Roy monoid type-class with JS output

monoid.js

var stringMonoid = {
    "append": function(x, y) {
        return x + y;
    },
    "empty": ""
};
console.log(stringMonoid.append(stringMonoid.append("Hello!", stringMonoid.empty), stringMonoid.empty));
var f = function(Monoid, x) {
    return Monoid.append(Monoid.empty, x);
};
var g = function(Monoid, x) {
    return f(Monoid, x);
};
console.log(g(stringMonoid, "TEST"));
//@ sourceMappingURL=monoid.js.map

monoid.roy

typeclass Monoid #a {
  append: Function(#a, #a, #a)
  empty: #a
}

instance stringMonoid = Monoid String {
  append: \x y -> x ++ y
  empty: ""
}

console.log (append (append "Hello!" empty) empty)

let f x = append empty x
let g x = f x

console.log (g "TEST")

zero!