371 lines
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371 lines
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<section class="slide">
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<div style="text-align:center; position:absolute; top: 2em; font-size: .9em; width: 100%">
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<h1 style="position: relative;">Parsec</h1>
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<author><em class="base01">by</em> Yann Esposito</author>
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<div style="font-size:.5em">
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<twitter>
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<a href="http://twitter.com/yogsototh">@yogsototh</a>,
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<a href="https://plus.google.com/117858550730178181663">+yogsototh</a>
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HTML presentation: use arrows, space to navigate.
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</div>
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</div>
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</section>
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<section class="slide">
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<h2 id="parsing">Parsing</h2>
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<p>Latin pars (ōrātiōnis), meaning part (of speech).</p>
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<ul>
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<li><strong>analysing a string of symbols</strong></li>
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<li><strong>formal grammar</strong>.</li>
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</ul>
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</section>
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<section class="slide">
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<h2 id="parsing-in-programming-languages">Parsing in Programming Languages</h2>
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<p>Complexity:</p>
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<table>
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<thead>
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<tr class="header">
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<th align="left">Method</th>
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<th align="left">Typical Example</th>
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<th align="left">Output Data Structure</th>
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</tr>
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</thead>
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<tbody>
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<tr class="odd">
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<td align="left">Splitting</td>
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<td align="left">CSV</td>
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<td align="left">Array, Map</td>
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</tr>
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<tr class="even">
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<td align="left">Regexp</td>
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<td align="left">email</td>
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<td align="left">+ Fixed Layout Tree</td>
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</tr>
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<tr class="odd">
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<td align="left">Parser</td>
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<td align="left">Programming language</td>
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<td align="left">+ Most Data Structure</td>
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</tr>
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</tbody>
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</table>
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</section>
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<section class="slide">
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<h2 id="parser-culture">Parser <span class="and">&</span> culture</h2>
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<p>In Haskell Parser are really easy to use.</p>
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<p>Generally:</p>
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<ul>
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<li>In most languages: <strong>split</strong> then <strong>regexp</strong> then <strong>parse</strong></li>
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<li>In Haskell: <strong>split</strong> then <strong>parse</strong></li>
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</ul>
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</section>
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<section class="slide">
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<h2 id="parsing-example">Parsing Example</h2>
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<p>From String:</p>
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<pre class="sourceCode haskell"><code class="sourceCode haskell">(<span class="dv">1</span><span class="fu">+</span><span class="dv">3</span>)<span class="fu">*</span>(<span class="dv">1</span><span class="fu">+</span><span class="dv">5</span><span class="fu">+</span><span class="dv">9</span>)</code></pre>
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<p>To data structure:</p>
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<p><img src="parsec/img/mp/AST.png" alt="AST" /><br /></p>
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</section>
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<section class="slide">
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<h2 id="parsec">Parsec</h2>
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<blockquote>
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<p>Parsec lets you construct parsers by combining high-order Combinators to create larger expressions.</p>
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<p>Combinator parsers are written and used within the same programming language as the rest of the program.</p>
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<p>The parsers are first-class citizens of the languages [...]"</p>
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</blockquote>
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</section>
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<section class="slide">
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<h2 id="parser-libraries">Parser Libraries</h2>
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<p>In reality there are many choices:</p>
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<table>
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<tbody>
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<tr class="odd">
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<td align="left">attoparsec</td>
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<td align="left">fast</td>
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</tr>
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<tr class="even">
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<td align="left">Bytestring-lexing</td>
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<td align="left">fast</td>
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</tr>
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<tr class="odd">
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<td align="left">Parsec 3</td>
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<td align="left">powerful, nice error reporting</td>
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</tr>
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</tbody>
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</table>
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</section>
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<section class="slide">
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<h2 id="haskell-remarks-1">Haskell Remarks (1)</h2>
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<p>spaces are meaningful</p>
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<pre class="sourceCode haskell"><code class="sourceCode haskell">f x <span class="co">-- ⇔ f(x) in C-like languages</span>
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f x y <span class="co">-- ⇔ f(x,y)</span></code></pre>
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</section>
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<section class="slide">
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<h2 id="haskell-remarks-2">Haskell Remarks (2)</h2>
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<p>Don't mind strange operators (<code><*></code>, <code><$></code>).<br />Consider them like separators, typically commas.<br />They are just here to deal with types.</p>
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<p>Informally:</p>
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<pre class="sourceCode haskell"><code class="sourceCode haskell">toto <span class="fu"><$></span> x <span class="fu"><*></span> y <span class="fu"><*></span> z
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<span class="co">-- ⇔ toto x y z</span>
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<span class="co">-- ⇔ toto(x,y,z) in C-like languages</span></code></pre>
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</section>
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<section class="slide">
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<h2 id="a-parsec-example">A Parsec Example</h2>
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<pre class="sourceCode haskell"><code class="sourceCode haskell">whitespaces <span class="fu">=</span> many (oneOf <span class="st">"\t "</span>)
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number <span class="fu">=</span> many1 digit
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symbol <span class="fu">=</span> oneOf <span class="st">"!#$%<span class="and">&</span>|*+-/:<=>?@^_~"</span></code></pre>
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<pre class="sourceCode haskell"><code class="sourceCode haskell"><span class="st">" \t "</span> <span class="co">-- whitespaces on " \t "</span>
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<span class="st">""</span> <span class="co">-- whitespaces on "32"</span>
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<span class="st">"32"</span> <span class="co">-- number on "32"</span>
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<span class="co">-- number on " \t 32 "</span>
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<span class="st">"number"</span> (line <span class="dv">1</span>, column <span class="dv">1</span>)<span class="fu">:</span>
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unexpected <span class="st">" "</span>
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expecting digit</code></pre>
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</section>
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<section class="slide">
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<h2 id="comparison-with-regexp-parsec">Comparison with Regexp (Parsec)</h2>
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<pre class="sourceCode haskell"><code class="sourceCode haskell"><span class="kw">data</span> <span class="dt">IP</span> <span class="fu">=</span> <span class="dt">IP</span> <span class="dt">Word8</span> <span class="dt">Word8</span> <span class="dt">Word8</span> <span class="dt">Word8</span>
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ip <span class="fu">=</span> <span class="dt">IP</span> <span class="fu"><$></span>
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number <span class="fu"><*</span> char <span class="ch">'.'</span> <span class="fu"><*></span>
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number <span class="fu"><*</span> char <span class="ch">'.'</span> <span class="fu"><*></span>
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number <span class="fu"><*</span> char <span class="ch">'.'</span> <span class="fu"><*></span>
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number
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number <span class="fu">=</span> <span class="kw">do</span>
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x <span class="ot"><-</span> read <span class="fu"><$></span> many1 digit
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guard (<span class="dv">0</span> <span class="fu"><=</span> x <span class="fu"><span class="and">&</span><span class="and">&</span></span> x <span class="fu"><</span> <span class="dv">256</span>)
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return (fromIntegral x)</code></pre>
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</section>
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<section class="slide">
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<h2 id="comparison-with-regexp-perl-regexp">Comparison with Regexp (Perl Regexp)</h2>
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<pre class="sourceCode perl"><code class="sourceCode perl"><span class="co"># remark: 888.999.999.999 is accepted</span>
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\b\d{<span class="dv">1</span>,<span class="dv">3</span>}\.\d{<span class="dv">1</span>,<span class="dv">3</span>}\.\d{<span class="dv">1</span>,<span class="dv">3</span>}\.\d{<span class="dv">1</span>,<span class="dv">3</span>}\b
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<span class="co"># exact but difficult to read</span>
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\b(?:(?:<span class="dv">25</span>[<span class="dv">0-5</span>]|<span class="dv">2</span>[<span class="dv">0-4</span>][<span class="dv">0-9</span>]|[<span class="dv">01</span>]?[<span class="dv">0-9</span>][<span class="dv">0-9</span>]?)\.){<span class="dv">3</span>}
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(?:<span class="dv">25</span>[<span class="dv">0-5</span>]|<span class="dv">2</span>[<span class="dv">0-4</span>][<span class="dv">0-9</span>]|[<span class="dv">01</span>]?[<span class="dv">0-9</span>][<span class="dv">0-9</span>]?)\b</code></pre>
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<p>Also, regexp are <em>unityped</em> by nature.</p>
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</section>
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<section class="slide">
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<h2 id="monadic-style">Monadic style</h2>
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<pre class="sourceCode haskell"><code class="sourceCode haskell"><span class="ot">number ::</span> <span class="dt">Parser</span> <span class="dt">String</span>
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number <span class="fu">=</span> many1 digit
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<span class="ot">number' ::</span> <span class="dt">Parser</span> <span class="dt">Int</span>
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number' <span class="fu">=</span> <span class="kw">do</span>
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<span class="co">-- digitString :: String</span>
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digitString <span class="ot"><-</span> many1 digit
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return (read digitString)</code></pre>
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<pre class="sourceCode haskell"><code class="sourceCode haskell"><span class="st">"32"</span><span class="ot"> ::</span> [<span class="dt">Char</span>] <span class="co">-- number on "32"</span>
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<span class="dv">32</span><span class="ot"> ::</span> <span class="dt">Int</span> <span class="co">-- number' on "32"</span></code></pre>
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</section>
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<section class="slide">
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<h2 id="combining-monadic-style-s-asb-ε">Combining Monadic style (S = aSb | ε)</h2>
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<pre class="sourceCode haskell"><code class="sourceCode haskell">s <span class="fu">=</span> (<span class="kw">do</span>
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a <span class="ot"><-</span> string <span class="st">"a"</span>
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mid <span class="ot"><-</span> s
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b <span class="ot"><-</span> string <span class="st">"b"</span>
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return (a <span class="fu">++</span> mid <span class="fu">++</span> b)
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<span class="fu"><|></span> string <span class="st">""</span></code></pre>
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<pre class="sourceCode haskell"><code class="sourceCode haskell"><span class="st">""</span> <span class="co">-- s on ""</span>
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<span class="st">"aaabbb"</span> <span class="co">-- s on "aaabbb"</span>
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<span class="st">"aabb"</span> <span class="co">-- s on "aabbb"</span>
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<span class="co">-- s on "aaabb"</span>
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<span class="dt">S</span> (line1 <span class="dv">1</span>, column <span class="dv">4</span>)<span class="fu">:</span>
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unexpected end <span class="kw">of</span> input
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expecting <span class="st">"b"</span></code></pre>
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</section>
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<section class="slide">
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<h2 id="combining-applicative-style-s-asb-ε">Combining Applicative style (S = aSb | ε)</h2>
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<pre class="sourceCode haskell"><code class="sourceCode haskell">s <span class="fu">=</span> concat3 <span class="fu"><$></span> string <span class="st">"a"</span> <span class="fu"><*></span> s <span class="fu"><*></span> char <span class="st">"b"</span>
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<span class="fu"><|></span> string <span class="st">""</span>
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<span class="kw">where</span>
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concat3 x y z <span class="fu">=</span> x <span class="fu">++</span> y <span class="fu">++</span> z</code></pre>
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</section>
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<section class="slide">
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<h2 id="applicative-style-usefull-with-data-types">Applicative Style usefull with Data types</h2>
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<pre class="sourceCode haskell"><code class="sourceCode haskell"><span class="kw">data</span> <span class="dt">IP</span> <span class="fu">=</span> <span class="dt">IP</span> <span class="dt">Int</span> <span class="dt">Int</span> <span class="dt">Int</span> <span class="dt">Int</span>
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parseIP <span class="fu">=</span> <span class="dt">IP</span> <span class="fu"><$></span>
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number <span class="fu"><*</span> char <span class="ch">'.'</span> <span class="fu"><*></span>
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number <span class="fu"><*</span> char <span class="ch">'.'</span> <span class="fu"><*></span>
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number <span class="fu"><*</span> char <span class="ch">'.'</span> <span class="fu"><*></span>
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number
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monadicParseIP <span class="fu">=</span> <span class="kw">do</span>
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d1 <span class="ot"><-</span> number
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char <span class="ch">'.'</span>
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d2 <span class="ot"><-</span> number
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char <span class="ch">'.'</span>
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d3 <span class="ot"><-</span> number
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char <span class="ch">'.'</span>
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d4 <span class="ot"><-</span> number
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return (<span class="dt">IP</span> d1 d2 d3 d4)</code></pre>
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</section>
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<section class="slide">
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<h2 id="write-number-correctly">Write number correctly</h2>
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<pre class="sourceCode haskell"><code class="sourceCode haskell"><span class="ot">number ::</span> <span class="dt">Parser</span> <span class="dt">Int</span>
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number <span class="fu">=</span> <span class="kw">do</span>
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x <span class="ot"><-</span> read <span class="fu"><$></span> many1 digit
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guard (<span class="dv">0</span> <span class="fu"><=</span> x <span class="fu"><span class="and">&</span><span class="and">&</span></span> x <span class="fu"><</span> <span class="dv">256</span>) <span class="fu"><?></span>
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<span class="st">"Number between 0 and 255 (here "</span> <span class="fu">++</span> show x <span class="fu">++</span> <span class="st">")"</span>
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return (fromIntegral x)</code></pre>
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<pre class="sourceCode haskell"><code class="sourceCode haskell"><span class="fu">>>></span> test parseIP <span class="st">"parseIP"</span> <span class="st">"823.32.80.113"</span>
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<span class="st">"parseIP"</span> (line <span class="dv">1</span>, column <span class="dv">4</span>)<span class="fu">:</span>
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unexpected <span class="st">"."</span>
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expecting digit or <span class="dt">Number</span> between <span class="dv">0</span> and <span class="dv">255</span> (here <span class="dv">823</span>)</code></pre>
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</section>
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<section class="slide">
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<h2 id="so">So</h2>
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<ul>
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<li>combination of simple parsers</li>
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<li>error messages with <code>(<?>)</code></li>
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<li>embed result in data type using Applicative style</li>
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<li>Not shown, use another monad with the parser</li>
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</ul>
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<p>Time to do something cool</p>
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</section>
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<section class="slide">
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<h2 id="a-simple-dsl">A Simple DSL</h2>
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<p>Let's write a minimal DSL</p>
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</section>
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<section class="slide">
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<h2 id="useful-definitions">Useful definitions</h2>
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<p><code>try</code> tries to parse and backtracks if it fails.</p>
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<pre class="sourceCode haskell"><code class="sourceCode haskell">(<span class="fu"><||></span>) parser1 parser2 <span class="fu">=</span> try parser1 <span class="fu"><|></span> parser2</code></pre>
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<p><code>lexeme</code>, just skip spaces.</p>
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<pre class="sourceCode haskell"><code class="sourceCode haskell">lexeme parser <span class="fu">=</span> whitespaces <span class="fu">*></span> parser <span class="fu"><*</span> whitespaces</code></pre>
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</section>
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<section class="slide">
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<h2 id="data-structure">Data Structure</h2>
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<p>Remember from text to data structure</p>
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<pre class="sourceCode haskell"><code class="sourceCode haskell"><span class="kw">data</span> <span class="dt">Tree</span> <span class="fu">=</span> <span class="dt">Node</span> <span class="dt">Element</span> [<span class="dt">Tree</span>]</code></pre>
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</section>
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<input type="text" name="slidenum" id="goto-slide" list="goto-datalist">
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<datalist id="goto-datalist"></datalist>
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<input type="submit" value="Go">
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|
</form>
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|
|
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<!-- deck.hash snippet -->
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|
<a href="." title="Permalink to this slide" class="deck-permalink">#</a>
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|
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|
<!-- End extension snippets. -->
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|
|
|
|
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<!-- Required JS files. -->
|
|
<script src="jquery-1.7.2.min.js"></script>
|
|
<script src="core/deck.core.js"></script>
|
|
|
|
<!-- Extension JS files. Add or remove as needed. -->
|
|
<script src="core/deck.core.js"></script>
|
|
<script src="extensions/hash/deck.hash.js"></script>
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|
<script src="extensions/menu/deck.menu.js"></script>
|
|
<script src="extensions/goto/deck.goto.js"></script>
|
|
<script src="extensions/status/deck.status.js"></script>
|
|
<script src="extensions/navigation/deck.navigation.js"></script>
|
|
<!-- <script src="extensions/scale/deck.scale.js"></script> -->
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|
|
|
<!-- Initialize the deck. You can put this in an external file if desired. -->
|
|
<script>
|
|
$(function() {
|
|
$.deck('.slide');
|
|
});
|
|
</script>
|
|
<!-- Y theme -->
|
|
<script src="js/mathjax/MathJax.js?config=TeX-AMS-MML_HTMLorMML"></script>
|
|
<script src="js/highlight/highlight.pack.js"></script>
|
|
<script>
|
|
hljs.initHighlightingOnLoad();
|
|
</script>
|
|
</body>
|
|
</html>
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