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

2007-11-21 Thread Berlin Brown 
On Nov 18, 2007 8:01 PM, Thomas Schilling [EMAIL PROTECTED] wrote:
 On Sun, 2007-11-18 at 19:37 -0500, Berlin Brown wrote:
  On Nov 18, 2007 7:32 PM, Berlin Brown [EMAIL PROTECTED] wrote:
   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
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe

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

2007-11-21 Thread Brandon S. Allbery KF8NH 


On Nov 22, 2007, at 0:50 , Berlin Brown wrote:


token :: Parser - Parser String
token p = do r - p
  whiteSpace
  return $ String r


You have an indentation problem:  whiteSpace and return should be at  
the level of r, not p.


--
brandon s. allbery [solaris,freebsd,perl,pugs,haskell] [EMAIL PROTECTED]
system administrator [openafs,heimdal,too many hats] [EMAIL PROTECTED]
electrical and computer engineering, carnegie mellon universityKF8NH


___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe

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

2007-11-18 Thread Berlin Brown 
On Nov 18, 2007 7:32 PM, Berlin Brown [EMAIL PROTECTED] wrote:
 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

 I added this code here and I think it works (I replaced the name
 parseSpaces with his spaces function).  But, if I start a line with a
 comment, it errors out with unbound variable.  Anybody have any ideas?

 -- Added the ';'
 symbol :: Parser Char
 symbol = oneOf ;!$%|*+-/:=[EMAIL PROTECTED]

 --
 -- Handle whitespace and comments
 parseSpaces :: Parser ()
 parseSpaces = (try oneLineComment) | whiteSpace | return ()
 where
   whiteSpace = do skipMany1 space
   parseSpaces
   oneLineComment = do { try (string ;)
   ; skipMany (satisfy (/= '\n'))
   ; parseSpaces
   }

 http://halogen.note.amherst.edu/~jdtang/scheme_in_48/tutorial/overview.html




Sorry, I am using the full scheme parser in this example:
http://halogen.note.amherst.edu/~jdtang/scheme_in_48/scheme_in_48.zip


-- 
Berlin Brown
http://botspiritcompany.com/botlist/spring/help/about.html
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe

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

2007-11-18 Thread Thomas Schilling 
On Sun, 2007-11-18 at 19:37 -0500, Berlin Brown wrote:
 On Nov 18, 2007 7:32 PM, Berlin Brown [EMAIL PROTECTED] wrote:
  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.

___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe