deep-currying.js

function currying(fun) {
  function curryingIter(fun, len) {
    if (len < 2) {
      return fun
    }
  
    return curryingIter(function() {
      var args = [].slice.call(arguments)
      return function(x) {
        args.push(x)
        return fun.apply(null, args)
      }
    }, len - 1) 
  }
  
  return curryingIter(fun, fun.length)
}

// use
function add(x, y, z) {
  return x + y + z
}

var newAdd = currying(add)

newAdd(2)(3)(4) // 9