UnitJS/async.js

function Async() {
	return {
		apply: apply,
		bind: bind,
		fail: fail,
		http: http,
		map: map,
		parallel: parallel,
		run: run,
		sequence: sequence,
		wait: wait,
		wrap: wrap
	};

	function apply(f, x) {
		return function(g) {
			g(f(x));
		};
	}

	function bind() {
		var m, steps, i;
		if(arguments.length < 1) {
			return wrap();
		}
		m = arguments[0];
		steps = arguments;
		i = 1;
		return function(f) {
			var step = function(x) {
				if(i < steps.length) {
					steps[i++](x)(step);
				} else {
					return f(x);
				}
			}
			m(step);
		};
	}

	function fail(message) {
		return function(f) {
			console.log(message);
		}
	}

	function map(mapper) {
		return function(x) {
			return function(f) {
				f(mapper(x));
			};
		};
	}

	function parallel() {
		var threads = arguments;
		var pending = threads.length;
		var results = [];
		var returned = [];
		return function(f) {
			var useResult = function(i) {
				return function(x) {
					if(!returned[i]) {
						results[i] = x;
						returned[i] = true;
						pending--;
						if(pending < 1) {
							f(results);
						}
					}
				};
			};
			for(var i = 0; i < threads.length; i++) {
				threads[i](useResult(i));
			}
		};
	}

	function run() {
		var m;
		if(arguments.length == 1) {
			m = arguments[0];
		} else {
			m = sequence.apply(null, arguments);
		}
		m(function() {});
	}

	function sequence() {
		var steps = arguments;
		var i = 0;
		return function(f) {
			var step = function(x) {
				if(i < steps.length) {
					steps[i++](step);
				} else {
					f(x);
				}
			}
			step();
		};
	}

	function wait(delay) {
		return function(f) {
			setTimeout(f, delay);
		};
	}

	function wrap(x) {
		return function(f) {
			f(x);
		};
	}

	function http(query) {
		return function(f) {
			var xhr = new XMLHttpRequest();
			xhr.addEventListener('load', function() {
				f(this);
			});
			xhr.open(query.method, query.url);
			if(query.method == 'POST') {
				xhr.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
			}
			xhr.send(query.body);

		};
	}

}