Run Plugin:"c:\users\craig\mail\attach\Re Macros Scheme vs Common Li3.ems

Content-Type: text/plain; charset=US-ASCII Date: Thu, 27 Aug 1998 19:43:24 -0400 From: Craig Lanning <CraigL(a)internetx.net&gt; At 07:13 AM 8/27/98 -0400, Rick Campbell wrote: > > From: sperber(a)informatik.uni-tuebingen.de (Michael Sperber [Mr.

> Date: 26 Aug 1998 14:20:32 +0200 > > I suspect your CL actually processes the forms in some weird > order. In any case, I strongly doubt that the CL standard > mandates the behavior you describe. > >Common Lisp does not mandate much of anything regarding when expansion >occurs. It's an implementation detail, i. e. you should not write >code that depends on expansion happening at a certain time. That's not really true. All forms are processed in order from left to right. Macros are expanded as they are reached. In compiled code, macros are expanded at compile time in such a way as not be expanded at runtime. I'm pretty sure that you're wrong about this. At the risk of being hypocritical (I didn't cite spec), can you point to something in the spec that dictates that in compiled code, macros *must* be expanded at compile time. I believe an implementation is allowed to expand macros at read time and then compile whatever's been previously expanded at compile time, e. g.

* (defmacro foo ...) * (defun bar () ... (foo ...)) ; expand macro here * (defmacro foo ...) ; inconsistent with first definition * (compile 'bar) ; uses first definition of foo cuz it was already expanded At least, I've never seen spec saying the above is taboo and I believe that I've seen discussion saying that it's allowed.