! defining new instances in a namespace in the global scope
: <namespace> ( -- namespace )
    H{ } clone ;

VALUE: App
<namespace> App set-value

SYMBOLS: picker-view layout mouse-down ;

: add-property ( variable value -- )
    swap set ;

ALIAS: add-responder-method add-property

:: define-instance ( ns var value -- )
    ns [ value var set ] bind ;

App picker-view <view>

    layout { 100 100 10 50 } add-property
    mouse-down [| evt | drop beep t ] add-responder-method

define-instance

! ERROR: Generic word def>> does not define a method for the POSTPONE: f class.