[Haskell-cafe] A function for Maybes

[Andrew Wagner]

:t liftM
forall r (m :: * -> *) a1. (Monad m) => (a1 -> r) -> m a1 -> m r
> liftM (+2) (Just 3
Just 5
 liftM (+2) Nothing
Nothing

(Thanks to allbery_b for contributing to the discussion on #haskell)

On 1/25/07, John Ky <newhoggy at gmail.com> wrote:
> Is there a built-in function that already does this?
>
> foo :: (a -> b) -> Maybe a -> Maybe b
> foo f m
>   | isNothing m = Nothing
>   | otherwise = Just (f (fromJust m))
>
> *Main> foo (+2) (Just 3)
> Just 5
> *Main> foo (+2) Nothing
> Nothing
>
> If so what is it?
>
> If not, what should I call it?
>
> Thanks
>
> -John
>
>
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe at haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
>
>
>