(setq dsf/screen-one (lambda nil
  (block nil
    (dsf/screen 'one "Screen One")
    (dsf/action 'switch "Switch to Two" 'S '(dsf/screen-two))
    (dsf/default-action 'switch)
    (dsf/action 'exit "Exit" 'E (lambda nil (dsf/exit)))
    (dsf/cancel-action 'exit)
    (dsf/show-screen)
  )
))

(setq dsf/screen-two (lambda nil
  (block nil
    (dsf/screen 'two "Screen Two")
    (dsf/action 'switch "Switch to One" 'S '(dsf/screen-one))
    ;; etc...
    (dsf/show-screen)
  )
))