Question

How can I do the sum of elements in a list at the same position?
For example:

[[2,3,4],[5,6,7],[8,9,10]]=[15,18,21]

Thanks

Answer 1

Try:

sumIn :: Num a => [[a]] -> [a]
sumIn = foldl (zipWith (+)) (repeat 0)

Note that if the argument is an empty list, the result is an infinite list of zeros. So you may want to treat this case separately, for example

sumIn :: Num a => [[a]] -> [a]
sumIn [] = []
sumIn xs = foldl (zipWith (+)) (repeat 0) xs