Mimic Haskell with Javascript in Functional Programming and Composition

haskell.js

function _(...fns) {
  return x => fns.reverse().reduce((reduced, f ) => f(reduced), x )
}

const sum = arr => arr.reduce((a, b) => a + b, 0 )
const filter = (fn, arr) => arr === undefined ? b => filter(fn, b) : arr.filter(fn)

// export

usage.js

import 'haskell.js'
// Haskell: sum . filter(>4) [5, 6, 3]
_(sum, filter(x => x> 4))([5, 6, 3])