Oh, and a little background. fmap comes from the Functor typeclass, and lists have an instance of Functor so the empty list case is handled automatically. Then I used "take 1" to get the head in a safe way, e.g. defaulting to empty list if the output of fmap is empty. M. Martin Vlk:
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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