HaskellParser

From TKwiki

import Char
 
type Parser a = String -> Maybe (a, String)
 
parseInt :: Parser Int
parseInt [] = Nothing
parseInt (x:xs)
		| isNumeric x = let (cislo, zbytek) = (parseInt' (x:xs) 0) in Just ( cislo , zbytek ) 
		| otherwise = Nothing
		where
			parseInt' :: String -> Int -> ( Int , String )
			parseInt' [] a = ( a, [] )
			parseInt' (x:xs) a
				| toNum x == Nothing = (a, (x:xs) )
				| otherwise = let Just y = toNum x in parseInt' xs ((a*10)+y)
			toNum :: Char -> Maybe Int
			toNum x
				| isNumeric x = Just ( ord(x) - ord('0') )
				| otherwise = Nothing
			isNumeric :: Char -> Bool
			isNumeric x
				| ((ord(x)>=ord('0')) && ( ord(x)<=ord('9') )) = True
				| otherwise = False