A modified zip function in Haskell that sums up the two elements of the input lists in the second item of the output tuple.

zip_sum.hs

--As modified from the Prelude:
zip_sum ::(Num a, Eq a)=> [a] -> [a] -> [(a,a)]
zip_sum []     _bs    = []
zip_sum _as    []     = []
zip_sum (a:as) (b:bs) = (a, (a + b) ) : zip_sum as bs

main = do
  print (zip_sum [0,1,2] [1,2,3])
  print (zip_sum [1,2,3,4,0,5,6] [1,2,3,4,5,6,0])

See my blog post.