Yeah, it's actually much, much simpler to do it in Objective-C in this case.
[UIView animateWithDuration:0.5f animations:^{ // Do something }];
UIView.animateWithDuration(0.5, animations:lambda { //do something })
in RubyMotion. Basically the same.
UIView.animateWithDuration(0.5, animations:lambda { //do something })
in RubyMotion. Basically the same.