How to do callbacks to methods

In the app below none of the callbacks works, neither in the bind calls
nor the -command. I am using Tcl/Tk 9.0b2 on Linux. How can I make these
callbacks work?

#!/usr/bin/env wish9
tk appname "Test App"
oo::class create App {
    constructor {} {
        wm withdraw .
        wm title . [tk appname]
        grid [ttk::button .quitButton -text Quit -underline 0 \
              -command {my on_quit}]
        bind <Escape> {my on_quit}
        bind <Alt-q> {my on_quit}
    }
    method on_quit {} {
        destroy .
    }
    method show {} {
        wm deiconify .
        raise .
    }
}
set application [App new]
$application show