeep">tryDeep</a></code> specialized to catch all synchronous exceptions</p><p><em>Since: 0.1.1.0</em></p></div></div><div class="top"><p class="src"><a id="v:onException" class="def">onException</a> :: <a href="SafePrelude.html#t:MonadMask">MonadMask</a> m => m a -> m b -> m a <a href="#v:onException" class="selflink">#</a></p><div class="doc"><p>Async safe version of <code><a href="../base-4.9.0.0/Control-Exception-Base.html#v:onException">onException</a></code></p><p><em>Since: 0.1.0.0</em></p></div></div><div class="top"><p class="src"><a id="v:bracket" class="def">bracket</a> :: <a href="SafePrelude.html#t:MonadMask">MonadMask</a> m => m a -> (a -> m b) -> (a -> m c) -> m c <a href="#v:bracket" class="selflink">#</a></p><div class="doc"><p>Async safe version of <code><a href="../base-4.9.0.0/Control-Exception-Base.html#v:bracket">bracket</a></code></p><p><em>Since: 0.1.0.0</em></p></div></div><div class="top"><p class="src"><a id="v:bracket_" class="def">bracket_</a> :: <a href="SafePrelude.html#t:MonadMask">MonadMask</a> m => m a -> m b -> m c -> m c <a href="#v:bracket_" class="selflink">#</a></p><div class="doc"><p>Async safe version of <code><a href="../base-4.9.0.0/Control-Exception-Base.html#v:bracket_">bracket_</a></code></p><p><em>Since: 0.1.0.0</em></p></div></div><div class="top"><p class="src"><a id="v:finally" class="def">finally</a> :: <a href="SafePrelude.html#t:MonadMask">MonadMask</a> m => m a -> m b -> m a <a href="#v:finally" class="selflink">#</a></p><div class="doc"><p>Async safe version of <code><a href="../base-4.9.0.0/Control-Exception-Base.html#v:finally">finally</a></code></p><p><em>Since: 0.1.0.0</em></p></div></div><div class="top"><p class="src"><a id="v:withException" class="def">withException</a> :: (<a href="SafePrelude.html#t:MonadMask">MonadMask</a> m, <a href="SafePrelude.html#t:Exception">Exception</a> e) => m a -> (e -> m b) -> m a <a href="#v:withException" class="selflink">#</a></p><div class="doc"><p>Like <code><a href="SafePrelude.html#v:onException">onException</a></code>, but provides the handler the thrown
|
||
|
|
exception.</p><p><em>Since: 0.1.0.0</em></p></div></div><div class="top"><p class="src"><a id="v:bracketOnError" class="def">bracketOnError</a> :: <a href="SafePrelude.html#t:MonadMask">MonadMask</a> m => m a -> (a -> m b) -> (a -> m c) -> m c <a href="#v:bracketOnError" class="selflink">#</a></p><div class="doc"><p>Async safe version of <code><a href="../base-4.9.0.0/Control-Exception-Base.html#v:bracketOnError">bracketOnError</a></code></p><p><em>Since: 0.1.0.0</em></p></div></div><div class="top"><p class="src"><a id="v:bracketOnError_" class="def">bracketOnError_</a> :: <a href="SafePrelude.html#t:MonadMask">MonadMask</a> m => m a -> m b -> m c -> m c <a href="#v:bracketOnError_" class="selflink">#</a></p><div class="doc"><p>Async safe version of <code><a href="E.html#v:bracketOnError_">bracketOnError_</a></code></p><p><em>Since: 0.1.0.0</em></p></div></div><div class="top"><p class="src"><a id="v:displayException" class="def">displayException</a> :: <a href="SafePrelude.html#t:Exception">Exception</a> e => e -> <a href="SafePrelude.html#t:String">String</a> <a href="#v:displayException" class="selflink">#</a></p><div class="doc"><p>Render this exception value in a human-friendly manner.</p><p>Default implementation: <code><code><a href="SafePrelude.html#v:show">show</a></code></code>.</p><p><em>Since: 4.8.0.0</em></p></div></div><h2 id="g:16">Arrow</h2><div class="top"><p class="src"><a id="v:-38--38--38-" class="def">(&&&)</a> :: <a href="../base-4.9.0.0/Control-Arrow.html#t:Arrow">Arrow</a> a => <span class="keyword">forall</span> b c c'. a b c -> a b c' -> a b (c, c') <a href="#v:-38--38--38-" class="selflink">#</a></p><div class="doc"><p>Fanout: send the input to both argument arrows and combine
|
||
|
|
their output.</p><p>The default definition may be overridden with a more efficient
|
||
|
|
version if desired.</p></div></div><div class="top"><p class="src"><a id="v:-42--42--42-" class="def">(***)</a> :: <a href="../base-4.9.0.0/Control-Arrow.html#t:Arrow">Arrow</a> a => <span class="keyword">forall</span> b c b' c'. a b c -> a b' c' -> a (b, b') (c, c') <a href="#v:-42--42--42-" class="selflink">#</a></p><div class="doc"><p>Split the input between the two argument arrows and combine
|
||
|
|
their output. Note that this is in general not a functor.</p><p>The default definition may be overridden with a more efficient
|
||
|
|
version if desired.</p></div></div><h2 id="g:17">Maybe</h2><div class="top"><p class="src"><a id="v:mapMaybe" class="def">mapMaybe</a> :: (a -> <a href="SafePrelude.html#t:Maybe">Maybe</a> b) -> [a] -> [b] <a href="#v:mapMaybe" class="selflink">#</a></p><div class="doc"><p>The <code><a href="SafePrelude.html#v:mapMaybe">mapMaybe</a></code> function is a version of <code><a href="../base-4.9.0.0/GHC-OldList.html#v:map">map</a></code> which can throw
|
||
|
|
out elements. In particular, the functional argument returns
|
||
|
|
something of type <code><code><a href="SafePrelude.html#t:Maybe">Maybe</a></code> b</code>. If this is <code><a href="SafePrelude.html#v:Nothing">Nothing</a></code>, no element
|
||
|
|
is added on to the result list. If it is <code><code><a href="SafePrelude.html#v:Just">Just</a></code> b</code>, then <code>b</code> is
|
||
|
|
included in the result list.</p><h4 id="control.ch:mapMaybe0" class="caption expander" onclick="toggleSection('ch:mapMaybe0')">Examples</h4><div id="section.ch:mapMaybe0" class="hide"><p>Using <code><code><a href="SafePrelude.html#v:mapMaybe">mapMaybe</a></code> f x</code> is a shortcut for <code><code><a href="SafePrelude.html#v:catMaybes">catMaybes</a></code> $ <code><a href="../base-4.9.0.0/GHC-OldList.html#v:map">map</a></code> f x</code>
|
||
|
|
in most cases:</p><pre class="screen"><code class="prompt">>>> </code><strong class="userinput"><code>import Text.Read ( readMaybe )
|
||
|
|
</code></strong><code class="prompt">>>> </code><strong class="userinput"><code>let readMaybeInt = readMaybe :: String -> Maybe Int
|
||
|
|
</code></strong><code class="prompt">>>> </code><strong class="userinput"><code>mapMaybe readMaybeInt ["1", "Foo", "3"]
|
||
|
|
</code></strong>[1,3]
|
||
|
|
<code class="prompt">>>> </code><strong class="userinput"><code>catMaybes $ map readMaybeInt ["1", "Foo", "3"]
|
||
|
|
</code></strong>[1,3]
|
||
|
|
</pre><p>If we map the <code><a href="SafePrelude.html#v:Just">Just</a></code> constructor, the entire list should be returned:</p><pre class="screen"><code class="prompt">>>> </code><strong class="userinput"><code>mapMaybe Just [1,2,3]
|
||
|
|
</code></strong>[1,2,3]
|
||
|
|
</pre></div></div></div><div class="top"><p class="src"><a id="v:catMaybes" class="def">catMaybes</a> :: [<a href="SafePrelude.html#t:Maybe">Maybe</a> a] -> [a] <a href="#v:catMaybes" class="selflink">#</a></p><div class="doc"><p>The <code><a href="SafePrelude.html#v:catMaybes">catMaybes</a></code> function takes a list of <code><a href="SafePrelude.html#t:Maybe">Maybe</a></code>s and returns
|
||
|
|
a list of all the <code><a href="SafePrelude.html#v:Just">Just</a></code> values.</p><h4 id="control.ch:catMaybes0" class="caption expander" onclick="toggleSection('ch:catMaybes0')">Examples</h4><div id="section.ch:catMaybes0" class="hide"><p>Basic usage:</p><pre class="screen"><code class="prompt">>>> </code><strong class="userinput"><code>catMaybes [Just 1, Nothing, Just 3]
|
||
|
|
</code></strong>[1,3]
|
||
|
|
</pre><p>When constructing a list of <code><a href="SafePrelude.html#t:Maybe">Maybe</a></code> values, <code><a href="SafePrelude.html#v:catMaybes">catMaybes</a></code> can be used
|
||
|
|
to return all of the "success" results (if the list is the result
|
||
|
|
of a <code><a href="../base-4.9.0.0/GHC-OldList.html#v:map">map</a></code>, then <code><a href="SafePrelude.html#v:mapMaybe">mapMaybe</a></code> would be more appropriate):</p><pre class="screen"><code class="prompt">>>> </code><strong class="userinput"><code>import Text.Read ( readMaybe )
|
||
|
|
</code></strong><code class="prompt">>>> </code><strong class="userinput"><code>[readMaybe x :: Maybe Int | x <- ["1", "Foo", "3"] ]
|
||
|
|
</code></strong>[Just 1,Nothing,Just 3]
|
||
|
|
<code class="prompt">>>> </code><strong class="userinput"><code>catMaybes $ [readMaybe x :: Maybe Int | x <- ["1", "Foo", "3"] ]
|
||
|
|
</code></strong>[1,3]
|
||
|
|
</pre></div></div></div><div class="top"><p class="src"><a id="v:fromMaybe" class="def">fromMaybe</a> :: a -> <a href="SafePrelude.html#t:Maybe">Maybe</a> a -> a <a href="#v:fromMaybe" class="selflink">#</a></p><div class="doc"><p>The <code><a href="SafePrelude.html#v:fromMaybe">fromMaybe</a></code> function takes a default value and and <code><a href="SafePrelude.html#t:Maybe">Maybe</a></code>
|
||
|
|
value. If the <code><a href="SafePrelude.html#t:Maybe">Maybe</a></code> is <code><a href="SafePrelude.html#v:Nothing">Nothing</a></code>, it returns the default values;
|
||
|
|
otherwise, it returns the value contained in the <code><a href="SafePrelude.html#t:Maybe">Maybe</a></code>.</p><h4 id="control.ch:fromMaybe0" class="caption expander" onclick="toggleSection('ch:fromMaybe0')">Examples</h4><div id="section.ch:fromMaybe0" class="hide"><p>Basic usage:</p><pre class="screen"><code class="prompt">>>> </code><strong class="userinput"><code>fromMaybe "" (Just "Hello, World!")
|
||
|
|
</code></strong>"Hello, World!"
|
||
|
|
</pre><pre class="screen"><code class="prompt">>>> </code><strong class="userinput"><code>fromMaybe "" Nothing
|
||
|
|
</code></strong>""
|
||
|
|
</pre><p>Read an integer from a string using <code>readMaybe</code>. If we fail to
|
||
|
|
parse an integer, we want to return <code>0</code> by default:</p><pre class="screen"><code class="prompt">>>> </code><strong class="userinput"><code>import Text.Read ( readMaybe )
|
||
|
|
</code></strong><code class="prompt">>>> </code><strong class="userinput"><code>fromMaybe 0 (readMaybe "5")
|
||
|
|
</code></strong>5
|
||
|
|
<code class="prompt">>>> </code><strong class="userinput"><code>fromMaybe 0 (readMaybe "")
|
||
|
|
</code></strong>0
|
||
|
|
</pre></div></div></div><div class="top"><p class="src"><a id="v:isJust" class="def">isJust</a> :: <a href="SafePrelude.html#t:Maybe">Maybe</a> a -> <a href="SafePrelude.html#t:Bool">Bool</a> <a href="#v:isJust" class="selflink">#</a></p><div class="doc"><p>The <code><a href="SafePrelude.html#v:isJust">isJust</a></code> function returns <code><a href="SafePrelude.html#v:True">True</a></code> iff its argument is of the
|
||
|
|
form <code>Just _</code>.</p><h4 id="control.ch:isJust0" class="caption expander" onclick="toggleSection('ch:isJust0')">Examples</h4><div id="section.ch:isJust0" class="hide"><p>Basic usage:</p><pre class="screen"><code class="prompt">>>> </code><strong class="userinput"><code>isJust (Just 3)
|
||
|
|
</code></strong>True
|
||
|
|
</pre><pre class="screen"><code class="prompt">>>> </code><strong class="userinput"><code>isJust (Just ())
|
||
|
|
</code></strong>True
|
||
|
|
</pre><pre class="screen"><code class="prompt">>>> </code><strong class="userinput"><code>isJust Nothing
|
||
|
|
</code></strong>False
|
||
|
|
</pre><p>Only the outer constructor is taken into consideration:</p><pre class="screen"><code class="prompt">>>> </code><strong class="userinput"><code>isJust (Just Nothing)
|
||
|
|
</code></strong>True
|
||
|
|
</pre></div></div></div><div class="top"><p class="src"><a id="v:isNothing" class="def">isNothing</a> :: <a href="SafePrelude.html#t:Maybe">Maybe</a> a -> <a href="SafePrelude.html#t:Bool">Bool</a> <a href="#v:isNothing" class="selflink">#</a></p><div class="doc"><p>The <code><a href="SafePrelude.html#v:isNothing">isNothing</a></code> function returns <code><a href="SafePrelude.html#v:True">True</a></code> iff its argument is <code><a href="SafePrelude.html#v:Nothing">Nothing</a></code>.</p><h4 id="control.ch:isNothing0" class="caption expander" onclick="toggleSection('ch:isNothing0')">Examples</h4><div id="section.ch:isNothing0" class="hide"><p>Basic usage:</p><pre class="screen"><code class="prompt">>>> </code><strong class="userinput"><code>isNothing (Just 3)
|
||
|
|
</code></strong>False
|
||
|
|
</pre><pre class="screen"><code class="prompt">>>> </code><strong class="userinput"><code>isNothing (Just ())
|
||
|
|
</code></strong>False
|
||
|
|
</pre><pre class="screen"><code class="prompt">>>> </code><strong class="userinput"><code>isNothing Nothing
|
||
|
|
</code></strong>True
|
||
|
|
</pre><p>Only the outer constructor is taken into consideration:</p><pre class="screen"><code class="prompt">>>> </code><strong class="userinput"><code>isNothing (Just Nothing)
|
||
|
|
</code></strong>False
|
||
|
|
</pre></div></div></div><div class="top"><p class="src"><a id="v:listToMaybe" class="def">listToMaybe</a> :: [a] -> <a href="SafePrelude.html#t:Maybe">Maybe</a> a <a href="#v:listToMaybe" class="selflink">#</a></p><div class="doc"><p>The <code><a href="SafePrelude.html#v:listToMaybe">listToMaybe</a></code> function returns <code><a href="SafePrelude.html#v:Nothing">Nothing</a></code> on an empty list
|
||
|
|
or <code><code><a href="SafePrelude.html#v:Just">Just</a></code> a</code> where <code>a</code> is the first element of the list.</p><h4 id="control.ch:listToMaybe0" class="caption expander" onclick="toggleSection('ch:listToMaybe0')">Examples</h4><div id="section.ch:listToMaybe0" class="hide"><p>Basic usage:</p><pre class="screen"><code class="prompt">>>> </code><strong class="userinput"><code>listToMaybe []
|
||
|
|
</code></strong>Nothing
|
||
|
|
</pre><pre class="screen"><code class="prompt">>>> </code><strong class="userinput"><code>listToMaybe [9]
|
||
|
|
</code></strong>Just 9
|
||
|
|
</pre><pre class="screen"><code class="prompt">>>> </code><strong class="userinput"><code>listToMaybe [1,2,3]
|
||
|
|
</code></strong>Just 1
|
||
|
|
</pre><p>Composing <code><a href="../base-4.9.0.0/Data-Maybe.html#v:maybeToList">maybeToList</a></code> with <code><a href="SafePrelude.html#v:listToMaybe">listToMaybe</a></code> should be the identity
|
||
|
|
on singleton/empty lists:</p><pre class="screen"><code class="prompt">>>> </code><strong class="userinput"><code>maybeToList $ listToMaybe [5]
|
||
|
|
</code></strong>[5]
|
||
|
|
<code class="prompt">>>> </code><strong class="userinput"><code>maybeToList $ listToMaybe []
|
||
|
|
</code></strong>[]
|
||
|
|
</pre><p>But not on lists with more than one element:</p><pre class="screen"><code class="prompt">>>> </code><strong class="userinput"><code>maybeToList $ listToMaybe [1,2,3]
|
||
|
|
</code></strong>[1]
|
||
|
|
</pre></div></div></div><h2 id="g:18">Either</h2><div class="top"><p class="src"><a id="v:partitionEithers" class="def">partitionEithers</a> :: [<a href="SafePrelude.html#t:Either">Either</a> a b] -> ([a], [b]) <a href="#v:partitionEithers" class="selflink">#</a></p><div class="doc"><p>Partitions a list of <code><a href="SafePrelude.html#t:Either">Either</a></code> into two lists.
|
||
|
|
All the <code><a href="SafePrelude.html#v:Left">Left</a></code> elements are extracted, in order, to the first
|
||
|
|
component of the output. Similarly the <code><a href="SafePrelude.html#v:Right">Right</a></code> elements are extracted
|
||
|
|
to the second component of the output.</p><h4 id="control.ch:partitionEithers0" class="caption expander" onclick="toggleSection('ch:partitionEithers0')">Examples</h4><div id="section.ch:partitionEithers0" class="hide"><p>Basic usage:</p><pre class="screen"><code class="prompt">>>> </code><strong class="userinput"><code>let list = [ Left "foo", Right 3, Left "bar", Right 7, Left "baz" ]
|
||
|
|
</code></strong><code class="prompt">>>> </code><strong class="userinput"><code>partitionEithers list
|
||
|
|
</code></strong>(["foo","bar","baz"],[3,7])
|
||
|
|
</pre><p>The pair returned by <code><code><a href="SafePrelude.html#v:partitionEithers">partitionEithers</a></code> x</code> should be the same
|
||
|
|
pair as <code>(<code><a href="SafePrelude.html#v:lefts">lefts</a></code> x, <code><a href="SafePrelude.html#v:rights">rights</a></code> x)</code>:</p><pre class="screen"><code class="prompt">>>> </code><strong class="userinput"><code>let list = [ Left "foo", Right 3, Left "bar", Right 7, Left "baz" ]
|
||
|
|
</code></strong><code class="prompt">>>> </code><strong class="userinput"><code>partitionEithers list == (lefts list, rights list)
|
||
|
|
</code></strong>True
|
||
|
|
</pre></div></div></div><div class="top"><p class="src"><a id="v:lefts" class="def">lefts</a> :: [<a href="SafePrelude.html#t:Either">Either</a> a b] -> [a] <a href="#v:lefts" class="selflink">#</a></p><div class="doc"><p>Extracts from a list of <code><a href="SafePrelude.html#t:Either">Either</a></code> all the <code><a href="SafePrelude.html#v:Left">Left</a></code> elements.
|
||
|
|
All the <code><a href="SafePrelude.html#v:Left">Left</a></code> elements are extracted in order.</p><h4 id="control.ch:lefts0" class="caption expander" onclick="toggleSection('ch:lefts0')">Examples</h4><div id="section.ch:lefts0" class="hide"><p>Basic usage:</p><pre class="screen"><code class="prompt">>>> </code><strong class="userinput"><code>let list = [ Left "foo", Right 3, Left "bar", Right 7, Left "baz" ]
|
||
|
|
</code></strong><code class="prompt">>>> </code><strong class="userinput"><code>lefts list
|
||
|
|
</code></strong>["foo","bar","baz"]
|
||
|
|
</pre></div></div></div><div class="top"><p class="src"><a id="v:rights" class="def">rights</a> :: [<a href="SafePrelude.html#t:Either">Either</a> a b] -> [b] <a href="#v:rights" class="selflink">#</a></p><div class="doc"><p>Extracts from a list of <code><a href="SafePrelude.html#t:Either">Either</a></code> all the <code><a href="SafePrelude.html#v:Right">Right</a></code> elements.
|
||
|
|
All the <code><a href="SafePrelude.html#v:Right">Right</a></code> elements are extracted in order.</p><h4 id="control.ch:rights0" class="caption expander" onclick="toggleSection('ch:rights0')">Examples</h4><div id="section.ch:rights0" class="hide"><p>Basic usage:</p><pre class="screen"><code class="prompt">>>> </code><strong class="userinput"><code>let list = [ Left "foo", Right 3, Left "bar", Right 7, Left "baz" ]
|
||
|
|
</code></strong><code class="prompt">>>> </code><strong class="userinput"><code>rights list
|
||
|
|
</code></strong>[3,7]
|
||
|
|
</pre></div></div></div><h2 id="g:19">Ord</h2><div class="top"><p class="src"><a id="v:on" class="def">on</a> :: (b -> b -> c) -> (a -> b) -> a -> a -> c <span class="fixity">infixl 0</span><span class="rightedge"></span> <a href="#v:on" class="selflink">#</a></p><div class="doc"><p><code>(*) `on` f = \x y -> f x * f y</code>.</p><p>Typical usage: <code><code><a href="../base-4.9.0.0/Data-List.html#v:sortBy">sortBy</a></code> (<code>compare</code> `on` <code>fst</code>)</code>.</p><p>Algebraic properties:</p><ul><li><code>(*) `on` <code><a href="SafePrelude.html#v:id">id</a></code> = (*)</code> (if <code>(*) ∉ {⊥, <code><a href="SafePrelude.html#v:const">const</a></code> ⊥}</code>)</li><li><pre>((*) `on` f) `on` g = (*) `on` (f . g)</pre></li><li><pre><code><a href="SafePrelude.html#v:flip">flip</a></code> on f . <code><a href="SafePrelude.html#v:flip">flip</a></code> on g = <code><a href="SafePrelude.html#v:flip">flip</a></code> on (g . f)</pre></li></ul></div></div><div class="top"><p class="src"><a id="v:comparing" class="def">comparing</a> :: <a href="SafePrelude.html#t:Ord">Ord</a> a => (b -> a) -> b -> b -> <a href="SafePrelude.html#t:Ordering">Ordering</a> <a href="#v:comparing" class="selflink">#</a></p><div class="doc"><pre>comparing p x y = compare (p x) (p y)</pre><p>Useful combinator for use in conjunction with the <code>xxxBy</code> family
|
||
|
|
of functions from <a href="../base-4.9.0.0/Data-List.html">Data.List</a>, for example:</p><pre> ... sortBy (comparing fst) ...</pre></div></div><h2 id="g:20">Say</h2><div class="top"><p class="src"><a id="v:say" class="def">say</a> :: <a href="SafePrelude.html#t:MonadIO">MonadIO</a> m => <a href="SafePrelude.html#t:Text">Text</a> -> m () <a href="#v:say" class="selflink">#</a></p><div class="doc"><p>Send a <code><a href="SafePrelude.html#t:Text">Text</a></code> to standard output, appending a newline, and chunking the
|
||
|
|
data. By default, the chunk size is 2048 characters, so any messages below
|
||
|
|
that size will be sent as one contiguous unit. If larger messages are used,
|
||
|
|
it is possible for interleaving with other threads to occur.</p><p><em>Since: 0.1.0.0</em></p></div></div><div class="top"><p class="src"><a id="v:sayString" class="def">sayString</a> :: <a href="SafePrelude.html#t:MonadIO">MonadIO</a> m => <a href="SafePrelude.html#t:String">String</a> -> m () <a href="#v:sayString" class="selflink">#</a></p><div class="doc"><p>Same as <code><a href="SafePrelude.html#v:say">say</a></code>, but operates on a <code><a href="SafePrelude.html#t:String">String</a></code>. Note that this will
|
||
|
|
force the entire <code>String</code> into memory at once, and will fail for
|
||
|
|
infinite <code>String</code>s.</p><p><em>Since: 0.1.0.0</em></p></div></div><div class="top"><p class="src"><a id="v:sayShow" class="def">sayShow</a> :: (<a href="SafePrelude.html#t:MonadIO">MonadIO</a> m, <a href="SafePrelude.html#t:Show">Show</a> a) => a -> m () <a href="#v:sayShow" class="selflink">#</a></p><div class="doc"><p>Same as <code><a href="SafePrelude.html#v:say">say</a></code>, but for instances of <code><a href="SafePrelude.html#t:Show">Show</a></code>.</p><p>If your <code>Show</code> instance generates infinite output, this will fail. However,
|
||
|
|
an infinite result for <code>show</code> would generally be considered an invalid
|
||
|
|
instance anyway.</p><p><em>Since: 0.1.0.0</em></p></div></div><div class="top"><p class="src"><a id="v:sayErr" class="def">sayErr</a> :: <a href="SafePrelude.html#t:MonadIO">MonadIO</a> m => <a href="SafePrelude.html#t:Text">Text</a> -> m () <a href="#v:sayErr" class="selflink">#</a></p><div class="doc"><p>Same as <code><a href="SafePrelude.html#v:say">say</a></code>, but data is sent to standard error.</p><p><em>Since: 0.1.0.0</em></p></div></div><div class="top"><p class="src"><a id="v:sayErrString" class="def">sayErrString</a> :: <a href="SafePrelude.html#t:MonadIO">MonadIO</a> m => <a href="SafePrelude.html#t:String">String</a> -> m () <a href="#v:sayErrString" class="selflink">#</a></p><div class="doc"><p>Same as <code><a href="SafePrelude.html#v:sayString">sayString</a></code>, but data is sent to standard error.</p><p><em>Since: 0.1.0.0</em></p></div></div><div class="top"><p class="src"><a id="v:sayErrShow" class="def">sayErrShow</a> :: (<a href="SafePrelude.html#t:MonadIO">MonadIO</a> m, <a href="SafePrelude.html#t:Show">Show</a> a) => a -> m () <a href="#v:sayErrShow" class="selflink">#</a></p><div class="doc"><p>Same as <code><a href="SafePrelude.html#v:sayShow">sayShow</a></code>, but data is sent to standard error.</p><p><em>Since: 0.1.0.0</em></p></div></div><div class="top"><p class="src"><a id="v:hSay" class="def">hSay</a> :: <a href="SafePrelude.html#t:MonadIO">MonadIO</a> m => <a href="SafePrelude.html#t:Handle">Handle</a> -> <a href="SafePrelude.html#t:Text">Text</a> -> m () <a href="#v:hSay" class="selflink">#</a></p><div class="doc"><p>Same as <code><a href="SafePrelude.html#v:say">say</a></code>, but data is sent to the provided <code><a href="SafePrelude.html#t:Handle">Handle</a></code>.</p><p><em>Since: 0.1.0.0</em></p></div></div><div class="top"><p class="src"><a id="v:hSayString" class="def">hSayString</a> :: <a href="SafePrelude.html#t:MonadIO">MonadIO</a> m => <a href="SafePrelude.html#t:Handle">Handle</a> -> <a href="SafePrelude.html#t:String">String</a> -> m () <a href="#v:hSayString" class="selflink">#</a></p><div class="doc"><p>Same as <code><a href="SafePrelude.html#v:sayString">sayString</a></code>, but data is sent to the provided <code><a href="SafePrelude.html#t:Handle">Handle</a></code>.</p><p><em>Since: 0.1.0.0</em></p></div></div><div class="top"><p class="src"><a id="v:hSayShow" class="def">hSayShow</a> :: (<a href="SafePrelude.html#t:MonadIO">MonadIO</a> m, <a href="SafePrelude.html#t:Show">Show</a> a) => <a href="SafePrelude.html#t:Handle">Handle</a> -> a -> m () <a href="#v:hSayShow" class="selflink">#</a></p><div class="doc"><p>Same as <code><a href="SafePrelude.html#v:sayShow">sayShow</a></code>, but data is sent to the provided <code><a href="SafePrelude.html#t:Handle">Handle</a></code>.</p><p><em>Since: 0.1.0.0</em></p></div></div><h2 id="g:21">IORef</h2><div class="top"><p class="src"><span class="keyword">data</span> <a id="t:IORef" class="def">IORef</a> a :: <a href="../base-4.9.0.0/Data-Kind.html#t:-42-">*</a> -> <a href="../base-4.9.0.0/Data-Kind.html#t:-42-">*</a> <a href="#t:IORef" class="selflink">#</a></p><div class="doc"><p>A mutable variable in the <code><a href="SafePrelude.html#t:IO">IO</a></code> monad</p></div><div class="subs instances"><p id="control.i:IORef" class="caption collapser" onclick="toggleSection('i:IORef')">Instances</p><div id="section.i:IORef" class="show"><table><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:id:IORef:Eq:1" class="instance expander" onclick="toggleSection('i:id:IORef:Eq:1')"></span> <a href="SafePrelude.html#t:Eq">Eq</a> (<a href="SafePrelude.html#t:IORef">IORef</a> a)</span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:id:IORef:Eq:1" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:-61--61-">(==)</a> :: <a href="SafePrelude.html#t:IORef">IORef</a> a -> <a href="SafePrelude.html#t:IORef">IORef</a> a -> <a href="SafePrelude.html#t:Bool">Bool</a> <a hre
|
||
|
|
means if the program calls <code><a href="SafePrelude.html#v:modifyIORef">modifyIORef</a></code> many times, but seldomly uses the
|
||
|
|
value, thunks will pile up in memory resulting in a space leak. This is a
|
||
|
|
common mistake made when using an IORef as a counter. For example, the
|
||
|
|
following will likely produce a stack overflow:</p><pre>ref <- newIORef 0
|
||
|
|
replicateM_ 1000000 $ modifyIORef ref (+1)
|
||
|
|
readIORef ref >>= print</pre><p>To avoid this problem, use <code><a href="SafePrelude.html#v:modifyIORef-39-">modifyIORef'</a></code> instead.</p></div></div><div class="top"><p class="src"><a id="v:modifyIORef-39-" class="def">modifyIORef'</a> :: <a href="SafePrelude.html#t:IORef">IORef</a> a -> (a -> a) -> <a href="SafePrelude.html#t:IO">IO</a> () <a href="#v:modifyIORef-39-" class="selflink">#</a></p><div class="doc"><p>Strict version of <code><a href="SafePrelude.html#v:modifyIORef">modifyIORef</a></code></p><p><em>Since: 4.6.0.0</em></p></div></div><div class="top"><p class="src"><a id="v:atomicModifyIORef" class="def">atomicModifyIORef</a> :: <a href="SafePrelude.html#t:IORef">IORef</a> a -> (a -> (a, b)) -> <a href="SafePrelude.html#t:IO">IO</a> b <a href="#v:atomicModifyIORef" class="selflink">#</a></p><div class="doc"><p>Atomically modifies the contents of an <code><a href="SafePrelude.html#t:IORef">IORef</a></code>.</p><p>This function is useful for using <code><a href="SafePrelude.html#t:IORef">IORef</a></code> in a safe way in a multithreaded
|
||
|
|
program. If you only have one <code><a href="SafePrelude.html#t:IORef">IORef</a></code>, then using <code><a href="SafePrelude.html#v:atomicModifyIORef">atomicModifyIORef</a></code> to
|
||
|
|
access and modify it will prevent race conditions.</p><p>Extending the atomicity to multiple <code><a href="SafePrelude.html#t:IORef">IORef</a></code>s is problematic, so it
|
||
|
|
is recommended that if you need to do anything more complicated
|
||
|
|
then using <code><a href="../base-4.9.0.0/Control-Concurrent-MVar.html#v:MVar">MVar</a></code> instead is a good idea.</p><p><code><a href="SafePrelude.html#v:atomicModifyIORef">atomicModifyIORef</a></code> does not apply the function strictly. This is important
|
||
|
|
to know even if all you are doing is replacing the value. For example, this
|
||
|
|
will leak memory:</p><pre>ref <- newIORef '1'
|
||
|
|
forever $ atomicModifyIORef ref (\_ -> ('2', ()))</pre><p>Use <code><a href="SafePrelude.html#v:atomicModifyIORef-39-">atomicModifyIORef'</a></code> or <code><a href="SafePrelude.html#v:atomicWriteIORef">atomicWriteIORef</a></code> to avoid this problem.</p></div></div><div class="top"><p class="src"><a id="v:atomicModifyIORef-39-" class="def">atomicModifyIORef'</a> :: <a href="SafePrelude.html#t:IORef">IORef</a> a -> (a -> (a, b)) -> <a href="SafePrelude.html#t:IO">IO</a> b <a href="#v:atomicModifyIORef-39-" class="selflink">#</a></p><div class="doc"><p>Strict version of <code><a href="SafePrelude.html#v:atomicModifyIORef">atomicModifyIORef</a></code>. This forces both the value stored
|
||
|
|
in the <code><a href="SafePrelude.html#t:IORef">IORef</a></code> as well as the value returned.</p><p><em>Since: 4.6.0.0</em></p></div></div><div class="top"><p class="src"><a id="v:atomicWriteIORef" class="def">atomicWriteIORef</a> :: <a href="SafePrelude.html#t:IORef">IORef</a> a -> a -> <a href="SafePrelude.html#t:IO">IO</a> () <a href="#v:atomicWriteIORef" class="selflink">#</a></p><div class="doc"><p>Variant of <code><a href="SafePrelude.html#v:writeIORef">writeIORef</a></code> with the "barrier to reordering" property that
|
||
|
|
<code><a href="SafePrelude.html#v:atomicModifyIORef">atomicModifyIORef</a></code> has.</p><p><em>Since: 4.6.0.0</em></p></div></div><div class="top"><p class="src"><a id="v:mkWeakIORef" class="def">mkWeakIORef</a> :: <a href="SafePrelude.html#t:IORef">IORef</a> a -> <a href="SafePrelude.html#t:IO">IO</a> () -> <a href="SafePrelude.html#t:IO">IO</a> (<a href="../base-4.9.0.0/System-Mem-Weak.html#t:Weak">Weak</a> (<a href="SafePrelude.html#t:IORef">IORef</a> a)) <a href="#v:mkWeakIORef" class="selflink">#</a></p><div class="doc"><p>Make a <code><a href="../base-4.9.0.0/System-Mem-Weak.html#t:Weak">Weak</a></code> pointer to an <code><a href="SafePrelude.html#t:IORef">IORef</a></code>, using the second argument as a finalizer
|
||
|
|
to run when <code><a href="SafePrelude.html#t:IORef">IORef</a></code> is garbage-collected</p></div></div><h2 id="g:22">IO</h2><div class="top"><p class="src"><span class="keyword">data</span> <a id="t:Handle" class="def">Handle</a> :: <a href="../base-4.9.0.0/Data-Kind.html#t:-42-">*</a> <a href="#t:Handle" class="selflink">#</a></p><div class="doc"><p>Haskell defines operations to read and write characters from and to files,
|
||
|
|
represented by values of type <code>Handle</code>. Each value of this type is a
|
||
|
|
<em>handle</em>: a record used by the Haskell run-time system to <em>manage</em> I/O
|
||
|
|
with file system objects. A handle has at least the following properties:</p><ul><li>whether it manages input or output or both;</li><li>whether it is <em>open</em>, <em>closed</em> or <em>semi-closed</em>;</li><li>whether the object is seekable;</li><li>whether buffering is disabled, or enabled on a line or block basis;</li><li>a buffer (whose length may be zero).</li></ul><p>Most handles will also have a current I/O position indicating where the next
|
||
|
|
input or output operation will occur. A handle is <em>readable</em> if it
|
||
|
|
manages only input or both input and output; likewise, it is <em>writable</em> if
|
||
|
|
it manages only output or both input and output. A handle is <em>open</em> when
|
||
|
|
first allocated.
|
||
|
|
Once it is closed it can no longer be used for either input or output,
|
||
|
|
though an implementation cannot re-use its storage while references
|
||
|
|
remain to it. Handles are in the <code><a href="SafePrelude.html#t:Show">Show</a></code> and <code><a href="SafePrelude.html#t:Eq">Eq</a></code> classes. The string
|
||
|
|
produced by showing a handle is system dependent; it should include
|
||
|
|
enough information to identify the handle for debugging. A handle is
|
||
|
|
equal according to <code><a href="SafePrelude.html#v:-61--61-">==</a></code> only to itself; no attempt
|
||
|
|
is made to compare the internal state of different handles for equality.</p></div><div class="subs instances"><p id="control.i:Handle" class="caption collapser" onclick="toggleSection('i:Handle')">Instances</p><div id="section.i:Handle" class="show"><table><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:id:Handle:Eq:1" class="instance expander" onclick="toggleSection('i:id:Handle:Eq:1')"></span> <a href="SafePrelude.html#t:Eq">Eq</a> <a href="SafePrelude.html#t:Handle">Handle</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:id:Handle:Eq:1" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:-61--61-">(==)</a> :: <a href="SafePrelude.html#t:Handle">Handle</a> -> <a href="SafePrelude.html#t:Handle">Handle</a> -> <a href="SafePrelude.html#t:Bool">Bool</a> <a href="#v:-61--61-" class="selflink">#</a></p><p class="src"><a href="#v:-47--61-">(/=)</a> :: <a href="SafePrelude.html#t:Handle">Handle</a> -> <a href="SafePrelude.html#t:Handle">Handle</a> -> <a href="SafePrelude.html#t:Bool">Bool</a> <a href="#v:-47--61-" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:id:Handle:Show:2" class="instance expander" onclick="toggleSection('i:id:Handle:Show:2')"></span> <a href="SafePrelude.html#t:Show">Show</a> <a href="SafePrelude.html#t:Handle">Handle</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:id:Handle:Show:2" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:showsPrec">showsPrec</a> :: <a href="SafePrelude.html#t:Int">Int</a> -> <a href="SafePrelude.html#t:Handle">Handle</a> -> <a href="../base-4.9.0.0/Text-Show.html#t:ShowS">ShowS</a> <a href="#v:showsPrec" class="selflink">#</a></p><p class="src"><a href="#v:show">show</a> :: <a href="SafePrelude.html#t:Handle">Handle</a> -> <a href="SafePrelude.html#t:String">String</a> <a href="#v:show" class="selflink">#</a></p><p class="src"><a href="#v:showList">showList</a> :: [<a href="SafePrelude.html#t:Handle">Handle</a>] -> <a href="../base-4.9.0.0/Text-Show.html#t:ShowS">ShowS</a> <a href="#v:showList" class="selflink">#</a></p></div></div></td></tr></table></div></div></div><div class="top"><p class="src"><span class="keyword">data</span> <a id="t:IOMode" class="def">IOMode</a> :: <a href="../base-4.9.0.0/Data-Kind.html#t:-42-">*</a> <a href="#t:IOMode" class="selflink">#</a></p><div class="doc"><p>See <code><a href="../base-4.9.0.0/System-IO.html#v:openFile">openFile</a></code></p></div><div class="subs constructors"><p class="caption">Constructors</p><table><tr><td class="src"><a id="v:ReadMode" class="def">ReadMode</a></td><td class="doc empty"> </td></tr><tr><td class="src"><a id="v:WriteMode" class="def">WriteMode</a></td><td class="doc empty"> </td></tr><tr><td class="src"><a id="v:AppendMode" class="def">AppendMode</a></td><td class="doc empty"> </td></tr><tr><td class="src"><a id="v:ReadWriteMode" class="def">ReadWriteMode</a></td><td class="doc empty"> </td></tr></table></div><div class="subs instances"><p id="control.i:IOMode" class="caption collapser" onclick="toggleSection('i:IOMode')">Instances</p><div id="section.i:IOMode" class="show"><table><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:id:IOMode:Enum:1" class="instance expander" onclick="toggleSection('i:id:IOMode:Enum:1')"></span> <a href="../base-4.9.0.0/Prelude.html#t:Enum">Enum</a> <a href="SafePrelude.html#t:IOMode">IOMode</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:id:IOMode:Enum:1" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:succ">succ</a> :: <a href="SafePrelude.html#t:IOMode">IOMode</a> -> <a href="SafePrelude.html#t:IOMode">IOMode</a> <a href="#v:succ" class="selflink">#</a></p><p class="src"><a href="#v:pred">pred</a> :: <a
|
||
|
|
computation finishes, if <code>hdl</code> is writable its buffer is flushed as
|
||
|
|
for <code><a href="../base-4.9.0.0/GHC-IO-Handle.html#v:hFlush">hFlush</a></code>.
|
||
|
|
Performing <code><a href="SafePrelude.html#v:hClose">hClose</a></code> on a handle that has already been closed has no effect;
|
||
|
|
doing so is not an error. All other operations on a closed handle will fail.
|
||
|
|
If <code><a href="SafePrelude.html#v:hClose">hClose</a></code> fails for any reason, any further operations (apart from
|
||
|
|
<code><a href="SafePrelude.html#v:hClose">hClose</a></code>) on the handle will still fail as if <code>hdl</code> had been successfully
|
||
|
|
closed.</p></div></div><div class="top"><p class="src"><a id="v:withBinaryFile" class="def">withBinaryFile</a> :: <a href="SafePrelude.html#t:FilePath">FilePath</a> -> <a href="SafePrelude.html#t:IOMode">IOMode</a> -> (<a href="SafePrelude.html#t:Handle">Handle</a> -> <a href="SafePrelude.html#t:IO">IO</a> r) -> <a href="SafePrelude.html#t:IO">IO</a> r <a href="#v:withBinaryFile" class="selflink">#</a></p><div class="doc"><p><code><code><a href="SafePrelude.html#v:withBinaryFile">withBinaryFile</a></code> name mode act</code> opens a file using <code><a href="../base-4.9.0.0/GHC-IO-Handle-FD.html#v:openBinaryFile">openBinaryFile</a></code>
|
||
|
|
and passes the resulting handle to the computation <code>act</code>. The handle
|
||
|
|
will be closed on exit from <code><a href="SafePrelude.html#v:withBinaryFile">withBinaryFile</a></code>, whether by normal
|
||
|
|
termination or by raising an exception.</p></div></div><div class="top"><p class="src"><a id="v:readFile" class="def">readFile</a> :: <a href="SafePrelude.html#t:FilePath">FilePath</a> -> <a href="SafePrelude.html#t:IO">IO</a> <a href="SafePrelude.html#t:ByteString">ByteString</a> <a href="#v:readFile" class="selflink">#</a></p><div class="doc"><p>Read an entire file strictly into a <code><a href="SafePrelude.html#t:ByteString">ByteString</a></code>.</p></div></div><div class="top"><p class="src"><a id="v:writeFile" class="def">writeFile</a> :: <a href="SafePrelude.html#t:FilePath">FilePath</a> -> <a href="SafePrelude.html#t:ByteString">ByteString</a> -> <a href="SafePrelude.html#t:IO">IO</a> () <a href="#v:writeFile" class="selflink">#</a></p><div class="doc"><p>Write a <code><a href="SafePrelude.html#t:ByteString">ByteString</a></code> to a file.</p></div></div><div class="top"><p class="src"><a id="v:readFileUtf8" class="def">readFileUtf8</a> :: <a href="SafePrelude.html#t:MonadIO">MonadIO</a> m => <a href="SafePrelude.html#t:FilePath">FilePath</a> -> m <a href="SafePrelude.html#t:Text">Text</a> <a href="src/SafePrelude.html#readFileUtf8" class="link">Source</a> <a href="#v:readFileUtf8" class="selflink">#</a></p><div class="doc"><p>Read a file assuming a UTF-8 character encoding.</p><p>This leverages <code><a href="SafePrelude.html#v:decodeUtf8">decodeUtf8</a></code>, so in the event of a character
|
||
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encoding issue, replacement characters will be used.</p><p><em>Since: 0.1.0.0</em></p></div></div><div class="top"><p class="src"><a id="v:writeFileUtf8" class="def">writeFileUtf8</a> :: <a href="SafePrelude.html#t:MonadIO">MonadIO</a> m => <a href="SafePrelude.html#t:FilePath">FilePath</a> -> <a href="SafePrelude.html#t:Text">Text</a> -> m () <a href="src/SafePrelude.html#writeFileUtf8" class="link">Source</a> <a href="#v:writeFileUtf8" class="selflink">#</a></p><div class="doc"><p>Write a file using a UTF-8 character encoding.</p><p><em>Since: 0.1.0.0</em></p></div></div><h2 id="g:23">Character encoding</h2><div class="top"><p class="src"><a id="v:encodeUtf8" class="def">encodeUtf8</a> :: <a href="SafePrelude.html#t:Text">Text</a> -> <a href="SafePrelude.html#t:ByteString">ByteString</a> <a href="#v:encodeUtf8" class="selflink">#</a></p><div class="doc"><p>Encode text using UTF-8 encoding.</p></div></div><div class="top"><p class="src"><a id="v:decodeUtf8" class="def">decodeUtf8</a> :: <a href="SafePrelude.html#t:ByteString">ByteString</a> -> <a href="SafePrelude.html#t:Text">Text</a> <a href="src/SafePrelude.html#decodeUtf8" class="link">Source</a> <a href="#v:decodeUtf8" class="selflink">#</a></p><div class="doc"><p>A total function for decoding a <code><a href="SafePrelude.html#t:ByteString">ByteString</a></code> into <code><a href="SafePrelude.html#t:Text">Text</a></code> using a
|
||
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UTF-8 character encoding. This uses <code><a href="../text-1.2.2.1/Data-Text-Encoding-Error.html#v:lenientDecode">lenientDecode</a></code> in the case of
|
||
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any encoding errors.</p><p><em>Since: 0.1.0.0</em></p></div></div><h2 id="g:24">deepseq</h2><div class="top"><p class="src"><span class="keyword">class</span> <a id="t:NFData" class="def">NFData</a> a <span class="keyword">where</span> <a href="#t:NFData" class="selflink">#</a></p><div class="doc"><p>A class of types that can be fully evaluated.</p><p><em>Since: 1.1.0.0</em></p></div><div class="subs minimal"><p class="caption">Minimal complete definition</p><p class="src">Nothing</p></div><div class="subs instances"><p id="control.i:NFData" class="caption collapser" onclick="toggleSection('i:NFData')">Instances</p><div id="section.i:NFData" class="show"><table><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:NFData:NFData:1" class="instance expander" onclick="toggleSection('i:ic:NFData:NFData:1')"></span> <a href="SafePrelude.html#t:NFData">NFData</a> <a href="SafePrelude.html#t:Bool">Bool</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:NFData:NFData:1" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:rnf">rnf</a> :: <a href="SafePrelude.html#t:Bool">Bool</a> -> () <a href="#v:rnf" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:NFData:NFData:2" class="instance expander" onclick="toggleSection('i:ic:NFData:NFData:2')"></span> <a href="SafePrelude.html#t:NFData">NFData</a> <a href="SafePrelude.html#t:Char">Char</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:NFData:NFData:2" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:rnf">rnf</a> :: <a href="SafePrelude.html#t:Char">Char</a> -> () <a href="#v:rnf" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:NFData:NFData:3" class="instance expander" onclick="toggleSection('i:ic:NFData:NFData:3')"></span> <a href="SafePrelude.html#t:NFData">NFData</a> <a href="SafePrelude.html#t:Double">Double</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:NFData:NFData:3" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:rnf">rnf</a> :: <a href="SafePrelude.html#t:Double">Double</a> -> () <a href="#v:rnf" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:NFData:NFData:4" class="instance expander" onclick="toggleSection('i:ic:NFData:NFData:4')"></span> <a href="SafePrelude.html#t:NFData">NFData</a> <a href="SafePrelude.html#t:Float">Float</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:NFData:NFData:4" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:rnf">rnf</a> :: <a href="SafePrelude.html#t:Float">Float</a> -> () <a href="#v:rnf" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:NFData:NFData:5" class="instance expander" onclick="toggleSection('i:ic:NFData:NFData:5')"></span> <a href="SafePrelude.html#t:NFData">NFData</a> <a href="SafePrelude.html#t:Int">Int</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:NFData:NFData:5" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:rnf">rnf</a> :: <a href="SafePrelude.html#t:Int">Int</a> -> () <a href="#v:rnf" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:NFData:NFData:6" class="instance expander" onclick="toggleSection('i:ic:NFData:NFData:6')"></span> <a href="SafePrelude.html#t:NFData">NFData</a> <a href="SafePrelude.html#t:Int8">Int8</a></span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id
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This assumes that WHNF is equivalent to NF for functions.</p><p><em>Since: 1.3.0.0</em></p></td></tr><tr><td colspan="2"><div id="section.i:ic:NFData:NFData:95" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:rnf">rnf</a> :: (a -> b) -> () <a href="#v:rnf" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:NFData:NFData:96" class="instance expander" onclick="toggleSection('i:ic:NFData:NFData:96')"></span> (<a href="SafePrelude.html#t:NFData">NFData</a> a, <a href="SafePrelude.html#t:NFData">NFData</a> b) => <a href="SafePrelude.html#t:NFData">NFData</a> (<a href="SafePrelude.html#t:Either">Either</a> a b)</span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:NFData:NFData:96" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:rnf">rnf</a> :: <a href="SafePrelude.html#t:Either">Either</a> a b -> () <a href="#v:rnf" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:NFData:NFData:97" class="instance expander" onclick="toggleSection('i:ic:NFData:NFData:97')"></span> (<a href="SafePrelude.html#t:NFData">NFData</a> a, <a href="SafePrelude.html#t:NFData">NFData</a> b) => <a href="SafePrelude.html#t:NFData">NFData</a> (a, b)</span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:NFData:NFData:97" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:rnf">rnf</a> :: (a, b) -> () <a href="#v:rnf" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:NFData:NFData:98" class="instance expander" onclick="toggleSection('i:ic:NFData:NFData:98')"></span> (<a href="SafePrelude.html#t:NFData">NFData</a> a, <a href="SafePrelude.html#t:NFData">NFData</a> b) => <a href="SafePrelude.html#t:NFData">NFData</a> (<a href="../array-0.5.1.1/Data-Array.html#t:Array">Array</a> a b)</span></td><td class="doc empty"> </td></tr><tr><td colspan="2"><div id="section.i:ic:NFData:NFData:98" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:rnf">rnf</a> :: <a href="../array-0.5.1.1/Data-Array.html#t:Array">Array</a> a b -> () <a href="#v:rnf" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:NFData:NFData:99" class="instance expander" onclick="toggleSection('i:ic:NFData:NFData:99')"></span> (<a href="SafePrelude.html#t:NFData">NFData</a> a, <a href="SafePrelude.html#t:NFData">NFData</a> b) => <a href="SafePrelude.html#t:NFData">NFData</a> (<a href="../base-4.9.0.0/Data-Semigroup.html#t:Arg">Arg</a> a b)</span></td><td class="doc"><p><em>Since: 1.4.2.0</em></p></td></tr><tr><td colspan="2"><div id="section.i:ic:NFData:NFData:99" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:rnf">rnf</a> :: <a href="../base-4.9.0.0/Data-Semigroup.html#t:Arg">Arg</a> a b -> () <a href="#v:rnf" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:NFData:NFData:100" class="instance expander" onclick="toggleSection('i:ic:NFData:NFData:100')"></span> <a href="SafePrelude.html#t:NFData">NFData</a> (<a href="SafePrelude.html#t:Proxy">Proxy</a> k a)</span></td><td class="doc"><p><em>Since: 1.4.0.0</em></p></td></tr><tr><td colspan="2"><div id="section.i:ic:NFData:NFData:100" class="inst-details hide"><div class="subs methods"><p class="caption">Methods</p><p class="src"><a href="#v:rnf">rnf</a> :: <a href="SafePrelude.html#t:Proxy">Proxy</a> k a -> () <a href="#v:rnf" class="selflink">#</a></p></div></div></td></tr><tr><td class="src clearfix"><span class="inst-left"><span id="control.i:ic:NFData:NFData:101" class="instance expa
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||
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second.</p><p>The name <code><a href="SafePrelude.html#v:deepseq">deepseq</a></code> is used to illustrate the relationship to <code><a href="SafePrelude.html#v:seq">seq</a></code>:
|
||
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where <code><a href="SafePrelude.html#v:seq">seq</a></code> is shallow in the sense that it only evaluates the top
|
||
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level of its argument, <code><a href="SafePrelude.html#v:deepseq">deepseq</a></code> traverses the entire data structure
|
||
|
|
evaluating it completely.</p><p><code><a href="SafePrelude.html#v:deepseq">deepseq</a></code> can be useful for forcing pending exceptions,
|
||
|
|
eradicating space leaks, or forcing lazy I/O to happen. It is
|
||
|
|
also useful in conjunction with parallel Strategies (see the
|
||
|
|
<code>parallel</code> package).</p><p>There is no guarantee about the ordering of evaluation. The
|
||
|
|
implementation may evaluate the components of the structure in
|
||
|
|
any order or in parallel. To impose an actual order on
|
||
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evaluation, use <code>pseq</code> from <a href="Control-Parallel.html">Control.Parallel</a> in the
|
||
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<code>parallel</code> package.</p><p><em>Since: 1.1.0.0</em></p></div></div><div class="top"><p class="src"><a id="v:-36--33--33-" class="def">($!!)</a> :: <a href="SafePrelude.html#t:NFData">NFData</a> a => (a -> b) -> a -> b <span class="fixity">infixr 0</span><span class="rightedge"></span> <a href="#v:-36--33--33-" class="selflink">#</a></p><div class="doc"><p>the deep analogue of <code><a href="SafePrelude.html#v:-36--33-">$!</a></code>. In the expression <code>f $!! x</code>, <code>x</code> is
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||
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fully evaluated before the function <code>f</code> is applied to it.</p><p><em>Since: 1.2.0.0</em></p></div></div><div class="top"><p class="src"><a id="v:force" class="def">force</a> :: <a href="SafePrelude.html#t:NFData">NFData</a> a => a -> a <a href="#v:force" class="selflink">#</a></p><div class="doc"><p>a variant of <code><a href="SafePrelude.html#v:deepseq">deepseq</a></code> that is useful in some circumstances:</p><pre>force x = x `deepseq` x</pre><p><code>force x</code> fully evaluates <code>x</code>, and then returns it. Note that
|
||
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|
<code>force x</code> only performs evaluation when the value of <code>force x</code>
|
||
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itself is demanded, so essentially it turns shallow evaluation into
|
||
|
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deep evaluation.</p><p><code><a href="SafePrelude.html#v:force">force</a></code> can be conveniently used in combination with <code>ViewPatterns</code>:</p><pre>{-# LANGUAGE BangPatterns, ViewPatterns #-}
|
||
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import Control.DeepSeq
|
||
|
|
|
||
|
|
someFun :: ComplexData -> SomeResult
|
||
|
|
someFun (force -> !arg) = {- 'arg' will be fully evaluated -}</pre><p>Another useful application is to combine <code><a href="SafePrelude.html#v:force">force</a></code> with
|
||
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<code><a href="../base-4.9.0.0/Control-Exception.html#v:evaluate">evaluate</a></code> in order to force deep evaluation
|
||
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relative to other <code><a href="SafePrelude.html#t:IO">IO</a></code> operations:</p><pre>import Control.Exception (evaluate)
|
||
|
|
import Control.DeepSeq
|
||
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||
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main = do
|
||
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result <- evaluate $ force $ pureComputation
|
||
|
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{- 'result' will be fully evaluated at this point -}
|
||
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return ()</pre><p><em>Since: 1.2.0.0</em></p></div></div><h2 id="g:25">Monoids</h2><div class="top"><p class="src"><a id="v:-43--43-" class="def">(++)</a> :: <a href="SafePrelude.html#t:Monoid">Monoid</a> m => m -> m -> m <span class="fixity">infixr 5</span><span class="rightedge"></span> <a href="src/SafePrelude.html#%2B%2B" class="link">Source</a> <a href="#v:-43--43-" class="selflink">#</a></p><div class="doc"><p>Operator version of <code><a href="SafePrelude.html#v:mappend">mappend</a></code>.</p><p>In base, this operator is known as <code><a href="SafePrelude.html#v:-60--62-"><></a></code>. However, this is the name
|
||
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|
of the operator for <code><a href="SafePrelude.html#t:Semigroup">Semigroup</a></code> as well. Once <code><a href="SafePrelude.html#t:Semigroup">Semigroup</a></code> is a
|
||
|
|
superclass of <code><a href="SafePrelude.html#t:Monoid">Monoid</a></code>, this historical accident will be
|
||
|
|
unimportant. In the meanwhile, <code>SafePrelude</code> deals with this
|
||
|
|
situation by making <code><a href="SafePrelude.html#v:-60--62-"><></a></code> the <code><a href="SafePrelude.html#t:Semigroup">Semigroup</a></code> operator, and <code><a href="SafePrelude.html#v:-43--43-">++</a></code> the
|
||
|
|
<code><a href="SafePrelude.html#t:Monoid">Monoid</a></code> operator.</p><p><em>Since: 0.1.0.0</em></p></div></div><h2 id="g:26">Read</h2><div class="top"><p class="src"><a id="v:readMaybe" class="def">readMaybe</a> :: <a href="SafePrelude.html#t:Read">Read</a> a => <a href="SafePrelude.html#t:String">String</a> -> <a href="SafePrelude.html#t:Maybe">Maybe</a> a <a href="#v:readMaybe" class="selflink">#</a></p><div class="doc"><p>Parse a string using the <code><a href="SafePrelude.html#t:Read">Read</a></code> instance.
|
||
|
|
Succeeds if there is exactly one valid result.</p><p><em>Since: 4.6.0.0</em></p></div></div><div class="top"><p class="src"><a id="v:readEither" class="def">readEither</a> :: <a href="SafePrelude.html#t:Read">Read</a> a => <a href="SafePrelude.html#t:String">String</a> -> <a href="SafePrelude.html#t:Either">Either</a> <a href="SafePrelude.html#t:String">String</a> a <a href="#v:readEither" class="selflink">#</a></p><div class="doc"><p>Parse a string using the <code><a href="SafePrelude.html#t:Read">Read</a></code> instance.
|
||
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|
Succeeds if there is exactly one valid result.
|
||
|
|
A <code><a href="SafePrelude.html#v:Left">Left</a></code> value indicates a parse error.</p><p><em>Since: 4.6.0.0</em></p></div></div></div></div><div id="footer"><p>Produced by <a href="http://www.haskell.org/haddock/">Haddock</a> version 2.17.2</p></div></body></html>
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