Re: Is this a bug of Emacs-Lisp?

[David Kastrup]

Zhang Wei <address@hidden> writes:

> (defun dummy () '(1 . 2))
>
> (dummy)
>  => (1 . 2)
>
> (setcdr (dummy) 3)
>
> (dummy)
>  => (1 . 3)
>
> Modify the return value of dummy changed it's defination.

No, it didn't.

> Is this a bug of Elisp? If it's not. How does this happen?

'(1 . 2) is a cons cell.  Cons cells are _always_ accessed by
reference, like arrays and strings.

So what is compiled into the function is a reference to a cons cell,
and this reference stays the same.  setcdr however changes the cons
cell itself.

-- 
David Kastrup, Kriemhildstr. 15, 44793 Bochum