Re: Making alistp matching plistp requirements

On Monday, April 13th, 2026 at 10:55 AM, tpeplt <[email protected]> wrote:

> Heime <[email protected]> writes:
> 
> > On Monday, April 13th, 2026 at 9:59 AM, tpeplt <[email protected]> wrote:
> >
> >>
> >> Here is a simple definition that does not check the contents
> >> of the items in the alist:
> >>
> >>   (defun alistp (obj-list)
> >>     "Determine whether OBJ-LIST is an association list.
> >>      This function definition says that an empty list is not
> >>      an association list."
> >>     (when (and obj-list (proper-list-p obj-list))
> >>       (cl-every #'consp obj-list)))
> >
> > Emacs Lisp plistp allows nil as both keys and values.
> > Have been thinking of keeping with same idea to accept
> > nil.
> >
> 
> That is a simple change to the definition, above:
> 
>   (defun alistp (obj-list)
>     "Determine whether OBJ-LIST is an association list."
>     (when (proper-list-p obj-list)
>       (cl-every #'consp obj-list)))
> 
> Be aware that you may need code to distinguish between a
> value set to nil in an alist and an empty alist:
> 
> (alist-get 'a '((a . nil)))
> ;;=> nil
> (alist-get 'a '())
> ;;=> nil

Have come up with this

(defun lana-alistp (object)
  (declare (pure t) (side-effect-free error-free))
  (cond ((atom object)  (eq object nil))
        (t  (and (consp (car object))
                 (lana-alistp (cdr object))))))

How do you think this compares with your version?
 
> --
> The lyf so short, the craft so long to lerne.
> - Geoffrey Chaucer, The Parliament of Birds.
> 
>