Re: [Haskell-cafe] Parsec question

Jason Dusek wrote:

2009/04/17 minh thu :

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2009/04/17 Michael Mossey :

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I wonder how I can get the manyTill to be happy with eof before finding the //? I tried

parseText = manyTill anyChar (try (string "//") <|> eof)

but got a type error. You can use 'notFollowedBy' [...]

You get a type error because `string "//"` parses to a `String` while `eof` parses to a `()`. Instead you might use:

parseText = manyTill anyChar (try (string "//" >> return ()) <|> eof)

-- Jason Dusek

Ah.. I think I get it... in the function manyTill, the second argument type doesn't matter.. doesn't have to match the first argument type. Here's what I have so far. It works, but it's a bit weird to consume the // as part of the text rather than the keyword. That happens because the try( string "//" ), which is part of the end arg to manyTill, consumes the // when it succeeds. But maybe it is the most natural way to express the problem. parseKeyword :: Parser String parseKeyword = many1 (alphaNum <|> char '_') parseText :: Parser String parseText = manyTill anyChar ((try (string "//") >> return ()) <|> eof) parsePair :: Parser (String,String) parsePair = do k <- parseKeyword t <- parseText return (k,t) parseFile :: Parser [(String,String)] parseFile = do _ <- parseText -- to skip any text at beginning and 'sync up' p <- many parsePair return p