Idiomatic way to sum a list of Maybe Int in haskell

Question

Is there a more idiomatic way to implement the following? I feel like I\'m missing a way to get rid of the lambda, but couldn\'t figure out a way to convert it to point-free. Ma

Answer 1

I'd just use sequence from Control.Monad:

> fmap sum $ sequence [Just 3, Just 4]
Just 7
> fmap sum $ sequence [Just 3, Just 4, Nothing]
Nothing

For the point-free form:

sumMaybe :: Num a => [Maybe a] -> Maybe a
sumMaybe = fmap sum . sequence