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From: Andrea Corallo via "Emacs development discussions." <emacs-devel@gnu.org>
To: Stefan Monnier <monnier@iro.umontreal.ca>
Cc: Zhu Zihao <all_but_last@163.com>, Tomas Hlavaty <tom@logand.com>,
	emacs-devel@gnu.org
Subject: Re: named-let
Date: Mon, 11 Jan 2021 23:28:08 +0000	[thread overview]
Message-ID: <xjfr1mrdpfb.fsf@sdf.org> (raw)
In-Reply-To: <jwvturn3wr3.fsf-monnier+emacs@gnu.org> (Stefan Monnier's message of "Mon, 11 Jan 2021 18:10:17 -0500")

Stefan Monnier <monnier@iro.umontreal.ca> writes:

>>> With the advent of the native-compiler, "all implementations" is even
>>> harder to reach, since it means, interpreter, byte-code, and native code.
>> Well as I mentioned the native compiler is already capable of that if
>> asked, but in general whichever optimization is done by the
>> byte-compiler is picked by the native compiler cause currently the
>> compilation input is LAP.  So I'm not really sure this is adding much
>> complexity from this POV.
>
> All the patches I've seen so far do it in the bytecode interpreter,
> without changing the bytecode itself.

Ah okay, as not said, indeed it should use a goto in bytecode.

> Note that it also depends on what we mean by TCO.
> To me, the "real TCO" is like what Scheme does (so it's not limited to
> recursive functions).  I don't know how easy it is to implement for
> native-comp.  Maybe GCC magically does it for us?

Nope, AFAIU it does it, but not for us (ATM) :)

> [ TCO has also undesirable interactions with debugging/tracing, but
>   I think that would be a secondary concern which should be
>   manageable somehow.  ]

It's also a change in semantic as one must assume that `bar' is not
redefining `foo'.

(defun foo ()
  (bar)
  (foo))

Indeed this does not apply for `named-let' where the scope is lexical
and so you could do the magic :)

>> As a side note I'd be surprised if interpreters in CL implementation are
>> supporting TRE, I guess the interpreter is typically used only for debug
>> or bootstrap therefore should be not very important.  Am I wrong?
>
> I wouldn't know.  But at least for ELisp , it was perceived that
> the plain interpreter is important enough that if it doesn't support TCO
> then we can't write code which relies on TCO, in which case implementing
> TCO in the bytecode interpreter is not very useful.
>
> [ That's part of the reason why I implemented this limited TCO as
>   a macro: it works the same for bytecode as for any other mode of
>   execution so it can really be considered part of the guaranteed
>   semantics rather than a mere optimization.  ]

I see.

Thanks

  Andrea



  reply	other threads:[~2021-01-11 23:28 UTC|newest]

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-09  1:43 named-let Stefan Monnier
2021-01-09  8:58 ` named-let tomas
2021-01-09 16:01   ` named-let Joost Kremers
2021-01-09 21:48     ` named-let Stefan Monnier
2021-01-09 15:23 ` named-let Tomas Hlavaty
2021-01-09 16:44   ` named-let Stefan Monnier
2021-01-09 17:03     ` named-let Helmut Eller
2021-01-09 18:43       ` named-let Stefan Monnier
2021-01-09 18:47     ` named-let Tomas Hlavaty
2021-01-10 18:49   ` named-let Zhu Zihao
2021-01-11 22:27     ` named-let Tomas Hlavaty
2021-01-11 22:36       ` named-let Stefan Monnier
2021-01-11 22:48         ` named-let Tomas Hlavaty
2021-01-11 22:50         ` named-let Andrea Corallo via Emacs development discussions.
2021-01-11 23:10           ` named-let Stefan Monnier
2021-01-11 23:28             ` Andrea Corallo via Emacs development discussions. [this message]
2021-01-11 23:57               ` named-let Stefan Monnier
2021-01-12  9:24                 ` named-let Andrea Corallo via Emacs development discussions.
2021-01-12 18:07                   ` named-let Stefan Monnier
2021-01-12 18:50                     ` named-let Andrea Corallo via Emacs development discussions.
2021-01-12  9:13             ` named-let Helmut Eller
2021-01-13  8:11         ` named-let Zhu Zihao
2021-01-13 14:01           ` named-let Stefan Monnier
2021-01-11 22:40       ` named-let Andrea Corallo via Emacs development discussions.
2021-01-11 22:51         ` named-let Tomas Hlavaty
2021-01-11 23:04           ` named-let Andrea Corallo via Emacs development discussions.
2021-01-12  0:12             ` named-let Tomas Hlavaty
2021-01-20 19:44 ` named-let Stefan Monnier

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