Parse.hs

simpleParse :: ParseState -> (a, ParseState)
simpleParse = undefined

betterParse :: ParseState -> Either String (a, ParseState)
betterParse = undefined

newtype Parse a = Parse {
  runParse :: ParseState -> Either String (a, ParseState)
}

identity :: a -> Parse a
identity a = Parse (\s -> Right (a, s))

parse :: Parse a -> L.ByteString -> Either String a
parse parser initState
  = case runParse parser (ParseState initState 0) of
      Left err          -> Left err
      Right (result, _) -> Right result