textural/src/Data/Text/IsText.hs

{-# LANGUAGE TypeSynonymInstances #-}
{-# LANGUAGE FlexibleInstances #-}

module Data.Text.IsText where

import Data.String
import qualified Data.ByteString as SB
import qualified Data.ByteString.Lazy as LB
import qualified Codec.Binary.UTF8.String as UTF8
import qualified Data.Text as T

{- | Type class for data structures that are logically text -}
class IsString a => IsText a where
  toString :: a -> String

instance IsText String where
  toString = id
{- | The UTF-8 encoding is assumed for ByteStrings -}
instance IsText SB.ByteString where
  toString = UTF8.decode . SB.unpack
{- | The UTF-8 encoding is assumed for ByteStrings -}
instance IsText LB.ByteString where
  toString = UTF8.decode . LB.unpack
instance IsText T.Text where
  toString = T.unpack

{- | Converts between instances of IsText -}
fromText :: (IsText a, IsText b) => a -> b
fromText = fromString . toString