import Data.Maybe (catMaybes)
list = ["hi", "blah", "foo"]
firstJust = head . catMaybes
selectOne f = firstJust . map f
myFunction :: String -> Maybe Int
myFunction = undefined
main = print $ selectOne myFunction list
catMaybes will take a list of Maybe a and reduce it to a list of a, throwing out all the Nothings.
As you'll learn from working with Maybe a lot, if you're casing off of a maybe value, there's probably a better way to do it. Functions like "catMaybes" and "maybe" and especially the Monad instance of Maybe are really helpful for avoiding this ugly branching logic.
On Thu, Nov 3, 2011 at 9:07 AM, Hugo Ferreira
<hmf@inescporto.pt> wrote:
I am considering something like:
selectOne f = take 1 . filter (\e -> case e of
Just _ -> True
_ -> False ) . map f
--
Michael Xavier
http://www.michaelxavier.net