Am Montag, 10. Dezember 2007 14:45 schrieb Ryan Bloor:

hi I am writing a basic Parser from scratch. So far I have functions;# removeSpaces# match - which checks if a string is a substring of another# orParser which combines two parser's abilities# Basic pasrers like... parseInt, parseTrue, parseFalse, parseBoolusing the orParser on True and False.What I want to do now is have a parseBinaryOp that recognises:parseBinaryOp "+" "(5 + 2) if" >>>gives>> [(EInt 5, EInt 2, "if")]So I think that I have to split the initial string into four parts."+" becomes op'(' becomes tokenF')' becomes tokenB"5" becomes e1"2" becomes e2parseBinaryOp :: String -> String -> [(Expr, Expr, String)]parseBinaryOp op str = let (tokenF,e1,op,e2,tokenB) =I am not sure how to go about separating the string for how I need itusing my other functiuons. Ryan

Keep it simpler. Write combinators parseFirstThen :: Parser a -> Parser b -> Parser (a,b) parseFirstThenWith :: (a -> b -> c) -> Parser a -> Parser b -> Parser c or applyToParse :: (a -> b) -> Parser a -> Parser b (then you would find parseFirstThenWith f p1 p2 === applyToParse (uncurry f) (parseFirstThen p1 p2) and applyToParse f p === parseFirstThenWith (const . f) p (succeed ()) where succeed x input = [(x,input)] ) and compose your parser using these. Better still, read http://www.haskell.org/haskellwiki/Homework_help and the chapter on parsing in any tutorial/textbook, docs and sources for parsing libraries, such as parsec.