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Re: Use the new let-opt macro in place of pcase-let in lisp-mode.el
From: |
Oleh Krehel |
Subject: |
Re: Use the new let-opt macro in place of pcase-let in lisp-mode.el |
Date: |
Mon, 18 May 2015 19:26:29 +0200 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/25.0.50 (gnu/linux) |
Stefan Monnier <address@hidden> writes:
>> (defmacro let-opt (bindings &rest body)
>> "Like `let', but allows for compile time optimization.
>> Expressions wrapped with `opt' will be subsituted for their values.
>> \n(fn BINDINGS BODY)"
>> (declare (indent 1) (debug let))
>> (let ((bnd (mapcar (lambda (x) (cons (car x) (eval (cadr x))))
>> bindings)))
>> `(cl-macrolet ((opt (&rest body)
>> (list 'quote (eval (cons 'progn body) ',bnd))))
>> ,@body)))
>
> I think I like this idea of "compile-time-only let-binding".
> But I don't like this `opt' thingy very much and I think we can get rid
> of it if we use dynamic-scoping instead.
>
> IOW, define a let-when-compile macro which uses progv to setup the
> bindings and then calls `macroexpand-all' on the body. The body's
> `eval-when-compile' can then use those vars just fine.
I wrote this:
(defmacro let-when-compile (bindings &rest body)
"Like `let', but allows for compile time optimization.
\n(fn BINDINGS BODY)"
(declare (indent 1) (debug let))
`(progv ',(mapcar #'car bindings)
',(mapcar (lambda (x) (eval (cadr x))) bindings)
,@body))
It sort of works (evals to the correct thing, and the byte code looks
OK), but I get a lot of byte compiler warnings. And I don't see while
`progv' should expand to a `while' loop. Anyway, here's an example:
(let-when-compile ((foo (+ 2 2)))
(defvar bar (+ foo foo)))
And here's the expansion, after I've evaluated the while loop:
(eval
(let ((foo (quote 4)))
(funcall
(quote
(lambda nil
(defvar bar (+ foo foo)))))))
On the other hand, using `let-opt':
(let-opt ((foo (+ 2 2)))
(defvar bar (opt (+ foo foo))))
expands to this:
(defvar bar '8)
Which I think could be valuable while refactoring.
Oleh
- Use the new let-opt macro in place of pcase-let in lisp-mode.el, Oleh Krehel, 2015/05/18
- Re: Use the new let-opt macro in place of pcase-let in lisp-mode.el, Stefan Monnier, 2015/05/18
- Re: Use the new let-opt macro in place of pcase-let in lisp-mode.el,
Oleh Krehel <=
- Re: Use the new let-opt macro in place of pcase-let in lisp-mode.el, Stefan Monnier, 2015/05/18
- Re: Use the new let-opt macro in place of pcase-let in lisp-mode.el, Oleh Krehel, 2015/05/19
- Re: Use the new let-opt macro in place of pcase-let in lisp-mode.el, Stefan Monnier, 2015/05/19
- Re: Use the new let-opt macro in place of pcase-let in lisp-mode.el, Oleh Krehel, 2015/05/20
- Re: Use the new let-opt macro in place of pcase-let in lisp-mode.el, Stefan Monnier, 2015/05/20
- Re: Use the new let-opt macro in place of pcase-let in lisp-mode.el, Oleh Krehel, 2015/05/20
- Re: Use the new let-opt macro in place of pcase-let in lisp-mode.el, Stefan Monnier, 2015/05/20