JS functional calc

index.js

var five = num(5);
var one = num(1);

console.log(five(plus(one()))); //6

function plus(arg){
  return function(arg2){
    return arg + arg2;
  }
}

function num(val){
  return function(func){
    if (func === undefined){
      return val;  
    }
    return func(val);
  }
}