From: "Pierre L. Nageoire" <devel@pollock-nageoire.net>
To: Stefan Monnier <monnier@iro.umontreal.ca>
Cc: 56596@debbugs.gnu.org, Lars Ingebrigtsen <larsi@gnus.org>
Subject: bug#56596: 29.0.50; void-variable cl--nm
Date: Mon, 18 Jul 2022 05:36:11 +0200 [thread overview]
Message-ID: <871quj6qj8.fsf@pollock-nageoire.net> (raw)
In-Reply-To: <jwv4jzgd5rs.fsf-monnier+emacs@gnu.org> (Stefan Monnier's message of "Sat, 16 Jul 2022 19:19:41 -0400")
Hi Stefan,
Thanks for these detailed explanations; I think I will be able to
modify my codes to make them work with this new cl-generic
implementation.
Best regards
Stefan Monnier <monnier@iro.umontreal.ca> writes:
>>> I can reproduce this -- but only when using dynamic binding. When using
>>> lexical binding, things work fine.
>
> Indeed, `cl-defmethod` (and `cl-defgeneric`) aren't guaranteed to work in
> dynbind code. They often do, admittedly.
>
>>> I've added Stefan to the CCs; perhaps he has some comments.
>>
>> I suspect that cl-generic implementation has recently changed and that
>> it should not be used nowadays exactly like it has been. Any small
>> explanations from Stefan would be greatly appreciated !
>
> The "next method" is not known when we compile `cl-defmethod` but it is
> known when we build the "effective method", which is expected to be done
> much less often than actual calls to that method.
>
> The old code for `cl-defmethod` turned
>
> (cl-defmethod I ((d raw-daughter))
> (format "the daughter of %s"
> (cl-call-next-method)))
>
> into something like
>
> (cl-..register (raw-daughter)
> (lambda (cnm d)
> (format "the daughter of %s"
> (apply cnm))))
>
> forcing the caller to build a `cnm` closure which captures the args list
> containing the value of the `d` argument. Also it made it difficult to
> implement `next-method-p` since that requires digging into this `cnm`
> closure to see if it's one of those that would signal no-next-method.
>
> The new code instead is a bit like:
>
> (cl-..register (raw-daughter)
> (lambda (nm)
> (lambda (&rest args)
> (let ((cnm (lambda (&rest cnmargs) (apply nm (or cnmargs args)))))
> (destructive-bind (d) args
> (format "the daughter of %s"
> (apply cnm)))))))
>
> This basically moves some of the code from the caller to here, which
> doesn't seem to buy us very much but:
> - it makes it much easier to implement `next-method-p` because now we
> have access to the actual "next method", rather than to a closure that
> combines the next methods with the saved arg list, so it's much easier
> to tell if the next method is the one that signals no-next-method.
> - we occasionally get to skip building the `cnm` closure because we can
> use λ-lifting instead (basically the byte-compiler gets to see both
> parts of the code together and can thus change it: with this new code
> we could actually improve the code generated by the byte-compiler
> even further).
>
> Problem is that the new code relies on the use of currying (see how
> `nm` and `args` are now passed in a curried fashion), which is only
> possible with lexical scoping.
>
>
> Stefan
next prev parent reply other threads:[~2022-07-18 3:36 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-07-16 8:46 bug#56596: 29.0.50; void-variable cl--nm Pierre L. Nageoire
2022-07-16 11:12 ` Lars Ingebrigtsen
2022-07-16 18:06 ` Pierre L. Nageoire
2022-07-16 23:19 ` Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors
2022-07-18 3:36 ` Pierre L. Nageoire [this message]
2022-07-16 22:42 ` Stefan Kangas
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