[r6rs-discuss] [Formal] Disallow redefinitions macros/variables

From: Abdulaziz Ghuloum <aghuloum>
Date: Tue Mar 27 22:50:09 2007

On Mar 27, 2007, at 8:24 PM, William D Clinger wrote:

> Andre van Tonder correctly observed that the change
> to letrec* semantics for internal definitions will
> make optimization more difficult. With the letrec*
> semantics, Scheme programmers would just have to
> learn that internal definitions are assignments in
> disguise,

Weren't the semantics of internal definitions equivalent
to the semantics of letrec in R5RS? If so, then Scheme
programmers should've already learned that internal
definitions are assignments in disguise, no?

I think Andre's comment would've been applicable even
if the semantics of internal defines were to remain
equivalent to letrec. So, whether internal defines are
letrec or letrec* is orthogonal to the issue at hand.

While I personally prefer letrec over letrec* semantics
for internal definitions, for the majority of the code
that I write, I see no big difference in the efficiency
of the code I generate. The reason may well be that for
the code that I write, I try to follow the rules you
listed (whenever possible) unless I know the compiler
handles some additional cases like (if 1 2 3) :-)

Yes, performance may degrade at times when a compiler is
presented with code outside of its capacity to optimize.
This is true of any compiler. To maximize performance,
you bring the code and compiler closer by making the code
simpler or by making the compiler more sophisticated.
Do you see another way around it?

Aziz,,,
Received on Tue Mar 27 2007 - 22:49:32 UTC