Stream.hs

{-# LANGUAGE MultiParamTypeClasses, FlexibleInstances, FlexibleContexts #-}
{-# LANGUAGE FunctionalDependencies #-}
{-# LANGUAGE UndecidableInstances #-}     -- Why?

-----------------------------------------------------------------------------
-- |
-- Module      :  Parsimony.Char
-- Copyright   :  (c) Iavor S. Diatchki 2009
-- License     :  BSD3
--
-- Maintainer  :  iavor.diatchki@gmail.com
-- Stability   :  provisional
--
-- A generic way to extract tokens from a stream.
--
-----------------------------------------------------------------------------



module Parsimony.Stream (Token(..), Stream(..)) where

import Parsimony.Prim
import Parsimony.Pos
import Parsimony.Error

import qualified Data.ByteString as Strict (ByteString,uncons)
import qualified Data.ByteString.Lazy as Lazy (ByteString,uncons)
import qualified Data.Text as T
import qualified Data.Text.Lazy as LT
import Data.Word (Word8)
import Numeric (showHex)

-- | A class describing useful token operations.
class Token token where
  -- | How tokens affect file positions.
  updatePos :: token -> SourcePos -> SourcePos

  -- | How to display tokens.
  showToken :: token -> String

instance Token Char where
  updatePos c p = updatePosChar p c
  showToken     = show

instance Token Word8 where
  updatePos _ p = incSourceColumn p 1
  showToken b   = "0x" ++ showHex b ""




-- We have the fun. dep. here because otherwise multiple
-- reads from a stream could give potentially different types of
-- tokens which leads to ambiguities.

-- | Streams of tokens.
class Token token => Stream stream token | stream -> token where
  getToken :: PrimParser stream token

eof_err :: SourcePos -> Reply s a
eof_err p = Error $ newErrorMessage (UnExpect "end of input") p

{-# INLINE genToken #-}
genToken :: Token t => (i -> Maybe (t,i)) -> PrimParser i t
genToken unc (State i p) =
    case unc i of
      Nothing     -> eof_err p
      Just (t,ts) -> Ok t State { stateInput = ts
                                , statePos   = updatePos t p
                                }

instance Token a => Stream [a] a where
  getToken = genToken (\xs -> case xs of
                                [] -> Nothing
                                c : cs -> Just (c,cs))

instance Stream Strict.ByteString Word8 where
  getToken = genToken Strict.uncons

instance Stream Lazy.ByteString Word8 where
  getToken = genToken Lazy.uncons

instance Stream T.Text Char where
  getToken = genToken T.uncons

instance Stream LT.Text Char where
  getToken = genToken LT.uncons