Using Haskell's map function to calculate the sum of a list

Question

Haskell

addm::[Int]->Int
addm (x:xs) = sum(x:xs)

I was able to achieve to get a sum of a list using sum fu

Answer 1

map can never be the primary tool for summing the elements of a container, in much the same way that a screwdriver can never be the primary tool for watching a movie. But you can use a screwdriver to fix a movie projector. If you really want, you can write

import Data.Monoid
import Data.Foldable

mySum :: (Foldable f, Functor f, Num a)
      => f a -> a
mySum = getSum . fold . fmap Sum

Of course, this is silly. You can get a more general, and possibly more efficient, version:

mySum' :: (Foldable f, Num a) => f a -> a
mySum' = getSum . foldMap Sum

Or better, just use sum, because its actually made for the job.