From: Stefan Monnier <monnier@IRO.UMontreal.CA>
To: Paul Pogonyshev <pogonyshev@gmail.com>
Cc: 26073@debbugs.gnu.org
Subject: bug#26073: workaround
Date: Tue, 26 Sep 2017 10:38:36 -0400 [thread overview]
Message-ID: <jwv4lrppozo.fsf-monnier+bug#26073@gnu.org> (raw)
In-Reply-To: <CAG7BpapW7+XUJMuBq2EfbuvYXTN7fP5Fk3geWyphQBJmehbngg@mail.gmail.com> (Paul Pogonyshev's message of "Mon, 20 Mar 2017 10:22:57 +0100")
retitle 26073 How should cl-symbol-macrolet interact with rebindings?
thanks
The problem here is indeed different from the one in bug#26068.
bug#26068 was clearly triggering a (known) bug in cl-symbol-macrolet.
Here it's triggering a (known) misfeature. The source code has the
following comments about it:
;; CL's symbol-macrolet treats re-bindings as candidates for
;; expansion (turning the let into a letf if needed), contrary to
;; Common-Lisp where such re-bindings hide the symbol-macro.
and
;; FIXME: The behavior of CL made sense in a dynamically scoped
;; language, but for lexical scoping, Common-Lisp's behavior might
;; make more sense (and indeed, CL behaves like Common-Lisp w.r.t
;; lexical-let), so maybe we should adjust the behavior based on
;; the use of lexical-binding.
more concretely cl-symbol-macrolet implements the following semantics:
(cl-symbol-macrolet ((x <e>))
... (let ((x <foo>)) ..x..))
=>
... (cl-letf ((<e> <foo>)) ..<e>..)
whereas Common-Lisp's symbol-macrolet wants the following semantics instead:
=> ... (let ((x <foo>)) ..x..)
As mentioned in the comment, it probably makes sense to change
cl-symbol-macrolet in lexical-binding code to follow Common-Lisp's
semantics (tho we'd want to give access to the old semantics if the user
explicitly uses cl-letf).
Not sure what might break if we do that: the main user of
cl-symbol-macrolet outside of generator.el AFAIK is the with-slots of
eieio, so the question is whether some users of with-slots expect
a subsequent `let` binding to temporarily change the slot's value.
I just checked and it seems that no code in Emacs itself relies on this
behavior, so maybe it's "safe" to change it.
Stefan
next prev parent reply other threads:[~2017-09-26 14:38 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-03-12 13:25 bug#26073: bug in generator function with nested dash anaphoric macros Paul Pogonyshev
2017-03-12 14:05 ` bug#26073: Simplified testcase Paul Pogonyshev
2017-03-19 19:31 ` bug#26073: workaround Paul Pogonyshev
2017-03-20 0:49 ` Stefan Monnier
2017-03-20 9:04 ` Paul Pogonyshev
2017-03-20 9:22 ` Paul Pogonyshev
2017-09-26 14:38 ` Stefan Monnier [this message]
2017-09-28 17:18 ` Paul Pogonyshev
2017-09-28 20:07 ` Stefan Monnier
2017-09-28 19:39 ` Philipp Stephani
2017-09-28 20:09 ` Stefan Monnier
2017-11-27 20:34 ` Stefan Monnier
2018-02-09 0:34 ` Noam Postavsky
2018-02-09 2:43 ` Stefan Monnier
2018-02-15 2:37 ` Noam Postavsky
2017-03-20 13:25 ` Stefan Monnier
2017-03-20 14:20 ` Paul Pogonyshev
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