haskell
foldl :: (a -> b -> a) -> a -> [b] -> a
foldl step zero (x:xs) = foldl step (step zero x) xs
foldl _ zero [] = zero
js
function foldl(step, zero, arr) {
return arr.length > 0 ? foldl(step, step(zero, arr.shift()), arr) : zero
}
console.log(foldl((x, y)=> x + y, 1, [1,2,3,4,5]))
``