From: Tassilo Horn <tassilo@member.fsf.org>
To: Ted Zlatanov <tzz@lifelogs.com>
Cc: emacs-devel@gnu.org
Subject: Re: general lazy list facility for Emacs Lisp?
Date: Wed, 23 Mar 2011 20:10:27 +0100 [thread overview]
Message-ID: <87pqphfyak.fsf@member.fsf.org> (raw)
In-Reply-To: <87tyetfymt.fsf@member.fsf.org> (Tassilo Horn's message of "Wed, 23 Mar 2011 20:03:06 +0100")
Tassilo Horn <tassilo@member.fsf.org> writes:
> I think for "real" memoization, you need clojures. However, I think
> you can simulate memoization with a macro like that (tested only very
> briefly).
>
> (defmacro memoize (name fun)
> (let ((map-name (gensym "memo-map"))
> (args-name (gensym))
> (val-name (gensym)))
> `(progn
> (defvar ,map-name (make-hash-table :test 'equal))
> (defun ,name (&rest ,args-name)
> (let ((,val-name (gethash ,args-name ,map-name)))
> (if ,val-name
> ,val-name
> (puthash ,args-name (apply (quote ,fun) ,args-name)
> ,map-name)))))))
Just a short remark on what I've had in mind with "real" memoization: If
elisp had closures (not clojures ;-)), then one could write memoize as
function, just like the variant in the clojure source code below:
--8<---------------cut here---------------start------------->8---
(defn memoize
[f]
(let [mem (atom {})]
(fn [& args]
(if-let [e (find @mem args)]
(val e)
(let [ret (apply f args)]
(swap! mem assoc args ret)
ret)))))
--8<---------------cut here---------------end--------------->8---
Bye,
Tassilo
next prev parent reply other threads:[~2011-03-23 19:10 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-03-23 15:07 general lazy list facility for Emacs Lisp? Ted Zlatanov
2011-03-23 16:45 ` Tassilo Horn
2011-03-23 17:12 ` Ted Zlatanov
2011-03-23 17:46 ` Thierry Volpiatto
2011-03-23 18:09 ` Ted Zlatanov
2011-03-23 18:27 ` Thierry Volpiatto
2011-03-23 20:33 ` Ted Zlatanov
2011-03-23 20:43 ` Ted Zlatanov
2011-03-23 19:03 ` Tassilo Horn
2011-03-23 19:10 ` Tassilo Horn [this message]
2011-03-23 19:42 ` Ted Zlatanov
2011-03-24 5:27 ` Eric Schulte
2011-03-24 15:43 ` Ted Zlatanov
2011-03-25 12:30 ` Eric Schulte
2011-03-23 20:03 ` Stefan Monnier
2011-03-23 20:14 ` Jason Earl
2011-03-23 20:19 ` Tassilo Horn
2011-03-23 20:18 ` Tassilo Horn
2011-03-23 20:41 ` Tassilo Horn
2011-03-23 21:51 ` Stefan Monnier
2011-03-24 7:26 ` Tassilo Horn
2011-03-23 20:26 ` Ted Zlatanov
2011-03-23 17:13 ` Drew Adams
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