y-combinator.js

y-combinator.js

// Here's a simple lambda combinator; it'll turn the function passed in
// into a function which, when called, returns a recursible copy of itself.
function y_combinator(curried) {
    return function(f1){
        return curried(function () { f1(f1)(arguments) });
    }(function (f2) {
        return curried(function () { f2(f2)(arguments) });
    });
}

// Here's a use of that lambda combinator. We'll just print all the numbers
// in this list.
var numbers = [1, 2, 3];
y_combinator(function (recurse) {
    return function () {
        var number = numbers.shift();
        console.log("number: " + number);
        if (numbers.length) {
            return recurse();
        } else {
            return;
        }
    }
})();

// a more incorrect application of the y-combinator(), I'm sure: try to short-circuit
// async.waterfall.
// 
// Here's our actual list of tasks
var tasks = [f1, f2, f3, f4];

// a manager "task" which will stop executing tasks if one sets short_circuit.
var short_circuitable = [y_combinator(function(continue) {
    return function () {
        var task = tasks.shift();
        if (short_circuit) {
            return;  // perhaps: return function () {}
                     // depending on async.waterfall's mechanism
                     // for knowing "no more work, yo!"
        } else {
            return continue();
        }
    }
})];

// let 'er rip
async.waterfall(short_circuitable);

// standard syntax errors are in effect.

My big references for y-combinators are:

http://stackoverflow.com/questions/93526/what-is-a-y-combinator

and two of the linked articles:
http://mvanier.livejournal.com/2897.html
http://www.mail-archive.com/[email protected]/msg02716.html