Array.pure = function(x) {

  return [x];

}

Array.prototype.bind = function(f) {

  return this.reduce((acc, a) => acc.concat(f(a)), [])

};

​

// range (1, 10) = [1, 2, 3, ..., 10]

function range(from, to) {

  return [for (i of Array(to).keys()) from + i]

}

​

// note difference between map and bind

​

console.log(

  [1, 2, 3, 4, 5].map(x => range(1, x))

);

​

console.log(

  [1, 2, 3, 4, 5].bind(x => range(1, x))

);