;;; Procedure:
;;;   draw-circle!
;;; Parameters:
;;;   image, the image on which we will draw the
;;;          circle
;;;   brush, the brush with which we draw.
;;; Purpose:
;;;   To draw a circle (in some color, at some
;;;     position) using the given brush.
;;; Produces:
;;;   [Nothing]
;;; Preconditions:
;;;   image is a valid image
;;;   brush is a valid brush
;;; Postconditions:
;;;   The image now contains an appealing circle.
(define draw-circle!
  (lambda (image brush)
    (context-set-fgcolor! "red")
    (context-set-brush! brush)
    (image-select-ellipse! image REPLACE 0 0 100 100)
    (image-stroke! image)
    (context-update-displays!)))
       
;;; Procedure:
;;;   sqrt
;;; Parameters:
;;;   n, a real number
;;; Purpose:
;;;   Compute the square root
;;; Produces:
;;;   result, a real number
;;; Preconditions:
;;;   
;;; Postconditions:
;;;   (* result result) is pretty close to n