typeclass.js

var traits = {};

function trait(name, methods) {
    traits[name] = methods;
}

function struct() {
    var args = arguments;

    // インターフェイスを作成
    var interfaces = function() {};
    for (var j = 0; j < args[1].length; j++) {
        interfaces[args[1][j]] = {};
    }

    function find(x) {
        for (var y in interfaces) {
            if (x in traits[y]) return y;
        }
    }

    for (var x in args[2]) {
        // インターフェイスを取得
        interfaces[find(x)][x] = args[2][x];
    }

    return function() {
        var i = 0;
        for (var x in args[0]) {
            this[x] = arguments[i];
            i++;
        }
        for (x in interfaces) {
            this[x] = interfaces[x];
        }
    };
}

trait("Eq1", {
    eq1: ["fun", ["self"], "bool"]
});
trait("Eq2", {
    eq2: ["fun", ["self"], "bool"]
});

var I = struct({
    "x": "int"
}, ["Eq1", "Eq2"], {
    "eq1": function(s, a) {
        return s.x == a.x;
    },
    "eq2": function(s, a) {
        return s.x == a.x;
    }
});

var i = new I(10);
var j = new I(10);
console.log(i.x);
console.log(i.Eq1.eq1(i, j));
console.log(i.Eq2.eq2(i, j));