callback hellを避けるけど同期処理のようにもしない奴

hoge.js

// utility ----------------------------------------------------------
function isGenerator(o) {
	return (typeof o === "object") && (typeof o.next === "function");
}
function isPromise(o) {
	return (typeof o === "object") && (typeof o.then === "function");
}
function isTag(o) {
	return (typeof o === "object") && (o.tag === "tag");
}

// wrapper ----------------------------------------------------------
function tag(promise) {
	return {tag: "tag", value: promise};
}
function untag(tag) {
	return isTag(tag) ? tag.value : null;
}

// main -------------------------------------------------------------
function lazy(g) {
	return new Promise(function(resolve, reject) {
		window.setTimeout(function() {
			C$(g).then(resolve, reject);
		}, 1000 + Math.random() * 100);
	});
}

function C$sub(g, o, resolve, reject) {
	while(true) {
		var y = g.next(o);
		o = y.value;
		if(y.done) {
			return resolve(o);
		} else if(isGenerator(o)) {
			o = tag(lazy(o));
		} else if(isPromise(o)) {
			o = tag(o);
		} else if(isTag(o)) {
			var promise = untag(o);
			return promise.then(function(v) {
				C$sub(g, v, resolve, reject);
			}, reject);
		} else {
			return resolve(o);
		}
	}
}

function c(g) {
	return new Promise(function(resolve, reject) {
		C$sub(g, null, resolve, reject);
	});	
}

// test -------------------------------------------------------------
function *fa(x) {
	console.log("fa", x);
	return x;
}

function fb(x, delay) {
	console.log("fb", x, delay);
	return new Promise(function(resolve, reject) {
		window.setTimeout(resolve.bind(window, x), delay);
	});
}

function *f() {
	console.log("f","1");
	var a$ = yield fa(1);
	var b$ = yield fb(3, 1000 + Math.random() * 100);
	console.log("f","2");
	var ret = (yield a$) + (yield b$);
	console.log("f","3", ret);
	return ret;
}

c(f()).then(console.log.bind(console), console.error.bind(console));