On 2008 May 11, at 22:42, Don Stewart wrote:
ok:
Maybe types force you to deal with it, while simultaneously providing convenience functions to help you deal with it.
I readily grant that Maybe is a wonderful wonderful thing and I use it freely and voluntarily. BUT it should not dominate the code.
Consider Haskell's getChar and hGetChar. They DON'T return Maybe Char; they raise an exception at end of file. You have to keep testing isEOF/ hIsEOF before each character read, as if we had learned nothing since Pascal. Arguably, maybeGetChar :: IO (Maybe Char) and hMaybeGetChar :: Handle -
IO (Maybe Char) would be a good idea, at least then one could easily set up some combinators to deal with this nuisance.
Thankfully its easy to lift IO-throwing things into a safer world.
import Control.Exception import Prelude hiding (getChar) import qualified Prelude as P
getChar :: IO (Maybe Char) getChar = handle (const (return Nothing)) (Just `fmap` P.getChar)
And it's a monad, so it doesn't have to dominate the code; you can write your code monadically and let the scaffolding deal. -- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allbery@kf8nh.com system administrator [openafs,heimdal,too many hats] allbery@ece.cmu.edu electrical and computer engineering, carnegie mellon university KF8NH