: ( -- namespace ) H{ } clone ; VALUE: App App set-value SYMBOLS: picker-view layout mouse-down ; : add-property ( variable value -- ) swap set ; ALIAS: add-responder-method add-property App [ picker-view layout { 100 100 10 50 } add-property mouse-down [| evt | drop beep t ] add-responder-method swap set ] bind ! ERROR: Generic word def>> does not define a method for the POSTPONE: f class.