Repeated diamonds shape

JS

var diamonds = new warp9.Cell("1");
var result = new warp9.Cell(1);
var dispose, updates;

warp9.render(placeholder, ["div",
    ["div",
        ["label", {"for": "d"}, "Enter number of diamonds:"],
        ["input-text", {"id": "d"}, diamonds],
        ["button", {"!click": function(){
            if (dispose) dispose();
            if (parseInt(diamonds.get())>0) {
                var source = new warp9.Cell();
                var target = repeatDiamondShape(source, parseInt(diamonds.get()));
                updates = 0;
                dispose = target.onSet(function(){
                    result.set(++updates);
                });
                source.set(2);
            } else result.unset();
        }}, "Calc updates"]
    ],
    result.lift(function(result){
        return ["span", "Expected one update & got " + result]
    }).coalesce(["span", "Should be an integer above 0"])
]);

function repeatDiamondShape(seed, n) {
    if (n==0) return seed;
    var s1 = warp9.do(function(){ return seed.get() + 1; });
    var s2 = warp9.do(function(){ return seed.get() + 1; });
    return repeatDiamondShape(warp9.do(function(){
        return s1.get() + s2.get();
    }), n-1);
}