Re: What does "lacks a prefix" mean?

[Barry Margolin]

In article <mailman.6643.1436488423.904.help-gnu-emacs@gnu.org>,
 Drew Adams <drew.adams@oracle.com> wrote:

> > > And non-parallelizable theoretically :)
> > 
> > Regular let isn't parallelizable. It specifies that the value
> > expressions are evaluated in order.
> > 
> > The only difference between the two is the environment within which
> > later expressions are evaluated.
> 
> FWIW, Common Lisp specifies that "let performs the bindings
> in parallel and let* does them sequentially."

It specifies that the bindings are done in parallel, but evaluation of 
the initialization forms is sequential. From

http://www.lispworks.com/documentation/HyperSpec/Body/s_let_l.htm#let

"LET ... first evaluates the expressions init-form-1, init-form-2, and 
so on, in that order, saving the resulting values. Then all of the 
variables varj are bound to the corresponding values"

whereas 

"LET* ... first evaluates the expression init-form-1, then binds the 
variable var1 to that value; then it evaluates init-form-2 and binds 
var2, and so on"

If the forms have no side effects, LET can indeed execute them in 
parallel, since there's no way to tell the difference. LET* can also do 
that for any initialization expressions that don't refer back to earlier 
variables and have no side effects.

-- 
Barry Margolin, barmar@alum.mit.edu
Arlington, MA
*** PLEASE post questions in newsgroups, not directly to me ***