Re: Making alistp matching plistp requirements

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

-- 
The lyf so short, the craft so long to lerne.
- Geoffrey Chaucer, The Parliament of Birds.