Barry Margolin wrote:

> In article <2...@esosun.UUCP> jack...@esosun.UUCP (Jerry Jackson) writes:
> >(defmacro dolist ((var list &optional result-form) &rest body)
> > (let ((listvar (gensym)))
> > `(do* ((,listvar ,list (cdr ,listvar))
> > (,var (car ,list) (car ,listvar)))
> > ((null ,listvar) ,result-form)
> > ,@body)))
>
> Both versions of your macro have a bug: they have ",list" in two
> places in the expansion. This will cause the list expression to be
> evaluated twice, which could cause problems if it has side effects.
> In the above case, both the second line of the DO* form should be
>
> (,var (car ,listvar) (car ,listvar))
>
> Fixing the DO version is slightly more complicated.

Scheme

(define-syntax dolist
(syntax-rules ()
[(dolist (var list result-form ...) expr ...)
(do ((listvar list (cdr listvar))
(var #f))
((null? listvar) result-form ...)
(set! var (car listvar))
expr ...)]))