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

On 12/6/07, Ryan Ingram wrote:

On 12/6/07, Luke Palmer 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