Re: "Back & Forth" - Local variables

In article <nnd$44fc771d$089c856c@db10b46852f85b89>,
Hans Bezemer  <the.beez.speaks@gmail.com> wrote:

On 09-01-2025 13:42, dxf wrote:

There is no guarantee that a saved interpreter pointer on the
stack is an execution token.

>
Nope - in ANS-Forth it is listed as:
>
nest-sys; definition calls; implementation dependent
>
So - that's obvious. But in 4tH it works out. And defining it as >R
works out as well. BTW, I've tested the thing - and it holds up.
>
I got my work cut out for a next episode! On co-routines! ;-)
>
Hans Bezemer
>
BTW, I've heard there are implementations where nest-sys aren't even on
the return stack. The standard seems to confirm this:
>
return stack:  A stack that _MAY_BE_ used for program execution nesting,
do-loop execution, temporary storage, and other purposes.
>
.. and sorry to spoil the fun, but what we're doing here is illegal anyways:
>
"A program shall _NOT_ access values on the return stack (using R@, R>,
2R@ or 2R>) that it _DID_NOT_ place there using >R or 2>R;"
>
In other words: your mileage may (be) very, very illegal.

The use of CO / ;: can't be illegal. Its implementation may not be
portable, that is another matter.
There is no reference  to the return stack in the glossary of CO.

========================
 CO

STACKEFFECT:

DESCRIPTION: []

Return to the caller, suspending interpretation of the current
definition, such that when the caller exits, this definition is
resumed. The return stack must not be engaged, such as between >R and
R> , or DO and LOOP .

GLOSSARY INDEX

SEE ALSO: CONTROL   EXIT
========================
Merely a warning that the ciforth implementation doesn't work well with
certainly manipulations of the return stack.

The strict forbidden of nested definitions is non-sensical,
I allow nested definitions in ciforth with an extension.
: aap { : add + ; ]  1 2 add 3 4 add * ;
The program is non-standard, but if this extension is loaded the Forth
is still conforming.

>
Hans Bezemer
>

Groetjes Albert
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