[Haskell-cafe] type checking that I can't figure out ....

[Michael Snoyman]

On Wed, Jun 3, 2009 at 8:42 AM, Daniel Fischer <daniel.is.fischer at web.de>wrote:

> Am Mittwoch 03 Juni 2009 06:12:46 schrieb Michael Snoyman:
>
> > I made two changes:
> >
> > 1. You had the arguments to M.lookup backwards.
> > 2. lookup does not return any generalized Monad, just Maybe (I think that
> > should be changed).
>
> Data.Map.lookup used to return a value in any monad you wanted, I believe
> until 6.8
> inclusive.
> I don't think it's going to change again soon.
>

Is there a reason why it only returns in the Maybe monad? I often times have
to write a liftMaybe function to deal with that.

Michael
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