thunk.js

/*
 * thunk ~= promise
 * thunkのforceは別スレッド (投機的実行)
 */

function Thunk (thunk) {
    this.thunk = thunk;
    this.val = null;
    this.ff  = [];
}
Thunk.prototype.done = function (f) {
    this.ff.push(f);
    if (this.val) this.exec();
};
Thunk.prototype.exec = function () {
    var v = this.val;
    if (v) this.ff.map(function (f) { f(v); });
    this.ff = [];
};
Thunk.prototype.resolve = function () {
    if (this.val) return null;
    this.val = this.thunk();
    this.exec();
    return null;
};




function add (f, x, y) {
    x.done(function (x) {
        y.done(function (y) {
            f(x + y);
        })});
}

var a = Thunk(function () { return 5; });
var b = Thunk(function () { return 4; });
spawn(function () { a.resolve(); });
spawn(function () { b.resolve(); });
add(halt, a, b);