Unknown function operation deciphering, exercise in readability by program reasoning

[small Pox]

On Dec 4, 11:37 pm, Madhu <enom... at meer.net> wrote:
> * jvt <5e1f79ab-5432-4f18-b896-362b7406c... at i18g2000yqn.googlegroups.com> :
> Wrote on Sat, 4 Dec 2010 19:34:53 -0800 (PST):
>
> |
> | I think this is correct:
> |
> |
> | (defun unknown-function (sym0)
> |   (let (sym1 sym2)
> |       (while (or sym2 sym0)
> |         (if sym0
> |                 (if (consp sym0)
> |                         (setq sym2 (cons (cdr sym0) sym2) sym0 (car sym0))
> |                       (setq sym3 sym4 (cons sym0 sym1) sym0 nil))
> |               (setq sym0 (car sym2) sym2 (cdr sym2))))
> |       sym1))
> | Thank emacs, not me.
>
> Not quite. You didn't account for the original poster's go-
> ogle masters mangling his message.   But your function appears to be a
> list flattener:

explanation

> (defun unknown-function (list)
>   (let (stack ret)
>     (while (or ret list)
>       (if list
>           (if (consp list)
>               (setq ret (cons (cdr list) ret) ;; hint: this is a push followed by
                      list (car list))          ;;       pop
>             (setq stack (cons list stack)     ;; and so is this
                    list nil))
>         (setq list (car ret) ret (cdr ret))))
>     stack))
>
> ---
> Madhu

I will post an explanation in a few days if no one does this before
since its not urgent for anyone and i have some job assignments to
finish.