[Haskell-cafe] Re: [Haskell] ANN: scan-0.1.0.3, a Haskell style scanner

[Sebastian Fischer]

Hello Christian,

On Apr 19, 2010, at 4:48 PM, Christian Maeder wrote:

> I like to announce a Haskell style scanner at
> http://hackage.haskell.org/package/scan
>
> Feedback is welcome.

I get lots of "multiple blanks" which I'd rather not "correct".

I often use multiple blanks to achieve vertical layout which is  
especially useful in combination with lhs2TeX [1] whose polycode mode  
requires multiple blanks to achieve proper indentation.

This code

     instance Eq a => Eq (Maybe a) where
       Nothing  ==  Nothing  = True
       Just x   ==  Just y   = x == y
       _        ==  _        = False

triggers this  scan  output:

     scan-test.hs:2:10: up to column 12 multiple (2) blanks
     scan-test.hs:2:14: up to column 16 multiple (2) blanks
     scan-test.hs:2:23: up to column 25 multiple (2) blanks
     scan-test.hs:3:9: up to column 12 multiple (3) blanks
     scan-test.hs:3:14: up to column 16 multiple (2) blanks
     scan-test.hs:3:22: up to column 25 multiple (3) blanks
     scan-test.hs:4:4: up to column 12 multiple (8) blanks
     scan-test.hs:4:14: up to column 16 multiple (2) blanks
     scan-test.hs:4:17: up to column 25 multiple (8) blanks

I very much prefer the previous indentation over the following version  
stripped down by  scan -  (using the hyphen option):

     instance Eq a => Eq (Maybe a) where
       Nothing == Nothing = True
       Just x == Just y = x == y
       _ == _ = False

I did not find a way to configure  scan  to ignore "multiple blanks".  
Did I miss it?

Sebastian

[1]: http://people.cs.uu.nl/andres/lhs2tex/

-- 
Underestimating the novelty of the future is a time-honored tradition.
(D.G.)