andyhd

function lens(get, set) {
  var f = function (a) { return get(a); };
  f.set = set;
  f.mod = function (f, a) { return set(a, f(get(a))); };
  return f;
}

var first = lens(
  function (a) { return a[0]; },
  function (a, b) { return [b].concat(a.slice(1)); }

buzzdecafe

// clean and pure:
function cons(x, y) {
    return function(pick) {
        return pick(x, y);
    }
}

// does more stuff:
function cons(x, y) {
    var fn = function(pick) {

ForbesLindesay

Real World Specification

(aka "Algebraic JavaScript Specification")

This project specifies the behavior of a number of methods that may optionally be added to any object. The motivation behind this is to encourage greater code reuse. You can create functions that just rely on objects having implementations of the methods below, and in doing so you can make them work with a wide variety of different, but related data structures.

Definitions

For the purposes of this, spec, an "entity" is an object that has an [[equivalent]] operation (see bellow) and may implement some or all of the other methods.