    {- arch-tag: Parsec utilities
    Copyright (C) 2004 John Goerzen <jgoerzen@complete.org>

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program; if not, write to the Free Software
    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
    -}

    {- |
       Module     : Text.ParserCombinators.Parsec.Utils
       Copyright  : Copyright (C) 2004 John Goerzen
       License    : GNU GPL, version 2 or above

       Maintainer : John Goerzen <jgoerzen@complete.org>
       Stability  : provisional
       Portability: portable

    Written by John Goerzen, jgoerzen\@complete.org

    -}

    module Text.ParserCombinators.Parsec.Utils(-- * Generalized Utilities
                           -- | These functions are generalized versions of
                           -- ones you might see in the Char parser.
                           GeneralizedToken, GeneralizedTokenParser,
                           togtok, tokeng, satisfyg, oneOfg, noneOfg,
                           specificg, allg,
                           -- * Other Utilities
                           notMatching
                          ) where

    import Text.ParserCombinators.Parsec

    type GeneralizedToken a = (SourcePos, a)
    type GeneralizedTokenParser a st b = GenParser (GeneralizedToken a) st b

    {- | Generate (return) a 'GeneralizedToken'. -}
    togtok :: a -> GenParser b st (GeneralizedToken a)
    togtok tok = do
                  x <- getPosition
                  return (x, tok)

    {- | Retrieve the next token from a 'GeneralizedToken' stream.
       The given function should return the value to use, or Nothing
       to cause an error. -}
    tokeng :: (Show a) => (a -> Maybe b) -> GeneralizedTokenParser a st b
    tokeng test =
        token (show . snd) (fst) (test . snd)

    {- | A shortcut to 'tokeng'; the test here is just a function that returns
    a Bool.  If the result is true; return that value -- otherwise, an error.
    -}
    satisfyg :: (Show a) => (a -> Bool) -> GeneralizedTokenParser a st a
    satisfyg test = tokeng (\t -> if test t then Just t else Nothing)

    {- | Matches one item in a list and returns it. -}
    oneOfg :: (Eq a, Show a) => [a] -> GeneralizedTokenParser a st a
    oneOfg i = satisfyg (\x -> elem x i)

    {- | Matches all items and returns them -}
    allg :: (Show a) => GeneralizedTokenParser a st [a]
    allg = many $ satisfyg (\_ -> True)

    {- | Matches one item not in a list and returns it. -}
    noneOfg :: (Eq a, Show a) => [a] -> GeneralizedTokenParser a st a
    noneOfg l = satisfyg (\x -> not (elem x l))

    {- | Matches one specific token and returns it. -}
    specificg :: (Eq a, Show a) => a -> GeneralizedTokenParser a st a
    specificg i = satisfyg (== i) <?> show i

    {- Matches a list of tokens and returns it. -}
    {-
    listg :: (Eq a, Show a) => [GeneralizedToken a] -> GeneralizedTokenParser a st [GeneralizedToken a]
    listg l = tokens (show . map fst) nextpos l
              where
              tokpos = fst
              nextpos
              nextposs _ _ (tok:toks) = tokpos tok
              nextposs _ tok [] = tokpos tok
              nextpos pos x = nextposs pos [x]
    -}

    {- | Running @notMatching p msg@ will try to apply parser p.
    If it fails, returns ().  If it succeds, cause a failure and raise
    the given error message.  It will not consume input in either case. -}
    notMatching :: GenParser a b c -> String -> GenParser a b ()
    notMatching p errormsg =
        let maybeRead = try (do
                             x <- p
                             return (Just x)
                            )
                        <|> return Nothing
            workerFunc =  do
                          x <- maybeRead
                          case x of
                                 Nothing -> return ()
                                 Just _ -> unexpected errormsg
            in
            try workerFunc