Hallo, For fun and learning I'm trying to parse R5RS Scheme with Parsec. The code to parse lists follows: -- -- Lists -- parseLeftList :: Parser [SchDatum] parseLeftList = do char '(' many parseDatum >>= return . filter (/= SchAtmosphere) parseDottedList :: [SchDatum] -> Parser SchDatum parseDottedList ls = do char '.' many1 parseAtmosphere d <- parseDatum many parseAtmosphere char ')' return $ SchDottedList ls d parseProperList :: [SchDatum] -> Parser SchDatum parseProperList ls = do char ')' return $ SchList ls parseList :: Parser SchDatum parseList = do ls <- parseLeftList (parseDottedList ls) <|> (parseProperList ls) I've factored out the common left sub-expression in parseLeftList. The problem is that "..." is a valid identifier so when inside the left of the list the parser sees a single dot, it tries to match it with "...", which fails. Can anybody give advice on how to rewrite these list parsing functions? Cheers, -- -alex http://www.ventonegro.org/