Subject: Re: Lisp is *SLOW* From: Erik Naggum <firstname.lastname@example.org> Date: 1997/08/08 Newsgroups: comp.lang.lisp Message-ID: <email@example.com> * Jamie Zawinski | If you have a recursive function that does a dynamic bind, or allocation, | or whatever, around each call to itself, then I wouldn't consider that | tail-recursive. Sure, you've saved the call-stack, but that's not the | whole story. I agree that it's not the whole story, but I'm talking more about the general ability to do tail-call merging than when specifically applied to calling yourself. my point was that other call-related expenses may be worth saving. e.g., on a SPARC, stack growth per call is large, and the cost of save and restore involving register windows moved to and from stack is very high. other CPUs have other costs. we do tail-call merging for several good reasons and I believe all of them are related to reducing costs, so if we can identify additional costs and ways to reduce them, that would be a win. | What reasons were you thinking of? Perhaps there are also *other* | reasons not to attempt to do tail-calls with emacs-lisp, but the dynamic | binding showstopper was the point at which I stopped thinking about it... I wanted to show that the way dynamic bindings and unwind-protects are organized into a separate stack in Emacs Lisp (and probably not _entirely_ differently in other Lisps) was not an argument _against_ tail-call merging in the presence of these forms. you argue against tail-call merging based on other factors in Emacs Lisp, and that's cool -- I didn't expect Emacs Lisp to get tail-call merging just because it's possible, when it isn't cost effective. the question is only "how do you know how far to unwind", and if that is something like a "mark" on a stack, like in Emacs Lisp, instead of constant number of elements on the stack, like the C calling convention where the caller must clean up the stack, I see opportunities for saving more costs. not that I know any other Lisp intimately, but from what I have read elsewhere, this does seem like a straight-forward way to do it, and would, in other words, not remove the prospect of having efficient function calls through the use of tail-call merging just because more powerful features are also needed and used. | Emacs-lisp isn't a good example of much of anything, really. maybe not a _good_ example of anything, but a valid example of many things. I'm aware that you don't like Emacs Lisp, and I have my own set of gripes, but that doesn't mean everything that comes from Emacs Lisp is tainted. #\Erik -- 404 Give me a URL I cannot refuse.