Part 5: Control flow clogged

[chuchana]

When clicking, the printing doesn't seem to finish correctly, e.g. for this snippet:

(defun hello-private (body)
  "Create a div on new pages containing - hello world
That when clicked changes color."
  (set-on-click (create-div body :content "hello world")
                (lambda (obj)
                  (setf (color obj) (progn
                                      (terpri)
                                      (princ "Setting color to:")
                                      (print (rgb (random 255)
                                                  (random 255)
                                                  (random 255))))))))

Instead of

Setting color to:
"rgb(...)"

Setting color to:
"rgb(...)"

Setting color to:
"rgb(...)"

I get

Setting color to:

"rgb(...)"
Setting color to:

"rgb(...)"
Setting color to:

(empty lines added for clarity)

---

Since I could not imagine that I found a bug in progn, I searched the web for a while and found a similar problem and answer.

Adding (finish-output) to the function fixes the problem:

(defun hello-private (body)
  "Create a div on new pages containing - hello world
That when clicked changes color."
  (set-on-click (create-div body :content "hello world")
                (lambda (obj)
                  (setf (color obj) (progn
                                      (terpri)
                                      (princ "Setting color to:")
                                      (print (rgb (random 255)
                                                  (random 255)
                                                  (random 255)))
                                      (finish-output))))))

The same applies to the next variation of hello-private:

(defun hello-private (body)
  "Create a div on new pages containing - hello world
That when clicked changes color."
  (set-on-click (create-div body :content "CLICK ME TO PLAY")
                (lambda (obj)
                  (setf (color obj) (cond ((equal (random 10) 1)
                                           (setf (text obj) "--(O)-(O)--")
                                           (print "RED LIGHT!")
                                           (finish-output)
                                           (rgb 255 0 0))
                                          (t
                                           (setf (text obj) "--(X)-(X)--")
                                           (print "I'm not looking..")
                                           (finish-output)
                                           (rgb 0
                                                (random 255)
                                                (random 255))))))))