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From: albert@spenarnc.xs4all.nl
Subject: Re: Juggling system-compilation items
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Date: Wed, 14 Aug 2024 12:58:16 +0200
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In article <v9gc9i$1nqu$1@dont-email.me>,
Gerry Jackson  <do-not-use@swldwa.uk> wrote:
>On 12/08/2024 10:45, albert@spenarnc.xs4all.nl wrote:
>> In article<v9bdpm$2sbsi$1@dont-email.me>,
>> Gerry Jackson<do-not-use@swldwa.uk>  wrote:
>>> ISTM that using the data stack to hold the control stack is an
>>> anachronism that was used in early Forth systems because of the limited
>>> amount of memory available. I also think that the system should not get
>>> in the way of user programs as putting control stack data on the data
>>> stack certainly does.
>> It alleviates restriction. Marcel Hendrix hated the restrictions of
>> R> >R and added the socalled "system stack" S> >S that can be used
>> over definitions. The disadvantage is of course that there are more
>> regions of memory that you have to keep track of.
>> I think that added complexity is a more important consideration as
>> memory usage. The more stacks you have and the more stack items
>> you keep in registers, the more difficult e.g. task switching becomes.
>
>As use of a control stack is during compilation, speed is not too
>important so why would register(s) be used for it?

The control stack pointer can be a user variable, so the switching
is automatic. 1) So you are right that it doesn't impose extra
restrictions for task switching.
Probably I was rationalizing that I hate making things more complicated.
Having a separate control flow stack is a complication in itself,
but it makes other things simpler.
I have the example of restricting STATE to [ ] and INTERPRET.
Marcel Hendrix has the example of passing data to a definition.
There are probably more.

1) By swapping the user pointer, all user variables are switched.

>
>--
>Gerry
>
Groetjes Albert
-- 
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