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

[Paulo J. Matos]

On Dec 23, 2007 12:32 PM, Paulo J. Matos <pocm at soton.ac.uk> wrote:
> Hello all,
>
> It is either too difficult to get two integers of a bytestring, in
> which case something should be done to ease the process or I should
> learn much more Haskell. I guess the latter is the correct guess.
>
> I have a bytestring containing two naturals. I was to get them as
> efficiently as possible. Here's my code:

Just tried a better one, what do you think of this:
parseHeader2 :: BS.ByteString -> (Int, Int)
    parseHeader2 bs =
        case (BS.readInt $ BS.dropWhile (not . isDigit) bs) of
          Nothing -> error "Couldn't find first natural."
          Just (x, rest) ->
              case (BS.readInt $ BS.dropWhile (not . isDigit) rest) of
                Nothing -> error "Couldn't find second natural."
                Just (y, _) -> (x, y)

> parseHeader :: BS.ByteString -> (Int, Int)
> parseHeader bs =
>         let first = BS.readInt $ BS.dropWhile (not . isDigit) bs
>         in
>           if(isNothing first)
>           then
>               error "Couldn't find first natural."
>           else
>               let second = BS.readInt $ BS.dropWhile (not . isDigit) $
> snd $ fromJust first
>               in
>                 if(isNothing second)
>                 then
>                     error "Couldn't find second natural."
>                 else
>                     (fst $ fromJust first, fst $ fromJust second)
>
> This seems to work:
> > parseHeader $ BS.pack "hello 252 359"
> (252,359)
>
> Is there a better way?
>
> Cheers,
>
> --
> Paulo Jorge Matos - pocm at soton.ac.uk
> http://www.personal.soton.ac.uk/pocm
> PhD Student @ ECS
> University of Southampton, UK
>



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