func preorder(t) {
    t ? [t[0], __FUNC__(t[1])..., __FUNC__(t[2])...] : [];
}

func inorder(t) {
    t ? [__FUNC__(t[1])..., t[0], __FUNC__(t[2])...] : [];
}

func postorder(t) {
    t ? [__FUNC__(t[1])..., __FUNC__(t[2])..., t[0]] : [];
}

func depth(t) {
    var a = [t];
    var ret = [];
    while (a.len > 0) {
        var v = (a.shift \\ next);
        ret « v[0];
        a += [v[1,2]];
    };
    return ret;
}

var x = [1,[2,[4,[7]],[5]],[3,[6,[8],[9]]]];
say "pre:   #{preorder(x)}";
say "in:    #{inorder(x)}";
say "post:  #{postorder(x)}";
say "depth: #{depth(x)}";