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] [EMAIL PROTECTED]
system administrator [openafs,heimdal,too many hats] [EMAIL PROTECTED]
electrical and computer engineering, carnegie mellon university KF8NH
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