interpolatedstring-perl6-0.5: QuasiQuoter for Perl6-style multi-line interpolated strings



QuasiQuoter for interpolated strings using Perl 6 syntax.

The q form does one thing and does it well: It contains a multi-line string with no interpolation at all:

 {-# LANGUAGE QuasiQuotes, ExtendedDefaultRules #-}
 import Text.InterpolatedString.Perl6 (q)
 foo :: String
 foo = [$q|

Well here is a
     multi-line string!


The qc form interpolates curly braces: Expressions inside {} will be directly interpolated if it's a String, or have show called if it is not.

Escaping of '{' is done with backslash.

For interpolating numeric expressions without an explicit type signature, use the ExtendedDefaultRules lanuage pragma, as shown below:

 {-# LANGUAGE QuasiQuotes, ExtendedDefaultRules #-}
 import Text.InterpolatedString.Perl6 (qc)
 bar :: String
 bar = [$qc| Well {"hello" ++ " there"} {6 * 7} |]

bar will have the value " Well hello there 42 ".

If you want control over how show works on your types, define a custom ShowQ instance:

 import Text.InterpolatedString.Perl6 (qc, ShowQ(..))
 instance ShowQ ByteString where
     showQ = unpack

That way you interpolate bytestrings will not result in double quotes or character escapes.

The qq form adds to the qc form with a simple shorthand: '$foo' means '{foo}', namely interpolating a single variable into the string.

 {-# LANGUAGE QuasiQuotes, ExtendedDefaultRules #-}
 import Text.InterpolatedString.Perl6 (qq)
 baz :: String
 baz = [$qc| Hello, $who |]
     who = World

The ability to define custom ShowQ instances is particularly powerful with cascading instances using qq.

Below is a sample snippet from a script that converts Shape objects into AppleScript suitable for drawing in OmniGraffle:

 {-# LANGUAGE QuasiQuotes, ExtendedDefaultRules, NamedFieldPuns, RecordWildCards #-}
 import qualified System.IO.UTF8 as UTF8
 import Text.InterpolatedString.Perl6
 data Shape = Shape
     { originX         :: Int
     , originY         :: Int
     , width           :: Int
     , height          :: Int
     , stroke          :: Stroke
     , text            :: Text
 instance ShowQ Shape where
     showQ Shape{..} = [$qq|
         make new shape at end of graphics with properties
             \{ $text, $stroke, _size, $_origin }
         _size   = [$qq|size: {$width, $height}|]
         _origin = [$qq|origin: {$originX, $originY}|]
 data Stroke = StrokeWhite | StrokeNone
 instance ShowQ Stroke where
     showQ StrokeNone = "draws stroke:false"
     showQ StrokeWhite = "stroke color: {1, 1, 1}"
 data Text   = Text
     { txt   :: String
     , color :: Color
 instance ShowQ Text where
     showQ Text{..} = [$qq|text: \{ text: "$txt", $color, alignment: center } |]
 data Color = Color { red :: Float, green :: Float, blue :: Float }
 instance ShowQ Color where
     showQ Color{..} = [$qq|color: {$red, $green, $blue}|]
 main :: IO ()
 main = UTF8.putStrLn [$qq|
     tell application "OmniGraffle Professional 5"
         tell canvas of front window
             { makeShape ... }
         end tell
     end tell



qq :: QuasiQuoterSource

QuasiQuoter for interpolating '$var' and '{expr}' into a string literal. The pattern portion is undefined.

qc :: QuasiQuoterSource

QuasiQuoter for interpolating '{expr}' into a string literal. The pattern portion is undefined.

q :: QuasiQuoterSource

QuasiQuoter for a non-interpolating string literal. The pattern portion is undefined.

class ShowQ a whereSource


showQ :: a -> StringSource