fold-zip 融合 ref: http://qiita.com/nobsun/items/37d6cc2505af0a3a252f

file0.txt

(foldr (⊕) z .) . zipWith (⊗) 
⇔
foldr (⊛) (const z)
  where
    (x ⊛ k) []     = z
    (x ⊛ k) (y:ys) = (x ⊗ y) ⊕ k ys

file1.txt

sumtimes xs ys = sum $ zipWith (*) xs ys

file2.txt

sumtimes = (foldr (+) 0 .) . zipWith (*)

sumtimes.hs

sumtimes = foldr (⊛) (const 0)
  where
    (x ⊛ k) []     = 0
    (x ⊛ k) (y:ys) = (x * y) + k ys