bug#75170: add-to-alist: new function

[Eli Zaretskii <eliz@gnu.org>]

> From: Roland Winkler <winkler@gnu.org>
> Cc: 75170@debbugs.gnu.org
> Date: Sun, 29 Dec 2024 08:50:18 -0600
> 
> On Sun, Dec 29 2024, Eli Zaretskii wrote:
> > What is the advantage of adding this function, given that add-to-list
> > can be used with alists, and given that alist-get can nowadays be used
> > as a generalize variable?
> 
> The advantage I see for also having the function add-to-alist is the
> following:
> 
> add-to-list checks for the presence of an element in a list.  In the
> case of alists, this means it checks for the presence of associations.
> You cannot easily modify an existing association with add-to-list.  If
> you have an alist with association (foo . bar) and you call add-to-list
> with an element (foo . baz), add-to-list will not remove the association
> (foo . bar), but the alist will then contain both associations.
> 
> add-to-alist checks for the presence of keys and it makes sure that each
> key appears only once in an alist.  By default, it replaces the value of
> an existing key.  This makes it easy to modify an existing association.
> Only with the optional arg NO-REPLACE non-nil, it will preserve an
> existing association.
> 
> Say, I want in my .emacs file a more complicated association for a key,
> and I do not get initially what I want.  I can call add-to-alist
> multiple times, till I get what I want.
> 
> Is there a simple way to accomplish this in other ways (a way that we
> recommend for users in their init file if they do not want to use
> customize like me)?
> 
> Would it make sense to give this functions a different name if more
> often it may be used to modify existing associations in an alist instead
> of adding new ones?

Let's hear the other co-maintainers.

Stefan and Andrea, WDYT about this?  Should we add this function?