On Dec 23, 2007, at 7:35 , Paulo J. Matos wrote:
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)
-- simple version, factor out common code
parseHeader3 bs = let (x1,bs') = parse' bs "first"
(x2,_ ) = parse' bs' "second"
in (x1,x2)
where
parse' s es = case BS.readInt $ BS.dropWhile (not . isDigit) s of
Nothing -> error $ "Couldn't find " ++ es ++ "
natural."
Just r -> r
-- this one uses MonadError; result is Either String (Int,Int)
parseHeader4 bs = do
(x1,bs') <- parse'' bs "first"
(x2,_ ) <- parse'' bs' "second"
return (x1,x2)
where
parse'' s es = case BS.readInt $ BS.dropWhile (not . isDigit) s of
Nothing -> fail $ "Couldn't find " ++ es ++ "
natural."
Just r -> return r
--
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 university KF8NH
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