Re: Always using let*

[Barry Margolin <barmar@alum.mit.edu>]

In article <87mwa1lhb1.fsf@kuiper.lan.informatimago.com>,
 "Pascal J. Bourguignon" <pjb@informatimago.com> wrote:

> Stefan Monnier <monnier@iro.umontreal.ca> writes:
> 
> >> Lisps such as Common Lisp were specifically designed with this
> >> parallel evaluation in mind.  The spec (and CLTL(2)) specifically
> >> emphasizes the inherent parallelism (independence) here that
> >> implies the *possibility* of parallel evaluation.
> >
> > I simply claim that this is bogus.  Only the var-binding is "parallel", not
> > the computation of each value.  So it's a "parallel binding" semantics,
> > but it has nothing to do with efficient execution on multiple
> > execution units.
> 
> The claim is not bogus.  It's just that in general, in presence of side
> effects, since the expressions must be evaluated from left to right,
> indeed, only the assignments can be performed in parallel.

If the LET can be done in parallel, so could LET*. Remember, we're 
talking about compiled code. The inner and outer variables are not the 
same memory location, even if they have the same name. The difference 
between LET and LET* just has to do with which scope the compiler looks 
up the name in.

-- 
Barry Margolin, barmar@alum.mit.edu
Arlington, MA
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