Is it possible to display bitmap in a loop?

[drakbar]

I am drawing bitmaps to the output like so

#lang racket

(require racket/draw)  

(define imageWidth 64)
(define imageHeight 64)

(define target (make-bitmap imageWidth imageHeight)) 
(define dc (new bitmap-dc% [bitmap target]))

(define (set-frame dc color)
  (send dc set-pen "black" 2 'solid)
  (send dc set-brush color 'solid)
)

(define (display-frame dc)
  (send dc draw-rectangle 0 0 imageWidth imageHeight)
  target
)

(set-frame dc (make-color 255 255 255))
(display-frame dc)

(set-frame dc (make-color 255 0 0))
(display-frame dc)

(set-frame dc (make-color 0 255 0))
(display-frame dc)

(set-frame dc (make-color 0 0 255))
(display-frame dc)

However if I try to loop and send the bitmap to the output like so I don't see anything

#lang racket

(require racket/draw)  

(define imageWidth 64)
(define imageHeight 64)

(define target (make-bitmap imageWidth imageHeight)) 
(define dc (new bitmap-dc% [bitmap target]))

(define (set-frame dc color)
  (send dc set-pen "black" 2 'solid)
  (send dc set-brush color 'solid)
)

(define (display-frame dc)
  (send dc draw-rectangle 0 0 imageWidth imageHeight)
  target
)

(for ([x (in-range 4)])
    (set-frame dc (make-color 255 0 0))
    (display-frame dc)
)

I am not sure why its not working, but I am sure I am just making some noobie mistake.

[gus-massa]

The result of display-frame is a bitmap% object. The results of each top expression have an implicit println, so the first example,

(println (set-frame dc (make-color 255 255 255))) ; --> (println (void)) doen't show anything
(println (display-frame dc)) ; --> shows a square

The expressions inside for or any other construction don't have the implicit println. So in the second example

(for ([x (in-range 4)])
    (set-frame dc (make-color 255 0 0)) ; --> not shown
    (display-frame dc); --> not shown
) ; --> the result of for is (void), so --> (println (void)) doen't show anything