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{-# LANGUAGE TypeSynonymInstances, FlexibleInstances #-}
-- | /WARNING/: This module is /not/ intended for use outside the TagSoup library.
--
-- This module provides an abstraction for String's as used inside TagSoup. It allows
-- TagSoup to work with String (list of Char), ByteString.Char8, ByteString.Lazy.Char8,
-- Data.Text and Data.Text.Lazy.
module Text.StringLike where
import Data.Typeable
import qualified Data.ByteString.Char8 as BS
import qualified Data.ByteString.Lazy.Char8 as LBS
import qualified Data.Text as T
import qualified Data.Text.Lazy as LT
-- | A class to generalise TagSoup parsing over many types of string-like types.
-- Examples are given for the String type.
class (Typeable a, Eq a) => StringLike a where
-- | > empty = ""
empty :: a
-- | > cons = (:)
cons :: Char -> a -> a
-- | > uncons [] = Nothing
-- > uncons (x:xs) = Just (x, xs)
uncons :: a -> Maybe (Char, a)
-- | > toString = id
toString :: a -> String
-- | > fromString = id
fromString :: String -> a
-- | > fromChar = return
fromChar :: Char -> a
-- | > strConcat = concat
strConcat :: [a] -> a
-- | > strNull = null
strNull :: a -> Bool
-- | > append = (++)
append :: a -> a -> a
-- | Convert a String from one type to another.
castString :: (StringLike a, StringLike b) => a -> b
castString = fromString . toString
instance StringLike String where
uncons [] = Nothing
uncons (x:xs) = Just (x, xs)
toString = id
fromString = id
fromChar = (:[])
strConcat = concat
empty = []
strNull = null
cons c = (c:)
append = (++)
instance StringLike BS.ByteString where
uncons = BS.uncons
toString = BS.unpack
fromString = BS.pack
fromChar = BS.singleton
strConcat = BS.concat
empty = BS.empty
strNull = BS.null
cons = BS.cons
append = BS.append
instance StringLike LBS.ByteString where
uncons = LBS.uncons
toString = LBS.unpack
fromString = LBS.pack
fromChar = LBS.singleton
strConcat = LBS.concat
empty = LBS.empty
strNull = LBS.null
cons = LBS.cons
append = LBS.append
instance StringLike T.Text where
uncons = T.uncons
toString = T.unpack
fromString = T.pack
fromChar = T.singleton
strConcat = T.concat
empty = T.empty
strNull = T.null
cons = T.cons
append = T.append
instance StringLike LT.Text where
uncons = LT.uncons
toString = LT.unpack
fromString = LT.pack
fromChar = LT.singleton
strConcat = LT.concat
empty = LT.empty
strNull = LT.null
cons = LT.cons
append = LT.append
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