Parse.hs

{-# LANGUAGE FlexibleContexts, FunctionalDependencies, MultiParamTypeClasses #-}
-----------------------------------------------------------------------------
-- Copyright 2019, Advise-Me project team. This file is distributed under 
-- the terms of the Apache License 2.0. For more information, see the files
-- "LICENSE.txt" and "NOTICE.txt", which are included in the distribution.
-----------------------------------------------------------------------------
-- |
-- Maintainer  :  bastiaan.heeren@ou.nl
-- Stability   :  provisional
-- Portability :  portable (depends on ghc)
--
-- This module defines the parser interface. It consists of three type classes: ParseState, Parse and ParseLog.
-- These three type classes expose the parsing primitives necessary to be implemented by any parser.
-- Although both ParseState and ParseLog are optional, Parse is not.
-- 
-----------------------------------------------------------------------------

module Recognize.Parsing.Parse where

import Control.Applicative (Alternative, (<|>))
import Control.Monad.State
import Control.Monad.Identity

infixl 3 |>

-- | Interface for the basic parsing primitives
class (Monad m, Alternative m) => Parse m s | m -> s where
  (|>) :: m a -> m a -> m a
  satisfyWith :: (s -> Maybe a) -> m a
  withInputList :: ([s] -> [a]) -> m a
  
  -- input :: m s [s]
  -- lookAhead :: m s a -> m s a

safePeek :: Parse m s => m (Maybe s)
safePeek = withInputList $ \xs -> 
   case xs of
      []   -> [Nothing]
      hd:_ -> [Just hd]
  
option :: Parse m s => m a -> m (Maybe a)
option m = Just <$> m <|> return Nothing

satisfy :: Parse m s => (s -> Bool) -> m s
satisfy f = satisfyWith (\s -> if f s then Just s else Nothing)

guardBy :: (MonadState st m, Alternative m) => (st -> Bool) -> m ()
guardBy p = gets p >>= guard

-- | Interface for monads that are capable of logging.
--
class ParseLog m where
  pLog :: String -> m ()

instance ParseLog Identity where
   pLog _ = return ()

instance ParseLog IO where
   pLog = putStrLn