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From: Jeff Barnett <jbb@notatt.com>
Newsgroups: comp.lang.lisp
Subject: Re: History of lexical scope in Lisp
Date: Sun, 17 Mar 2024 16:42:34 -0600
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On 3/16/2024 11:37 PM, Lawrence D'Oliveiro wrote:
> On Sat, 16 Mar 2024 23:13:20 -0600, Jeff Barnett wrote:
> 
>> However if your point is that you can build "simulations" of one sort of
>> scoping out of primitives for another sort ...
> 
> No, my point was that there seems to be no need for dynamic scoping, if
> the only excuse anyone can come up for needing it comes out of exception
> handling.

That wasn't the only thing mentioned. In fact it was said to be quite 
useful and desired without enumeration of reasons. You of course chopped 
  many original messages above to remove some of those "short glowing 
reviews" then got on your hobby horse and started to ride.

Just think of the following when specifying a variable's intent: is it 
supposed to influence an evaluation or is it supposed to influence an 
evaluation when it's in a particular lexical scope? Does that help you any?

The example of error handling is that it's generally supposed to control 
an evaluation. If error handling was lexically based then you would need 
to decide what to do when evaluate(x) occurs and the handling of certain 
conditions are specified in a scope not available when x was defined. 
There are choices and lots of them. When dynamic and lexical flow trees 
are different, you must decide by language rules or provide primitives 
to users that allows them to sort out intent. If you don't have any 
"special" variables around, you'll find that rather difficult.

Lexical-only is nice and neat for many applications and philosophies of 
programming. But not all by a long shot. If that approach satisfies you, 
I'd suggest ALGOL or even SIMULA. Alan Perlis even saw uses for dynamic 
visibility (private communications) and discussed the thought that OWN 
variables did not satisfy those uses. There was an ambiguity in the 
second ALGOL spec on the requirements for OWN variables: if the spec was 
read one way, a particular function computed a Legendre polynomial; read 
the other way, it computed a Bessel function! (It's been a long time and 
I don't remember the exact pair of function families that were 
confounded.) In any event, the issue had to do for the rules about when 
an OWN needed to be bound and it was possible to have multiple bindings 
simultaneously! I believe this latter fact was tied up with trying to 
allow OWNS to act more like SPECIAL.
-- 
Jeff Barnett