Stephane Bortzmeyer wrote:
I'm trying to use Parsec for a language which have identifiers where the '-' character is allowed only inside identifiers, not at the start or the end.
identifier = do start <- letter rest <- many (alphaNum <|> char '-') end <- letter return ([start] ++ rest ++ [end]) "characters authorized for identifiers"
identifier = do start <- letter rest <- many (alphaNum <|> try inner_minus) return $ start : rest where inner_minus = do char '-' lookAhead alphaNum return '-'
because the parser created by "many" is greedy: it consumes everything, including the final letter.
Yes, it does. You could implement you own non-greedy many combinator, but you get the associated inefficiency. Or you could use ReadP, which doesn't have this problem (but replaces it with other surprises). Udo. -- Eagles may soar but weasels don't get sucked into jet engines. -- Steven Wright