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Re: Always using let*


From: Pascal J. Bourguignon
Subject: Re: Always using let*
Date: Tue, 16 Sep 2014 02:38:21 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3 (gnu/linux)

Emanuel Berg <address@hidden> writes:

> Stefan Monnier <address@hidden> writes:
>
>> which is usually understood as "use parallel
>> processing", aka "make use of multiple computational
>> units at the same time".
>
> Yes - this is my definition of parallelism as well:
> true concurrency, not perceived (as in preemption,
> context switching, and so on).
>
> The question is: does any Lisp do this with `let'?
>
> If yes, that Lisp could do it partly with let* as well
> only that would imply an overhead to sort out where
> there are precedence constraints.
>
> The appeal of doing it for let is that it wouldn't be
> any fuss - just distribute, compute, and execute the
> body all set. But if no one did it, some practical
> obstacle must still have gotten into the way...

Well, the actual reason why LET and LET* are the way they are, is purely
history.

Somebody invented LET first.  Then somebody noted that they had
sometimes to write (let ((a 1))
                     (let ((b (+ a 1)))
                       (let ((c (+ a b)))
                          …)))
so they wrote the LET* macro to do that, and it stayed that way since
then.

Perhaps one LISP had it reversed, but since it was in the minority, when
they documented the common lisp language, it was LET/LET* we know that
won.  Notice that emacs lisp is in the majority here.

-- 
__Pascal Bourguignon__                 http://www.informatimago.com/
“The factory of the future will have only two employees, a man and a
dog. The man will be there to feed the dog. The dog will be there to
keep the man from touching the equipment.” -- Carl Bass CEO Autodesk


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