Monadic sugar in JavaScript using sweet.js macros

operator (>>=) 1 left { $a, $b } => #{ $a.bind($b) }
operator (>>) 1 left { $a, $b } => #{ $a.bind((_) => $b) }

function Just(value) {
    this.value = value;
}

Just.prototype.bind = function(fn) {
    return fn(this.value)
}

Just.prototype.toString = function() {
    return "Just(" + this.value + ")"
}

function Nothing(value) {}

Nothing.prototype.bind = function(_) {
    return this
}

Nothing.prototype.toString = function() {
    return "Nothing()"
}

function sqrtMaybe(x) {
    return x >= 0 ? new Just(Math.sqrt(x)) : new Nothing()
}

const result = sqrtMaybe(25)
    >>= (x) => sqrtMaybe(36)
    >>= (y) => new Just(x + y)

alert(result)   // => Just(11)

const result2 = sqrtMaybe(-1)
    >>= (x) => alert("This code won't be executed")

alert(result2)  // => Nothing()