{- |

Module : $Header$

Description : Parsec extensions

Copyright : (c) Christian Maeder, DFKI GmbH 2010

License : similar to LGPL, see HetCATS/LICENSE.txt or LIZENZ.txt

Maintainer : Christian.Maeder@dfki.de

Stability : provisional

Portability : portable

frequently useful shortcuts mainly for character parsers

-}

module Common.Parsec where

import Text.ParserCombinators.Parsec

import Control.Monad

-- * monad shortcuts

infixl 1 <<

(<<) :: Monad m => m a -> m b -> m a

(<<) = liftM2 const

forget :: Monad m => m a -> m ()

forget = (>> return ())

pair :: Monad m => m a -> m b -> m (a, b)

pair = liftM2 (,)

infixr 5 <:>

(<:>) :: Monad m => m a -> m [a] -> m [a]

(<:>) = liftM2 (:)

infixr 5 <++>

(<++>) :: Monad m => m [a] -> m [a] -> m [a]

(<++>) = liftM2 (++)

single :: Monad m => m a -> m [a]

single = liftM return

flat :: Monad m => m [[a]] -> m [a]

flat = liftM concat

enclosedBy :: Monad m => m [a] -> m a -> m [a]

enclosedBy p q = q <:> p <++> single q

-- * parsec shortcuts

-- | parse an optional list

optionL :: GenParser tok st [a] -> GenParser tok st [a]

optionL = option []

-- | shortcut for @try . string@

tryString :: String -> CharParser st String

tryString = try . string

-- | nested comments, open and closing strings must have at least two chars

nestedComment :: String -> String -> CharParser st String

nestedComment op cl = case (op, cl) of

(oh : ot : _, ch : ct : _) ->

tryString op <++>

flat (many $ single

(noneOf [oh, ch]

<|> try (char ch << notFollowedBy (char ct))

<|> try (char oh << notFollowedBy (char ot)))

<|> nestedComment op cl)

<++> string cl

_ -> error "nestedComment"

-- | non-nested block

plainBlock :: String -> String -> CharParser st String

plainBlock op cl = tryString op >> manyTill anyChar (tryString cl)

reserved :: [String] -> CharParser st String -> CharParser st String

-- | reject keywords

reserved l p = try $ do

s <- p

if elem s l then unexpected $ show s else return s