Test.hx

class Test {
    static function main() {
        trace("Haxe is great!");
        var nya : Foo = new Foo(function (x : String) : Void {
            trace(x);
            // btw
            nya;
        });
        nya.say();
    }
}

class Foo {
    private var func : String -> Void;
    public function new(func : String -> Void) {
        this.func = func;
    }
    
    public function say() : Void {
        this.func("foo");
    }
}