bug#50704: Feature request: Add ensure-list in cl-lib

bug#50704: Feature request: Add ensure-list in cl-lib

[Clément Pit-Claudel]

Hi all,

There are 40+ instances of the following code pattern in Emacs' code base, and many more in packages:

   (if (listp x) x (list x))

It's easy to find single-line instances of it using the regexp [(]if [(]listp .*[(]list .

This pattern is called "ensure-list" in CL:

  (defun ensure-list (thing)
    "Returns THING as a list.

  If THING is already a list (as per listp) it is returned,
  otherwise a one element list containing THING is returned."
    (if (listp thing)
        thing
        (list thing)))

I would like to add a similar function in Emacs, since it comes up so often.  Is that an acceptable change?  

If so:
- Which cl-*.el file should it go into, and where in that file?  
- Should it be a defun or a define-inline?  
- And once it is introduced, should the 40-some instances that could use it be updated, or left as-is?  
- Finally, where should it be documented?

Cheers,
Clément.

bug#50704: Feature request: Add ensure-list in cl-lib

[Lars Ingebrigtsen]

Clément Pit-Claudel <cpitclaudel@gmail.com> writes:

> I would like to add a similar function in Emacs, since it comes up so often.  Is that an acceptable change?  
>
> If so:
> - Which cl-*.el file should it go into, and where in that file?  

I don't think it has to be in cl at all -- we can just call it
`ensure-list'.

> - Should it be a defun or a define-inline?  
> - And once it is introduced, should the 40-some instances that could use it be updated, or left as-is?  
> - Finally, where should it be documented?

defun, depends, and in the list section.  :-)

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

bug#50704: Feature request: Add ensure-list in cl-lib

[Stefan Kangas]

Lars Ingebrigtsen <larsi@gnus.org> writes:

> I don't think it has to be in cl at all -- we can just call it
> `ensure-list'.

+1

>> - And once it is introduced, should the 40-some instances that could use it be updated, or left as-is?

To expand on what Lars said, they can (IMO should) be updated unless
they need to be compatible with old versions of Emacs.

(I would add a comment to the other instances along the lines of "change
to `ensure-list' once Emacs 27.1 compatibility is dropped".)

bug#50704: Feature request: Add ensure-list in cl-lib

[Lars Ingebrigtsen]

Stefan Kangas <stefan@marxist.se> writes:

>> I don't think it has to be in cl at all -- we can just call it
>> `ensure-list'.
>
> +1

I've now added this to Emacs 28.  (And now I'm waiting for complaints
that we should name it `list-ensure' instead.)

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

bug#50704: Feature request: Add ensure-list in cl-lib

[Clément Pit-Claudel]

On 9/21/21 2:31 PM, Lars Ingebrigtsen wrote:
> Stefan Kangas <stefan@marxist.se> writes:
> 
>>> I don't think it has to be in cl at all -- we can just call it
>>> `ensure-list'.
>>
>> +1
> 
> I've now added this to Emacs 28.  (And now I'm waiting for complaints
> that we should name it `list-ensure' instead.)

Nice, thanks a lot!