in lib/boleite/src/boleite/gui/widget.cr:30: no overload matches 'Boleite::GUI::Widget::Signal_state_change#on' with type Proc(Nil)
Overloads are:
 - Boleite::GUI::Widget::Signal_state_change#on(&block)
 - Boleite::GUI::Widget::Signal_state_change#on(sink : Cute::Sink(U))

      state_change.on ->on_state_change