Re: [Haskell-cafe] Re: Comments on reading two ints off Bytestring

24 Dec 2007


      On Dec 24, 2007 11:55 AM, Paulo J. Matos  wrote:
...
On Dec 23, 2007 12:44 PM, Isaac Dupree  wrote:
...
-- this should work too
parseHeader3 :: BS.ByteString -> Maybe (Int, Int)
--note accurate type signature, which helps us use Maybe failure-monad,
--although losing your separate error messages
Oh gee, I just noticed that my type sig is in fact not correct. How
come GHC doesn't complain?
...
parseHeader3 bs = do
   (x, rest) <- BS.readInt $ BS.dropWhile (not . isDigit) bs
   (y, _) <- BS.readInt $ BS.dropWhile (not . isDigit) rest
   return (x, y)
What happens then if the first BS.readInt return Nothing???
Ok, got it, I'm not returning a maybe. That's it then.
Still, the first question remains... what happens to (x, rest) if
BS.readInt returns Nothing.

-- 
Paulo Jorge Matos - pocm at soton.ac.uk
http://www.personal.soton.ac.uk/pocm
PhD Student @ ECS
University of Southampton, UK