Re: Check whether an object is an alist

[Heime <heimeborgia@protonmail.com>]

On Wednesday, September 18th, 2024 at 1:58 AM, tomas@tuxteam.de <tomas@tuxteam.de> wrote:

> On Tue, Sep 17, 2024 at 01:51:54PM +0000, Heime wrote:
> 
> [...]
> 
> > Have modified the code to this
> > 
> > (defun torium-alist-p (obj)
> > "Return t if object OBJ is an association list (alist)."
> > (and (listp obj)
> > (every (lambda (x)
> > (or (null x)
> > (consp x)))
> > obj)))
> > 
> > I want to allow empty lists and empty keys. Or should I remove (null x)
> > as well ?
> 
> 
> That depends on how strict you want to be. Have you read elisp's
> docs on association lists?
> 
> Elisp tends to tolerate alists whose elements are not pairs. Other
> Lisps are stricter. Your function is a funny in-between (nil non-pairs
> are OK, but others are not).
> 
> First try to understand what you are trying to do, then do. Note that,
> contrary to hashes, alists are not strictly defined.
> 
> Cheers
> --
> t

Originally I tried to find something as alistp but did not find any.  I would
have stayed to what it would have allowed.  But then I started writing my own.
For what I am doing, there is always a key and value in each cell.  

But taking in consideration what others have been saying here about alists, I 
decided to be more flexible and allow empty alists and keys with nil.  Then
(null x) should not be there because it allows nil non-pairs.


This is what I am trying to do with

(defun torium-alist-p (obj)
  "Return t if object OBJ is an association list (alist).  An alist 
can be empty and nil can act as a key."
  (and (listp obj)
       (every (lambda (x)
                (or (null x)
                (consp x)))
              obj)))