[racket] Drawing in the Canvas from outside

Hello,

How can I draw the line (for example) in the canvas object defined as:

(define frame (new frame% [label ""] [width 700] [height 500]))
(define canvas (new canvas% [parent frame]
  ;;;; - call from outside:  [paint-callback (lambda (c dc) (send dc
draw-line 1 1 10 10) )]
  ))

by calling a function like

(define (MyDraw canvas-obj) .... (draw-line 1 1 10 10))

?

-- 
Best regards,
Alex
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