Re: [Haskell-cafe] Re: Scheme in Haskell, Parsec Example, how to add scheme comments

On Nov 18, 2007 8:01 PM, Thomas Schilling wrote:

On Sun, 2007-11-18 at 19:37 -0500, Berlin Brown wrote:

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On Nov 18, 2007 7:32 PM, Berlin Brown wrote:

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I am sure many of you have looked at the scheme in haskell example that is on the web by Jonathan Tang. If you are familiar with the code, I need a little help trying to add scheme style comments:

"; This is my comment"

The preferred way to do that is to use a token helper function:

token :: P a -> P a token p = do r <- p whiteSpace return r

-- or, if you add a Control.Applicative instance for your -- parser type, this is just: token p = p <* whiteSpace

Then you handle comments as whitespace:

whiteSpace :: P () whiteSpace = skipMany $ spaces <|> (char ';' >> skipMany (satisfy (/='\n')))

Then you just use that like this:

symbol :: P String symbol = token $ many1 $ satisfy $ not . (`elem` "()[]; ")

See also Parsec's TokenParser.

token :: Parser -> Parser String token p = do r <- p whiteSpace return $ String r I know I am being lazy, but what am I missing in your pseudo code: I tried playing with your example but kept getting these errors: Parsec3.hs:23:13: The last statement in a 'do' construct must be an expression at the token line. -- Berlin Brown http://botspiritcompany.com/botlist/spring/help/about.html