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
On Jan 25, 2007, at 9:15 , John Ky 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))
Nothing specific to Maybe, because the more general liftM (over
monads) or fmap (over
fmap. e.g.:
Prelude fmap ('c':) (Just a)
Just ca
Prelude fmap ('c':) Nothing
Nothing
Prelude
/g
On 1/25/07, John Ky [EMAIL PROTECTED] 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
: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 [EMAIL PROTECTED] wrote:
Is there a built-in function that already does this?
Thanks
-John
On 1/26/07, Brandon S. Allbery KF8NH [EMAIL PROTECTED] wrote:
On Jan 25, 2007, at 9:15 , John Ky 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))
Nothing
