* bug#73853: 31.0.50; and-let* is useless
@ 2024-10-17 16:27 Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors
2024-10-17 16:40 ` Drew Adams via Bug reports for GNU Emacs, the Swiss army knife of text editors
2024-10-18 2:11 ` Michael Heerdegen via Bug reports for GNU Emacs, the Swiss army knife of text editors
0 siblings, 2 replies; 12+ messages in thread
From: Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors @ 2024-10-17 16:27 UTC (permalink / raw)
To: 73853; +Cc: monnier
Package: Emacs
Version: 31.0.50
According to its docstring, `and-let*` does:
Bind variables according to VARLIST and conditionally evaluate BODY.
Like `when-let*', except if BODY is empty and all the bindings
are non-nil, then the result is the value of the last binding.
IOW the only time it's different from `when-let*` is when BODY is empty,
i.e. its only "feature" compares to `when-let*` is that
(and-let* (..BINDINGS..
(last (binding))))
is equivalent to
(and-let* (..BINDINGS..)
(binding))
Why would anyone write the first instead of the second, other than out
of masochism? Can we kill/deprecate this?
[ I think we have too many (if|when|and)-let(*) for our own good: we
should pick some winners and deprecate the other ones. ]
I could see a use for something called `and-let(*)` but without a BODY,
for the purpose of remove a level of parens and indentation:
(and-let*
(x1 (foo1))
(x2 (foo2)))
i.s.o
(and-let*
((x1 (foo1))
(x2 (foo2))))
- Stefan
^ permalink raw reply [flat|nested] 12+ messages in thread
* bug#73853: 31.0.50; and-let* is useless
2024-10-17 16:27 bug#73853: 31.0.50; and-let* is useless Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors
@ 2024-10-17 16:40 ` Drew Adams via Bug reports for GNU Emacs, the Swiss army knife of text editors
2024-10-18 2:11 ` Michael Heerdegen via Bug reports for GNU Emacs, the Swiss army knife of text editors
1 sibling, 0 replies; 12+ messages in thread
From: Drew Adams via Bug reports for GNU Emacs, the Swiss army knife of text editors @ 2024-10-17 16:40 UTC (permalink / raw)
To: Stefan Monnier, 73853@debbugs.gnu.org
> [ I think we have too many (if|when|and)-let(*) for our own good: we
> should pick some winners and deprecate the other ones. ]
+1.
(Are there really any winners? ;-))
^ permalink raw reply [flat|nested] 12+ messages in thread
* bug#73853: 31.0.50; and-let* is useless
2024-10-17 16:27 bug#73853: 31.0.50; and-let* is useless Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors
2024-10-17 16:40 ` Drew Adams via Bug reports for GNU Emacs, the Swiss army knife of text editors
@ 2024-10-18 2:11 ` Michael Heerdegen via Bug reports for GNU Emacs, the Swiss army knife of text editors
2024-10-18 23:42 ` Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors
2024-10-19 3:38 ` Sean Whitton
1 sibling, 2 replies; 12+ messages in thread
From: Michael Heerdegen via Bug reports for GNU Emacs, the Swiss army knife of text editors @ 2024-10-18 2:11 UTC (permalink / raw)
To: 73853; +Cc: monnier
Stefan Monnier via "Bug reports for GNU Emacs, the Swiss army knife of
text editors" <bug-gnu-emacs@gnu.org> writes:
> Can we kill/deprecate this?
`and-let*'s purpose is to express conditions, `when-let*'s is
conditional evaluation. We have `and-let*' and `when-let*' for the same
reason we have `and' and `when'. See prior discussions.
> [ I think we have too many (if|when|and)-let(*) for our own good: we
> should pick some winners and deprecate the other ones. ]
AFAIR the non-star versions exist for backward compatibility only - so I
would rather get rid of these. Parallel existence of these non-star
vs. star versions should be a temporary state, it complicates the matter
for an epsilon gain.
> I could see a use for something called `and-let(*)` but without a BODY,
> for the purpose of remove a level of parens and indentation:
>
> (and-let*
> (x1 (foo1))
> (x2 (foo2)))
>
> i.s.o
>
> (and-let*
> ((x1 (foo1))
> (x2 (foo2))))
Ugh! - I could not imagine anything with more potential for confusion as
removing the paren around a list of bindings. This would add one more
year-lasting round of discussing these constructs. If you do this,
please call it `and-let*?@!' so than everybody is warned.
Michael.
^ permalink raw reply [flat|nested] 12+ messages in thread
* bug#73853: 31.0.50; and-let* is useless
2024-10-18 2:11 ` Michael Heerdegen via Bug reports for GNU Emacs, the Swiss army knife of text editors
@ 2024-10-18 23:42 ` Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors
2024-10-19 3:50 ` Michael Heerdegen via Bug reports for GNU Emacs, the Swiss army knife of text editors
2024-10-21 7:07 ` Augusto Stoffel
2024-10-19 3:38 ` Sean Whitton
1 sibling, 2 replies; 12+ messages in thread
From: Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors @ 2024-10-18 23:42 UTC (permalink / raw)
To: Michael Heerdegen; +Cc: 73853
>> Can we kill/deprecate this?
> `and-let*'s purpose is to express conditions, `when-let*'s is
> conditional evaluation. We have `and-let*' and `when-let*' for the same
> reason we have `and' and `when'. See prior discussions.
But there isn't the same "historical" support that justifies having
both, and the syntax&semantics of `and-let*` is just weird:
- Why allow a BODY if the motivation is to mirror the normal `and`?
If you want a BODY, use `when-let*`.
- What's the use of the final variable binding since (assuming you
don't use BODY) that variable is never used:
(and-let* ((a (fooa))
(b (foob a))
(i-m-useless (fooc a b))))
- There's a special syntax where the final binding can drop the variable
name (because of the previous point), which makes for an odd syntax
(and-let* ((a (fooa))
(b (foob a))
((weird-call a b))))
So the use with BODY is redundant with `when-let*` and the use without
BODY is quirky (and still redundant with `when-let*`, of course).
>> [ I think we have too many (if|when|and)-let(*) for our own good: we
>> should pick some winners and deprecate the other ones. ]
> AFAIR the non-star versions exist for backward compatibility only - so I
> would rather get rid of these. Parallel existence of these non-star
> vs. star versions should be a temporary state, it complicates the matter
> for an epsilon gain.
100% agreement. Can we `make-obsolete` the non-star versions?
>> I could see a use for something called `and-let(*)` but without a BODY,
>> for the purpose of remove a level of parens and indentation:
>>
>> (and-let*
>> (x1 (foo1))
>> (x2 (foo2)))
>>
>> i.s.o
>>
>> (and-let*
>> ((x1 (foo1))
>> (x2 (foo2))))
>
> Ugh! - I could not imagine anything with more potential for confusion as
> removing the paren around a list of bindings.
FWIW, I agree, I don't like that either.
Stefan
^ permalink raw reply [flat|nested] 12+ messages in thread
* bug#73853: 31.0.50; and-let* is useless
2024-10-18 23:42 ` Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors
@ 2024-10-19 3:50 ` Michael Heerdegen via Bug reports for GNU Emacs, the Swiss army knife of text editors
2024-10-21 7:07 ` Augusto Stoffel
1 sibling, 0 replies; 12+ messages in thread
From: Michael Heerdegen via Bug reports for GNU Emacs, the Swiss army knife of text editors @ 2024-10-19 3:50 UTC (permalink / raw)
To: Stefan Monnier; +Cc: 73853
Stefan Monnier <monnier@iro.umontreal.ca> writes:
> But there isn't the same "historical" support that justifies having
> both, and the syntax&semantics of `and-let*` is just weird:
>
> - Why allow a BODY if the motivation is to mirror the normal `and`?
> If you want a BODY, use `when-let*`.
> - What's the use of the final variable binding since (assuming you
> don't use BODY) that variable is never used:
>
> (and-let* ((a (fooa))
> (b (foob a))
> (i-m-useless (fooc a b))))
One could say BODY _is_ the final condition and therefore it has a
special syntax because it necessarily doesn't need a binding. That way
I've my peace with that syntax.
Anyway, removing `and-let*' would be equally unsatisfying, and
obviously, at least one the two points will remain unless we change
the syntax radically - or remove `and-let*' :-(
> - There's a special syntax where the final binding can drop the variable
> name (because of the previous point), which makes for an odd syntax
>
> (and-let* ((a (fooa))
> (b (foob a))
> ((weird-call a b))))
That I feel too. As an alternative we made the pseudo variable _ work
without compiler warnings. But one gets used to the variable-less
syntax. It's too handy...
> So the use with BODY is redundant with `when-let*` and the use without
> BODY is quirky (and still redundant with `when-let*`, of course).
I see your points, but don't consider them as such a big problem.
Anyway, without having something that is obviously better the discussion
remains quite philosophical. And replacing calls of `and-let*' with
equivalent calls of `when-let*' doesn't make code easier to read, IMO.
> 100% agreement. Can we `make-obsolete` the non-star versions?
I hope we can.
Michael.
^ permalink raw reply [flat|nested] 12+ messages in thread
* bug#73853: 31.0.50; and-let* is useless
2024-10-18 23:42 ` Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors
2024-10-19 3:50 ` Michael Heerdegen via Bug reports for GNU Emacs, the Swiss army knife of text editors
@ 2024-10-21 7:07 ` Augusto Stoffel
2024-10-21 8:57 ` Michael Heerdegen via Bug reports for GNU Emacs, the Swiss army knife of text editors
1 sibling, 1 reply; 12+ messages in thread
From: Augusto Stoffel @ 2024-10-21 7:07 UTC (permalink / raw)
To: 73853; +Cc: michael_heerdegen, monnier
On Fri, 18 Oct 2024 at 19:42, Stefan Monnier via "Bug reports for GNU Emacs, the Swiss army knife of text editors" wrote:
>>> [ I think we have too many (if|when|and)-let(*) for our own good: we
>>> should pick some winners and deprecate the other ones. ]
>> AFAIR the non-star versions exist for backward compatibility only - so I
>> would rather get rid of these. Parallel existence of these non-star
>> vs. star versions should be a temporary state, it complicates the matter
>> for an epsilon gain.
>
> 100% agreement. Can we `make-obsolete` the non-star versions?
Wait... The point of make-obsolete is to generate warning so people
migrate their code, right? So why not warn on the weird
(single-variable binding) use of the non-star version, to eventually
remove that syntax as well as the star variants?
I always type `if-let' because it looks cleaner and saves one indentation
column (which are purely cosmetic reasons), but also I think it would be
weird to have a something* when there's no accompanying something.
>>> I could see a use for something called `and-let(*)` but without a BODY,
>>> for the purpose of remove a level of parens and indentation:
>>>
>>> (and-let*
>>> (x1 (foo1))
>>> (x2 (foo2)))
>>>
>>> i.s.o
>>>
>>> (and-let*
>>> ((x1 (foo1))
>>> (x2 (foo2))))
>>
>> Ugh! - I could not imagine anything with more potential for confusion as
>> removing the paren around a list of bindings.
>
> FWIW, I agree, I don't like that either.
Sure, I guess nobody wants that, but this idea is getting closer to a
`thread-while' macro (variation of `thread-as') which I still maintain
would be really handy (much more so than the existing ones, which are
limited by the inconsistency of the argument ordering in Elisp).
^ permalink raw reply [flat|nested] 12+ messages in thread
* bug#73853: 31.0.50; and-let* is useless
2024-10-21 7:07 ` Augusto Stoffel
@ 2024-10-21 8:57 ` Michael Heerdegen via Bug reports for GNU Emacs, the Swiss army knife of text editors
2024-10-21 12:09 ` Sean Whitton
0 siblings, 1 reply; 12+ messages in thread
From: Michael Heerdegen via Bug reports for GNU Emacs, the Swiss army knife of text editors @ 2024-10-21 8:57 UTC (permalink / raw)
To: Augusto Stoffel; +Cc: 73853, monnier
Augusto Stoffel <arstoffel@gmail.com> writes:
> I always type `if-let' because it looks cleaner and saves one indentation
> column (which are purely cosmetic reasons), but also I think it would be
> weird to have a something* when there's no accompanying something.
Good point, we should decide which names to use. Personally i prefer
the names ending with star, because bindings are not parallel as in
`let'. But we also already spoke about this. Dunno which names are
more popular, it's a matter of taste.
Michael.
^ permalink raw reply [flat|nested] 12+ messages in thread
* bug#73853: 31.0.50; and-let* is useless
2024-10-21 8:57 ` Michael Heerdegen via Bug reports for GNU Emacs, the Swiss army knife of text editors
@ 2024-10-21 12:09 ` Sean Whitton
0 siblings, 0 replies; 12+ messages in thread
From: Sean Whitton @ 2024-10-21 12:09 UTC (permalink / raw)
To: Augusto Stoffel; +Cc: Michael Heerdegen, 73853, monnier
Hello,
On Mon 21 Oct 2024 at 10:57am +02, Michael Heerdegen via "Bug reports for GNU Emacs, the Swiss army knife of text editors" wrote:
> Augusto Stoffel <arstoffel@gmail.com> writes:
>
>> I always type `if-let' because it looks cleaner and saves one indentation
>> column (which are purely cosmetic reasons), but also I think it would be
>> weird to have a something* when there's no accompanying something.
>
> Good point, we should decide which names to use. Personally i prefer
> the names ending with star, because bindings are not parallel as in
> `let'. But we also already spoke about this. Dunno which names are
> more popular, it's a matter of taste.
I prefer if-let* for this reason too. Also:
- it informs a reader that there is no way they are going to see the
unusual single binding syntax.
- Common Lisp's ubiquitous Alexandria library of basic utilities has an
if-let which has the unusual single binding syntax. In fact, that is
probably where our if-let came from. So if we are moving away from
that, it makes sense to use a different name for the thing we
invented -- if-let*.
--
Sean Whitton
^ permalink raw reply [flat|nested] 12+ messages in thread
* bug#73853: 31.0.50; and-let* is useless
2024-10-18 2:11 ` Michael Heerdegen via Bug reports for GNU Emacs, the Swiss army knife of text editors
2024-10-18 23:42 ` Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors
@ 2024-10-19 3:38 ` Sean Whitton
2024-10-20 12:24 ` Stefan Kangas
1 sibling, 1 reply; 12+ messages in thread
From: Sean Whitton @ 2024-10-19 3:38 UTC (permalink / raw)
To: 73853; +Cc: Michael Heerdegen, monnier
Hello,
On Fri 18 Oct 2024 at 04:11am +02, Michael Heerdegen via "Bug reports for GNU Emacs, the Swiss army knife of text editors" wrote:
> `and-let*'s purpose is to express conditions, `when-let*'s is
> conditional evaluation. We have `and-let*' and `when-let*' for the
> same reason we have `and' and `when'. See prior discussions.
Right. The Lisp convention of using `when' for pure control flow and
`and' for returning values is a good aid to readability.
If we don't have and-let*, then we can't use this convention in the case
that we also want to bind variables.
So, I am very keen for and-let* to remain.
>> [ I think we have too many (if|when|and)-let(*) for our own good: we
>> should pick some winners and deprecate the other ones. ]
>
> AFAIR the non-star versions exist for backward compatibility only - so
> I would rather get rid of these. Parallel existence of these non-star
> vs. star versions should be a temporary state, it complicates the
> matter for an epsilon gain.
Yes. I would like us to move forward with removing the non-star ones.
I believe there was a previous attempt to deprecate them but it had to
be backed out. But maybe now is the time to try again.
--
Sean Whitton
^ permalink raw reply [flat|nested] 12+ messages in thread
* bug#73853: 31.0.50; and-let* is useless
2024-10-19 3:38 ` Sean Whitton
@ 2024-10-20 12:24 ` Stefan Kangas
2024-10-22 14:47 ` bug#73853: 31.0.50; Should and-let* become a synonym for when-let*? Sean Whitton
0 siblings, 1 reply; 12+ messages in thread
From: Stefan Kangas @ 2024-10-20 12:24 UTC (permalink / raw)
To: Sean Whitton, 73853; +Cc: Michael Heerdegen, monnier
Sean Whitton <spwhitton@spwhitton.name> writes:
> I would like us to move forward with removing the non-star ones.
I also agree that removing them would make sense.
^ permalink raw reply [flat|nested] 12+ messages in thread
* bug#73853: 31.0.50; Should and-let* become a synonym for when-let*?
2024-10-20 12:24 ` Stefan Kangas
@ 2024-10-22 14:47 ` Sean Whitton
2024-10-22 15:24 ` Michael Heerdegen via Bug reports for GNU Emacs, the Swiss army knife of text editors
0 siblings, 1 reply; 12+ messages in thread
From: Sean Whitton @ 2024-10-22 14:47 UTC (permalink / raw)
To: Stefan Kangas, Michael Heerdegen, monnier; +Cc: control, 73853
retitle 73853 Should and-let* become a synonym for when-let*?
thanks
Hello,
On Sun 20 Oct 2024 at 05:24am -07, Stefan Kangas wrote:
> Sean Whitton <spwhitton@spwhitton.name> writes:
>
>> I would like us to move forward with removing the non-star ones.
>
> I also agree that removing them would make sense.
I've found the old discussion on this:
- https://debbugs.gnu.org/cgi/bugreport.cgi?bug=60758#58
- https://lists.gnu.org/archive/html/emacs-devel/2018-03/msg00052.html
- https://lists.gnu.org/archive/html/emacs-devel/2018-03/msg00219.html
Based on my reading of this thread and those old discussions, I conclude
- it is fine to mark when-let and if-let as obsolete for Emacs 31, and
generally there's more of a consensus, and several good reasons, to do
that instead of removing if-let* and when-let*
- I'd like to go ahead and install a patch marking when-let and if-let
as obsolete, unless Michael is keen to be the one to do it as the
initiator of the previous effort
- enough people want to keep and-let*, but possibly some aspects of its
syntax should be removed
- I'm retitling the bug to reflect that.
--
Sean Whitton
^ permalink raw reply [flat|nested] 12+ messages in thread
* bug#73853: 31.0.50; Should and-let* become a synonym for when-let*?
2024-10-22 14:47 ` bug#73853: 31.0.50; Should and-let* become a synonym for when-let*? Sean Whitton
@ 2024-10-22 15:24 ` Michael Heerdegen via Bug reports for GNU Emacs, the Swiss army knife of text editors
0 siblings, 0 replies; 12+ messages in thread
From: Michael Heerdegen via Bug reports for GNU Emacs, the Swiss army knife of text editors @ 2024-10-22 15:24 UTC (permalink / raw)
To: Sean Whitton; +Cc: 73853, control, Stefan Kangas, monnier
Sean Whitton <spwhitton@spwhitton.name> writes:
> retitle 73853 Should and-let* become a synonym for when-let*?
> thanks
Thanks for the fine summary.
> - I'd like to go ahead and install a patch marking when-let and if-let
> as obsolete, unless Michael is keen to be the one to do it as the
> initiator of the previous effort
He is not, feel free to go ahead when there are no objections from
others.
Michael.
^ permalink raw reply [flat|nested] 12+ messages in thread
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2024-10-17 16:27 bug#73853: 31.0.50; and-let* is useless Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors
2024-10-17 16:40 ` Drew Adams via Bug reports for GNU Emacs, the Swiss army knife of text editors
2024-10-18 2:11 ` Michael Heerdegen via Bug reports for GNU Emacs, the Swiss army knife of text editors
2024-10-18 23:42 ` Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors
2024-10-19 3:50 ` Michael Heerdegen via Bug reports for GNU Emacs, the Swiss army knife of text editors
2024-10-21 7:07 ` Augusto Stoffel
2024-10-21 8:57 ` Michael Heerdegen via Bug reports for GNU Emacs, the Swiss army knife of text editors
2024-10-21 12:09 ` Sean Whitton
2024-10-19 3:38 ` Sean Whitton
2024-10-20 12:24 ` Stefan Kangas
2024-10-22 14:47 ` bug#73853: 31.0.50; Should and-let* become a synonym for when-let*? Sean Whitton
2024-10-22 15:24 ` Michael Heerdegen via Bug reports for GNU Emacs, the Swiss army knife of text editors
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