puffnfresh / brushtail Goto Github PK

This will make contribution a whole lot easier.

For some reason, all function expressions are ignored, even though NFEs have letrec semantics.

Put it on your website, in your blog, or even on github pages if you must. Just create an example people can play with, without having to pull.

Would be great to be able to just add it as a dependency.

If the function to transform has a label tco it gets shadowed:

function a(n) {
   tco: {
     return a(n);
   }
}

function a(n) {
    var __tcor;
    tco:
        while (true) {
            tco: {
                {
                    var __n = n;
                    n = __n;
                    continue tco;
                }
            }
        }
    return __tcor;
}

One of the key advantages for tail recursion is often that the compiler can find ways to optimize the loop to increase performance. But unfortunately this performance boost is destroyed by the closure in the mutated version. By removing the closure there is a massive performance increase on my machine around 800%.

http://jsperf.com/tail-recursion-test

Question is, are there efforts to remove the closure?

The following code breaks.

function factorial_cps(n, k) {
  if (n === 0) return k(1);
  return factorial_cps(
    n - 1, 
    function(result) { 
      return k(n * result); 
    });
}


function identity(x) { return x; }

var f = factorial_cps(5, identity); // 120

console.log(f); 

The problem is the

    __k = function (result) {
                    {
                        __tcor = k(n * result);
                        break tco;
                    }}

Which simply doesn't work. I guess there is no trivial solution for that but it would be very cool to be able to transform CPS code.

We can no longer be sure these are tail calls; they likely aren't. We can use escope again here. Either way, it should take into account variable declarations, function declarations, and parameter names that may shadow the function name.

Icedcoffeescript would go great with brushtail.
maxtaco/coffee-script#81

Shouldn't be too tricky. Traverse the AST looking for identifiers, store them in a set and try generating a fresh identifier.