And here's another vote for Maybe. That's almost always the return
type that you want anyway, so the inconvenience in minimal.
And anyone who wants the old behavior can easily make a utility
function that provides it.
The current behaviour encourages sloppy programming.
-- Lennart
On Wed, May 28, 2008 at 7:51 PM, Duncan Coutts
On Wed, 2008-05-28 at 11:11 +0100, Conor McBride wrote:
Ross Paterson wrote:
Several functions on containers used to have types like lookup :: (Ord k) => k -> Map k a -> Maybe a but these were generalized to lookup :: (Monad m, Ord k) => k -> Map k a -> m a The proposal is to change these signatures back, specializing them to Maybe.
I'm all for Maybe in the question Monad VS Maybe.
Me too. (+1) for Ross's proposal.
If we need any more (+1) votes you can count mine.
Also, it's not entirely clear whether MonadZero is the most general abstraction. Is ApplicativeZero better? Or something else?
Maybe is the most general abstraction. Requiring (>>=), or even (<*>) seems excessive. What we need is "any f with zero and return", so why not pick the canonical, initial, inductively defined such thing?
Good. I like that argument.
As others have pointed out, it's easy to lift maybe into something else when that's needed.
maybe :: a -> (b -> a) -> Maybe b -> a
Duncan
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