Re: Is this a bug of Emacs-Lisp?

[Luc Teirlinck]

Zhang Wei wrote:

   (defun dummy () '(1 . 2))

   (dummy)
    => (1 . 2)

   (setcdr (dummy) 3)

   (dummy)
    => (1 . 3)

   Modify the return value of dummy changed it's defination. Is this
   a bug of Elisp?

No.  You get the same result in Common Lisp if you replace, in the
above, setcdr with rplacd.

   If it's not. How does this happen?

If a function returns a quoted cons, then after you change the cdr of
the cons, it still returns that (now changed) cons.

Using (defun dummy (cons 1 2)) will prevent this.

Sincerely,

Luc.