z-combinator

Z Combinator for self-referencing anonymous functions

Z Combinator

Version: 0.1.1
Master build:
Develop build:

This library provides a utility function to support the creation of self-referencing anonymous functions.
It can be installed in whichever way you prefer, but I recommend NPM.

The Z Combinator is the same, in principle, as the Y Combinator except it works in languages with applicative (eager) order of execution (arguments are evaluated before the function call) just like JavaScript.

For more information about the Z Combinator please read Douglas Crockford's "The Little JavaScripter".

var z = require('z-combinator');
 
// Factorial 
var factorial = z(function(fn) {
    return function(n) {
        return 2 >= n ? n : n * fn(- 1);
    }
});
 
factorial(2) // => 2 
factorial(3) // => 6 
factorial(4) // => 24 
factorial(5) // => 120 

Just as you would with any other recursive function, make sure you include some sort of break condition. If you miss it out, the function will recur indefinitely.

var z = require('z-combinator');
 
z(function(fn) {
    return function(n) {
        return fn(+ 1); // <= Unconditional recursion 
    };
})(0);
// => Error: Maximum call stack exceeded 
 
z(function(fn) {
    return function(n) {
        return 100 <= n ? n : fn(+ 1); // <= Conditional recursion 
    };
})(0);
// => 100 

I accept contributions to the source via Pull Request, but passing unit tests must be included before it will be considered for merge.

$ make install
$ make tests

If you have Vagrant installed, you can build the dev environment to assist development. The repository will be mounted in /srv.

$ vagrant up
$ vagrant ssh
 
Welcome to Ubuntu 12.04 LTS (GNU/Linux 3.2.0-23-generic x86_64)
$ cd /srv

The content of this library is released under the MIT License by Andrew Lawson.
You can find a copy of this license at http://www.opensource.org/licenses/mit or in LICENSE