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From: | Ken Raeburn |
Subject: | Re: Elisp flet construct |
Date: | Thu, 23 Jul 2009 17:53:21 -0400 |
On Jul 23, 2009, at 16:46, Andy Wingo wrote:
On Tue 21 Jul 2009 15:10, Daniel Kraft <address@hidden> writes:Just a little addition to the subject of extensions: I'd very much liketo add lexical-let and lexical-let* as another set of extensions, because this gives the possibility to use "fast" lexical variables without the dynamic-scoping-fluid-pain.Yes, yes. I totally agree. This allows stack allocation of the variables as well, which can be a significant speed win (because of not making somuch garbage).
In some cases, but not all. Consider the Lisp version of an example I remember from my Scheme intro class:
(defun make-counter () (lexical-let ((count 0)) (lambda () (setq count (+ 1 count)) count)))In the Scheme version, and in Emacs with the cl package, a separate binding of "count" exists for each generated counter "object", so you can create and use several counters independently. If we want this to work in Guile-Elisp too, I don't think "count" can live on the stack in this case, since it has to survive past the return from make- counter. The dynamic-scoping-fluid-pain is replaced by lambda- environment-tracking-pain. :)
Without lambda or defun forms inside the lexical-let, yes, I think stack slots can be used. (Well, I'm kind of fuzzy on the whole call/ cc thing, but I assume that's already addressed elsewhere....)
Ken
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