From: Michael Heerdegen <michael_heerdegen@web.de>
To: Stefan Monnier <monnier@iro.umontreal.ca>
Cc: emacs-devel@gnu.org
Subject: Re: Why is FUNC in cl-callf not allowed to be an expression?
Date: Sat, 18 May 2019 00:53:10 +0200 [thread overview]
Message-ID: <87tvdshew9.fsf@web.de> (raw)
In-Reply-To: <jwvbm02dmru.fsf-monnier+emacs@gnu.org> (Stefan Monnier's message of "Thu, 16 May 2019 19:06:55 -0400")
Stefan Monnier <monnier@iro.umontreal.ca> writes:
> So I think it needs a name which clarifies the difference.
Hmm, ok. Here is a draft supporting multiple (parallel) bindings. The
macro builds code by recursively calling `gv-letplace', the innermost
expression is one big symbol-macrolet that makes use of the bound
getters and setters.
#+begin_src emacs-lisp
(defmacro gv-place-bind (bindings &rest body)
"Make place expression bindings.
BINDINGS is a list of elements of the form (VAR PLACE).
Eval BODY with...
The effect is very similar to `cl-symbol-macrolet'
but preferred for place expressions since it produces more
efficient code.
\(fn ((VAR PLACE) ...) FORM...)"
(declare (indent 1))
(letrec ((helper
(lambda (bindings symbols+getters+setters body)
(if bindings
(let ((binding (car bindings)))
(gv-letplace (getter setter) (cadr binding)
(funcall helper
(cdr bindings)
(cons (list (car binding) getter setter)
symbols+getters+setters)
body)))
`(cl-symbol-macrolet
,(mapcar
(lambda (entry)
`(,(car entry)
(gv-synthetic-place ,(cadr entry) ,(caddr entry))))
(nreverse symbols+getters+setters))
,@body)))))
(funcall helper bindings '() body)))
#+end_src
;; Example:
(let ((l '(2 3 4)))
(gv-place-bind ((p (cdr l)))
(unless (memq 1 p)
(setf p (cons 1 p))))
l)
;; ==> (2 1 3 4)
Writing the docstring made me thoughtful though - how is this different
from symbol-macrolet? An advantage is that it generates a bit more
efficient code for "complicated" (nested) place expressions.
OTOH, the purpose of symbol-macrolet is, at the end, more or less
defining abbreviations of place expressions. So I wonder now if the
right thing to do is rather to improve symbol-macrolet instead to make
it generate better code by consulting getters and setters itself,
instead of blindly substituting.
My second point in this message: thinking once more about callf, we
could also support a syntax like (callf (with EXPR) PLACE ARG) or
something like that to support expressions as first arg.
Michael.
next prev parent reply other threads:[~2019-05-17 22:53 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-09 21:52 Why is FUNC in cl-callf not allowed to be an expression? Michael Heerdegen
2019-05-10 0:47 ` Stefan Monnier
2019-05-10 11:32 ` Michael Heerdegen
2019-05-10 13:28 ` Stefan Monnier
2019-05-10 14:19 ` Stefan Monnier
2019-05-10 14:22 ` Stefan Monnier
2019-05-10 15:18 ` Michael Heerdegen
2019-05-13 16:47 ` Stefan Monnier
2019-05-14 12:36 ` Michael Heerdegen
2019-05-14 23:32 ` Michael Heerdegen
2019-05-15 2:02 ` Stefan Monnier
2019-05-15 16:38 ` Michael Heerdegen
2019-05-15 17:19 ` Michael Heerdegen
2019-05-16 2:18 ` Michael Heerdegen
2019-05-16 13:12 ` Stefan Monnier
2019-05-16 14:37 ` Michael Heerdegen
2019-05-16 15:09 ` Michael Heerdegen
2019-05-16 19:34 ` Stefan Monnier
2019-05-16 21:46 ` Michael Heerdegen
2019-05-16 23:06 ` Stefan Monnier
2019-05-17 22:53 ` Michael Heerdegen [this message]
2019-05-18 14:09 ` Stefan Monnier
2019-05-20 23:25 ` Michael Heerdegen
2019-05-21 2:01 ` Stefan Monnier
2019-05-21 2:47 ` Michael Heerdegen
2019-05-21 10:16 ` Noam Postavsky
2019-05-21 16:38 ` Michael Heerdegen
2019-05-21 17:38 ` Stefan Monnier
2019-05-21 7:26 ` Andy Moreton
2019-05-23 23:02 ` Michael Heerdegen
2019-05-22 1:00 ` Michael Heerdegen
2019-05-23 1:50 ` Michael Heerdegen
2019-05-23 3:38 ` Stefan Monnier
2019-05-23 23:38 ` Michael Heerdegen
2019-05-24 15:29 ` Stefan Monnier
2019-05-28 19:54 ` Michael Heerdegen
2019-05-27 0:20 ` Michael Heerdegen
2019-05-29 17:02 ` Stefan Monnier
2019-05-15 19:17 ` Michael Heerdegen
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