`while` is hanging

Question

    (defun test (n)
      (let ((list1 ()))
        (while (< (length list1) 10))
        (push (random n) list1)
        list1))

I'm trying to add (random n) to list1 while the length of list1 is less than 10. When I evaluate this function, it hangs. What am I doing wrong?

Answer 1

You closed your while loop before doing the push. So the list length stayed less than 10.

(defun test (n)
  (let ((list1 ()))
    (while (< (length list1) 10)
      (push (random n) list1))
    list1))

Moral: Indent your code properly. C-M-q is your friend, as is TAB. See the Emacs manual, node Indenting Several Lines.

Hanging should have been your clue that the while loop was infinite. That would tell you that the list length wasn't increasing.