puffnfresh/brushtail

---

puffnfresh/brushtail.json

{
  "createdAt": "2012-12-08T08:49:42Z",
  "defaultBranch": "master",
  "description": "JS AST rewriter for tail call elimination",
  "fullName": "puffnfresh/brushtail",
  "homepage": "http://brushtail.brianmckenna.org/",
  "language": "JavaScript",
  "name": "brushtail",
  "pushedAt": "2013-07-24T07:58:14Z",
  "stargazersCount": 135,
  "topics": [],
  "updatedAt": "2025-10-23T12:11:39Z",
  "url": "https://github.com/puffnfresh/brushtail"
}

Brushtail

Tail call optimisation for JavaScript.

Examples

example.js:

function count(from, to) {
    if(from >= to)
        return from;

    return count(from + 1, to);
}

console.log(count(0, 1000000));

Is rewritten into:

function count(from, to) {
    var __tcor;
    tco:
        while (true) {
            if (from >= to) {
                __tcor = from;
                break tco;
            }
            {
                var __from = from + 1, __to = to;
                from = __from;
                to = __to;
                continue tco;
            }
        }
    return __tcor;
}
console.log(count(0, 1000000));

Using the command-line tool:

$ brushtail example.js | node
1000000

For comparison, without the command-line tool:

$ node example.js

brushtail/example.js:1
n (exports, require, module, __filename, __dirname) { function count(from, to)
                                                                    ^
RangeError: Maximum call stack size exceeded

API

brushtail.tco(content)

Takes a JavaScript program as a String. Returns a String with a tail call optimised program.

brushtail.mutateAST(ast)

Takes a Mozilla Parser AST and mutates away tail calls.

brushtail.optimizeFunction(functionDeclaration)

Takes a function declaration in Mozilla Parser AST form and mutates away tail calls.

License

MIT