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Re: Why is FUNC in cl-callf not allowed to be an expression?
From: |
Michael Heerdegen |
Subject: |
Re: Why is FUNC in cl-callf not allowed to be an expression? |
Date: |
Sat, 18 May 2019 00:53:10 +0200 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/27.0.50 (gnu/linux) |
Stefan Monnier <address@hidden> 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.
- Re: Why is FUNC in cl-callf not allowed to be an expression?, (continued)
- Re: Why is FUNC in cl-callf not allowed to be an expression?, Stefan Monnier, 2019/05/16
- Re: Why is FUNC in cl-callf not allowed to be an expression?, Michael Heerdegen, 2019/05/16
- Re: Why is FUNC in cl-callf not allowed to be an expression?, Michael Heerdegen, 2019/05/16
- Re: Why is FUNC in cl-callf not allowed to be an expression?, Stefan Monnier, 2019/05/16
- Re: Why is FUNC in cl-callf not allowed to be an expression?, Michael Heerdegen, 2019/05/16
- Re: Why is FUNC in cl-callf not allowed to be an expression?, Stefan Monnier, 2019/05/16
- Re: Why is FUNC in cl-callf not allowed to be an expression?,
Michael Heerdegen <=
- Re: Why is FUNC in cl-callf not allowed to be an expression?, Stefan Monnier, 2019/05/18
- Re: Why is FUNC in cl-callf not allowed to be an expression?, Michael Heerdegen, 2019/05/20
- Re: Why is FUNC in cl-callf not allowed to be an expression?, Stefan Monnier, 2019/05/20
- Re: Why is FUNC in cl-callf not allowed to be an expression?, Michael Heerdegen, 2019/05/20
- Re: Why is FUNC in cl-callf not allowed to be an expression?, Noam Postavsky, 2019/05/21
- Re: Why is FUNC in cl-callf not allowed to be an expression?, Michael Heerdegen, 2019/05/21
- Re: Why is FUNC in cl-callf not allowed to be an expression?, Stefan Monnier, 2019/05/21
- Re: Why is FUNC in cl-callf not allowed to be an expression?, Andy Moreton, 2019/05/21
- Re: Why is FUNC in cl-callf not allowed to be an expression?, Michael Heerdegen, 2019/05/23
- Re: Why is FUNC in cl-callf not allowed to be an expression?, Michael Heerdegen, 2019/05/21