Simple gui app in scheme

gistfile1.scm

#lang scheme
(require scheme/gui/base)
(require framework)

(application:current-app-name "TestApp")
(preferences:set-default 'TestApp:size-preference '(600 400) 
                         (λ(size) (and (list? size)
                                       (andmap (λ(i) (positive? i)) size))))



(define my-app%
  (class (frame:size-pref-mixin (frame:standard-menus-mixin (frame:basic-mixin frame%)))
    (inherit get-area-container)
    
    (super-new [size-preferences-key 'TestApp:size-preference]
               [label "MyApp"]
               [min-width 200]
               [min-height 100])
    
    (let* ([window (get-area-container)]
           [vpane (new vertical-pane% [parent window] [alignment '(center center)])])
      (new message% [parent vpane] [label "Yeah yeah, hello world!"])
      (new button% [parent window] [label "Quit"] 
           [callback (λ(b e) (exit:exit))]))
    
    (frame:reorder-menus this)))

(send (new my-app%) show #t)