[Haskell-cafe] Why is this strict in its arguments?

[Ryan Ingram]

On 12/6/07, Ryan Ingram <ryani.spam at gmail.com> wrote:
>
> On 12/6/07, Luke Palmer <lrpalmer at gmail.com> wrote:
> >
> > I have actually seen this pattern a lot recently.  Recently I have
> > started using a function:
> >
> > mergeMaybes :: (a -> a -> a) -> Maybe a -> Maybe a -> Maybe a
> > mergeMaybes f Nothing y = y
> > mergeMaybes f x Nothing = x
> > mergeMaybes f (Just x) (Just y) = Just (f x y)
>
>
> mergeMaybes = liftM2 -- from Control.Monad
>

Oh wait, not quite.  Didn't realize you were returning the intermediate
values in the "not nothing" case.

mergeMaybes f x y = liftM2 f `mplus` x `mplus` y
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