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Programming language: Haskell
License: BSD 3-clause "New" or "Revised" License
Tags: Data     Interpolatedstring    
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QuasiQuoter for QQ2-style multi-line interpolated strings with "q", "qq" and "qc" support.


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.QQ2 (q)
foo :: String -- Text, ByteString etc also works
foo = [q|

Well here is a
    multi-line string!


Any instance of the IsString class is permitted.

The qc form interpolates curly braces: expressions inside #{} will be directly interpolated if it's a Char, String, Text or ByteString, or it will 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.QQ2 (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:

For example, this instance allows you to display interpolated lists of strings as a sequence of words, removing those pesky brackets, quotes, and escape sequences.

{-# LANGUAGE FlexibleInstances #-}
import Text.InterpolatedString.QQ2 (qc, ShowQ(..))
instance ShowQ [String] where
    showQ = unwords

qc permits output to any types with both IsString and Monoid instances.

{-# LANGUAGE QuasiQuotes, OverloadedStrings #-}
import Text.InterpolatedString.QQ2 (qc)
import Data.Text (Text)
import Data.ByteString.Char8 (ByteString)
qux :: ByteString
qux = [qc| This will convert #{"Text" :: Text} to #{"ByteString" :: ByteString} |]