On Jul 23, 2009, at 16:46, Andy Wingo wrote:
On Tue 21 Jul 2009 15:10, Daniel Kraft <d...@domob.eu> writes:
Just a little addition to the subject of extensions: I'd very much
like
to 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
so
much 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
