bug#50929: Add slurp-sexp and barf-sexp

[Juri Linkov <juri@linkov.net>]

>>>> I'd like to suggest adding the command slurp-sexp and barf-sexp to
>>>> lisp.el (perhaps after changing the names). These commands were
>>>> popularized by structural editing packages like Paredit, and allow the
>>>> user to quickly pull or push s-expressions into the current list.
>>>
>>> There's already paredit-forward-slurp-sexp (etc) -- do we need them in
>>> lisp.el, too?
>>
>> Need is a difficult concept: Paredit also has a raise-sexp analogue, so
>> lisp.el doesn't need that either (hence why I added slurp-sexp and
>> barf-sexp right under raise-sexp), beyond the fact that it has already
>> been added to the file.
>
> I rather think that raise-sexp is an indication that these commands do
> not belong in Emacs core -- it seems like raise-sexp was added in 2004,
> but nobody seems to have clamoured for getting a key binding for it,
> which would be unusual if it was a popular command.  (And nobody has
> documented it either, apparently.)

I use raise-sexp all the time bound to 'C-x C-M-u'
with mnemonics of "delete everything except sexp raised by C-M-u".
(I don't know if this will make sense for ‘lisp.el’.)

> My feeling is that these commands are vital for people who do structural
> editing a lot -- but those people use paredit or similar.  People who
> don't really don't think in those terms, so they don't miss the commands.
>
> So my conclusion is that we don't want to add these commands, so I'm
> closing this bug report (but if everybody else feels strongly that Emacs
> should grow a more substantial support for structural Lisp editing, I
> won't protest, but it should be just that -- more substantial, with a
> fuller set of commands (with better names) and an Emacs manual section
> explaining how it all ties together).

Sorry, I don't have an opinion about the proposed new commands:
it seems easier to use mark-sexp/copy/paste for complex structural editing
than to remember all possible list transformation commands with their keybindings.
But more commands could be added if more people will ask for them.