applicative.js

// :: String -> String
function concat(a){ return function(b){
  return a + b
}}

// :: (a -> b -> c) -> (b -> a -> c)
function flip(f){ return function(a){ return function(b) {
  return f(b)(a)
}}}

// :: [[a]] -> [a]
function flatten(xss) {
  return xss.reduce(function(ys, xs) {
    return ys.concat(xs)
  }, [])
}

// :: [a] -> (a -> [b]) -> [b]
function chain(xs){ return function(f) {
  return flatten(xs.map(f))
}}

// :: [(a -> b)] -> [a] -> [b]
function ap(fs){ return function(b) {
  return chain(b)(function(x) {
    return fs.map(function(f) {
      return f(x)
    })
  })
}}


var xs = [['hello', 'hi'], ['there', 'stranger']]
var greetings = xs[0].map(flip(concat(' ')) // adds a whitespace after every greeting
var what = xs[1]

ap(greetings.map(concat))  // transforms each greeting in a function String -> String
  (what)                   // distributes those functions over the list of things