validated-literals-0.3.0: examples/ByteString.hs

{-# OPTIONS_GHC -fno-warn-orphans #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE TemplateHaskell #-}
module ByteString (ByteString) where

import Data.ByteString.Char8 (ByteString, pack)
import qualified Data.ByteString as BS
import Data.Char
import Language.Haskell.TH.Syntax

import ValidLiterals

instance Validate String ByteString where
    fromLiteralWithError s = case nonAsciiVals of
        [] -> Right $ pack s
        _ -> Left $ "Found non-ASCII values: " ++ show nonAsciiVals
      where
        nonAsciiVals = filter (not . (<=255) . ord) s

    liftResult _ v = unsafeTExpCoerce $
        AppE <$> [| BS.pack |] <*> lift (BS.unpack v)