Re: use of mapcan

[Bernt Nilsson <bkn@ida.liu.se>]

> i have a question regarding mapcan used as a filter.  if i want to avoid
> possible problems of side effects can i just return a cons containing
> the value i want to keep?  for example
> (defun x (a) (if (keep a) (cons a nil) nil))
> and
> (mapcan #'x '(a b c d)).
> will this avoid possible problems?
> thanks,
> dan stanger

Yes, the sideeffect of mapcan is limited to the toplevel conses.
But if the thing you want to filter is a sequence, why not use
"remove-if-not"? ex;

	(remove-if-not #'numberp '(a 17 42 b c 97 d e f))

 -- Bernt