How about:

computeHead f = take 1 . fmap f

Martin

Dennis Raddle:

> What would be an elegant way of writing this
>
> computeHead :: (a -> [b]) -> [a] -> [b]
>
> Where when [a] is null, it returns a null list, but when [a] contains one
> or more elements, it applies the given function to the head of a and
> returns that? Is there some existing typeclass operator that facilitates
> this?
>
> You can write
>
> computeHead _ [] = []
> computeHead f (x:_) = f x
>
> But that first line seems suspicious to me... it makes me think about how
> in the list Monad, an empty list falls through. But I can't quite make it
> work.
>
>
>

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