From: Ivan Kanis <ivan.kanis@googlemail.com>
To: Stefan Monnier <monnier@IRO.UMontreal.CA>
Cc: emacs devel <emacs-devel@gnu.org>
Subject: Re: defining a setter function with gv.el
Date: Thu, 30 Aug 2012 18:05:07 +0200 [thread overview]
Message-ID: <87obls1i30.fsf@kanis.fr> (raw)
In-Reply-To: <jwvharo6r9e.fsf-monnier+emacs@gnu.org> (Stefan Monnier's message of "Mon, 27 Aug 2012 16:28:32 -0400")
Hi Stefan,
As I was trying to make sense of it I tried the following in my
*scratch* buffer:
(setq lexical-binding t)
(defun alist-get (key alist)
"Get the value associated to KEY in ALIST."
(declare
(gv-expander
(lambda (do)
(macroexp-let2 macroexp-copyable-p k key
(gv-letplace (getter setter) alist
(macroexp-let2 nil p `(assoc ,k ,getter)
(funcall do `(cdr ,p)
(lambda (v)
`(if ,p (setcdr ,p ,v)
,(funcall setter
`(cons (cons ,k ,v) ,getter))))))))))))
(setq foo '((bar . foo) (baz . qux)))
(alist-get 'bar foo) => "Get the value associated to KEY in ALIST."
It's as if everything in declare was not evaluated. Where did I err?
Stefan Monnier <monnier@IRO.UMontreal.CA> wrote:
> and the code we want to generate for a `setf' is along the lines of:
>
> (let* ((k KEY)
> (a ALIST)
> (p (assoc k (alist-getter a)))
> (v VAL))
> (if p (setcdr p v)
> (alist-setter a (cons (cons k v) (alist-getter a)))))
Yes this is what needs to be generated. I don't understand why there
are two lambdas in alist-get. There is no map type function so I don't
understand what they do.
Is there any chance you would uncomment this function so that I can use
it in my code?
Take care,
--
Ivan Kanis
http://ivan.kanis.fr
History is a gallery of pictures in which there are few original and
many copies.
-- Alexis de Tocqueville
next prev parent reply other threads:[~2012-08-30 16:05 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-08-27 5:56 defining a setter function with gv.el Ivan Kanis
2012-08-27 12:54 ` Stefan Monnier
2012-08-27 18:10 ` Ivan Kanis
2012-08-27 20:28 ` Stefan Monnier
2012-08-30 16:05 ` Ivan Kanis [this message]
2012-08-31 0:59 ` Stefan Monnier
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