Added Turtle.Format

src/Turtle.hs

@@ -8,6 +8,8 @@
 --  This module re-exports the rest of the library and also re-exports useful
 --  modules from @base@:
 --
+--  "Turtle.Format" provides type-safe string formatting
+--
 --  "Turtle.Pattern" provides `Pattern`s, which are like more powerful regular
 --  expressions
 --
@@ -61,7 +63,8 @@
 
 module Turtle (
     -- * Modules
-      module Turtle.Pattern
+      module Turtle.Format
+    , module Turtle.Pattern
     , module Turtle.Protected
     , module Turtle.Shell
     , module Turtle.Prelude
@@ -77,6 +80,7 @@ module Turtle (
     , ExitCode(..)
     ) where
 
+import Turtle.Format
 import Turtle.Pattern
 import Turtle.Protected
 import Turtle.Shell

src/Turtle/Format.hs

@@ -0,0 +1,106 @@
+{-# LANGUAGE OverloadedStrings #-}
+
+{-| Minimalist implementation of type-safe formatted strings, borrowing heavily
+    from the implementation of the @formatting@ package.
+
+    Example use of this module:
+
+>>> :set -XOverloadedStrings
+>>> import Turtle
+>>> format ("This is a "%s%" string that takes "%d%" arguments") "format" 2
+"This is a format string that takes 2 arguments"
+
+    A `Format` string that takes no arguments has this type:
+
+> "I take 0 arguments" :: Format r r
+>
+> format "I take 0 arguments" :: Text
+
+    A `Format` string that takes one argument has this type:
+
+> "I take "%d%" arguments" :: Format r (Int -> r)
+>
+> format ("I take "%d%" argument") :: Int -> Text
+>
+> format ("I take "%d%" argument") 1 :: Text
+
+    A `Format` string that takes two arguments has this type:
+
+> "I "%s%" "%d%" arguments" :: Format r (Text -> Int -> r)
+>
+> format ("I "%s%" "%d%" arguments") :: Text -> Int -> Text
+>
+> format ("I "%s%" "%d%" arguments") "take" 2 :: Text
+-}
+
+{-# LANGUAGE TypeFamilies #-}
+
+module Turtle.Format (
+    -- * Format
+      Format
+    , (%)
+    , format
+    , makeFormat
+
+    -- * Parameters
+    , w
+    , d
+    , u
+    , f
+    , s
+    ) where
+
+import Control.Category (Category(..))
+import Data.Monoid ((<>))
+import Data.String (IsString(..))
+import Data.Text (Text, pack)
+import Data.Word (Word)
+import Prelude hiding ((.), id, FilePath)
+
+-- | A `Format` string
+newtype Format a b = Format { (>>-) :: (Text -> a) -> b }
+
+instance Category Format where
+    id = Format (\return_ -> return_ "")
+
+    fmt1 . fmt2 = Format (\return_ ->
+        fmt1 >>- \str1 ->
+        fmt2 >>- \str2 ->
+        return_ (str1 <> str2) )
+
+-- | Concatenate two `Format` strings
+(%) :: Format b c -> Format a b -> Format a c
+(%) = (.)
+
+instance (a ~ b) => IsString (Format a b) where
+    fromString str = Format (\return_ -> return_ (pack str))
+
+{-| Convert a `Format` string to a print function that takes zero or more typed
+    arguments and returns a `Text` string
+-}
+format :: Format Text r -> r
+format fmt = fmt >>- id
+
+-- | Create your own format specifier
+makeFormat :: (a -> Text) -> Format r (a -> r)
+makeFormat k = Format (\return_ -> \a -> return_ (k a))
+
+-- | `Format` string that inserts any `Show`able value
+w :: Show a => Format r (a -> r)
+w = makeFormat (pack . show)
+
+-- | `Format` string that inserts an `Int` value
+d :: Format r (Int -> r)
+d = w
+
+-- | `Format` string that inserts a `Word` value
+u :: Format r (Word -> r)
+u = w
+
+-- | `Format` string that inserts a `Double`
+f :: Format r (Double -> r)
+f = w
+
+-- | `Format` string that inserts `Text`
+s :: Format r (Text -> r)
+s = makeFormat id

turtle.cabal

@@ -50,6 +50,7 @@ Library
         Build-Depends: unix  >= 2.5.1.0 && < 2.8
     Exposed-Modules:
         Turtle,
+        Turtle.Format,
         Turtle.Pattern,
         Turtle.Protected,
         Turtle.Shell,