On Fri, 19 Nov 2004 14:28:07 +0000 (UTC), John Goerzen
Hi,
I'm porting a parser over from an OCamllex/Ocamlyacc version and I'm using Parsec for both the tokenizer and the resulting token stream parser.
I have both of them working fine, but now my question is: how do I combine them? I can't quite figure out how to say "take the output from this GenParser Char () Tok and use it as the input for this GenParser Tok () ParserOutput".
Well, I have figured out an ugly way involving manually starting up both parsers, but it makes position calculations very complex.
Did you try to pair tokens with their SourcePos'es? What I did in my program was this: tokenize :: CharParser st tok -> CharParser st [(SourcePos, tok)] tokenize tp = do l <- many t eof return l where t = do pos <- getPosition tok <- tp return (pos, tok) token :: (Show tok) => (tok -> Maybe a) -> GenParser (SourcePos, tok) st a token f = Parsec.token (show . snd) fst (f . snd) This has a space leak, but I didn't care, because my inputs are at most 10kb long. You can do a lazy version with getInput. BTW, it would be useful if Parsec allowed to throw a ParseError from one type of parser in another parser. It would help me in a situation, where I parse the whole file with one parser, but I retokenize some parts of it and parse them with another parser type. Right now I am using this workaround, but it doesn't work well: cs <- chars pos <- getPosition x <- case p pos cs of Left err -> do setPosition (errorPos err) fail (messageString (head (errorMessages err))) Right x -> return x How about making an instance for instance Control.Monad.Error.MonadError ParseError (GenParser tok st) PS. I guess I could do this myself. Best regards, Tomasz