[plt-scheme] frame:editor problem

Hello, I am having a problem deriving a frame:editor%. When I give it a
canvas that has any init or init-field of it's own. I can see that this
would cause a problem if there was no default value, but this init
has a default value. Further the error message says that the parent
argument (required by editor-canvas%) is not satisfied. Does anyone know
what I'm doing wrong?

-mike

(require (lib "framework.ss" "framework"))

(define mycanvas%
  (class editor-canvas%
    (init (foo #f))
    (super-instantiate ())))

(define myframe%
  (class frame:editor% ()
    (define/override (get-canvas%)
      mycanvas%)
    (define/override (get-editor%)
      pasteboard%)
    (super-instantiate ())))

(instantiate myframe% ())