gistfile1.hs

module LangParser(parseGrammar, Token(..)) where

import Control.Applicative
import Control.Monad

data Token =
    Return              |
    Simple Char         |
    OctalConst String   |
    DecimalConst String |
    HexConst String     |
    NamedParam String   |
    Identifier String   |
    LexError String
    deriving (Eq, Show)

tReturn :: [Token] -> Maybe [Token]
tReturn [] = Nothing
tReturn (x:xs) = f x xs
    where f Return xs = Just xs
          f _ _ = Nothing

tSimple :: Char -> [Token] -> Maybe [Token]
tSimple _ [] = Nothing
tSimple c (x:xs) = f x xs
    where f (Simple c) xs = Just xs
          f _ _ = Nothing

parseGrammar :: [Token] -> Maybe [Token]
parseGrammar = retexpr

expr :: [Token] -> Maybe [Token]
expr = tSimple ':'

retexprs :: [Token] -> Maybe [Token]
retexprs = multiexpr <|> expr
    where multiexpr = expr >=> tSimple ',' >=> retexprs

retexpr :: [Token] -> Maybe [Token]
retexpr = tReturn >=> retexprs