Spec for an extension to javascript that makes it purely functional (with the exception of global variables)

pure.js

define a = b, // global.a = b;
       c = d; // global.c = d;

define f(x) { // global.f = function(x) {
              //   return;
}             // }; global.f.name = "f";
/* only globals can be reassigned, and only with the `define` keyword */

let (a = b, c = d) { // (function() { var a = b, c = d; (function(a, c) {
  console.log(a, c); //   return console.log(a, c);
}                    // }(a, c)); }());

[          // [
  1, 2, 3, //   1, 2, 3,
  4, 5, 6  //   4, 5, 6
]          // ]

[        // {
  a = b, //   a: b,
  c = d  //   c: d,
]        // }
/* for consistancy with other definitions, and array literal syntax, since objects are more similar to arrays than functions */

var x = y; // #<ERROR: illegal variable declaration>

let (a = b, c = d) { // (function() { var a = b, c = d; (function(a, c) {
  a = 5;             //   #<ERROR: illegal assignment>
}                    //

let (fn = {              // (function() { var fn = function() {
       console.log("x"); //   return console.log("x");
     }) {                // }; return (function(fn) {
  fn();                  //   return fn();
}                        // }(fn)); }());

`+5` // (function($implicit) { return $implicit + 5; })

[`*2` | [1, 2, 3, 4, 5, 6]; `>2`] // $comprehend((function($implicit) { return $implicit * 2; }), [1, 2, 3, 4, 5, 6], (function($implicit) { return $implicit > 2; }))

if (1 == 1) {           // (function() { if (1 === 1) {
  console.log("1 = 1"); //   return console.log("1 = 1");
}                       // }
else {                  // else {
  console.log("awww");  //   return console.log("awww");
}                       // } }());

console.log(cond { // console.log((function() {
  (1 == 1) {       //   if (1 === 1) {
    "yay";         //     return "yay";
  }                //   }
  (1 == 2) {       //   else if (1 === 2) {
    "shoot";       //     return "shoot";
  }                //   }
  else {           //   else {
    "wtf";         //     return "wtf";
  }                //   }
});                // }()));

switch (x) {          // (function() { switch (x) {
  case (1, 2) {       //   case 1: case 2:
    "1 or 2";         //     return "1 or 2";
  }                   //     break;
  case (3) {          //   case 3:
    "3";              //     return "3";
  }                   //     break;
  else {              //   default:
    "something else"; //     return "something else";
  }                   // }
}                     // }());

for (var i = 0; i < arr.length; i++) { // #<ERROR: illegal loop>
  console.log(arr[i]);                 // 
}                                      // 

for (i <- arr) {       // (function() { var $_ret = []; for (var i = 0; i < arr.length; i++) { $_ret.push((function() {
  console.log(arr[i]); //   return console.log(arr[i]);
}                      // }())); } return $_ret; }());

for (i = val <- arr) { // (function() { var $_ret = []; for (var i = 0; i < arr.length; i++) { var val = arr[i]; $_ret.push((function() {
  console.log(val);    //   return console.log(val);
}                      // }())); } return $_ret; }());

for (key <= obj) {       // (function() { var $_ret = []; for (var key in obj) { $_ret.push((function() {
  console.log(obj[key]); //   return console.log(obj[key]);
}                        // }())); } return $_ret; }());

for (key = val <= arr) { // (function() { var $_ret = []; for (var key in arr) { var val = obj[key]; $_ret.push((function() {
  console.log(val);      //   return console.log(val);
}                        // }())); } return $_ret; }());

/* all the loop constructs above are just syntactic sugar for recursion, which is what should be used for more complex loops */
/* it is intentional that none of these work with `break` or `continue`. That shoul be done with recursion. */