Re: "Back & Forth" - Local variables

On 9/01/2025 6:13 am, albert@spenarnc.xs4all.nl wrote:

In article <nnd$032b844d$734ee136@776df242e330d1d2>,
Hans Bezemer  <the.beez.speaks@gmail.com> wrote:

On 08-01-2025 17:27, albert@spenarnc.xs4all.nl wrote:
>

I was impressed with the Behringer solution.
(I didn't care about the politically correct solution.)
>
====================================
: local{ R> SWAP DUP >R @ >R >R ;
: }global R> R> R> ! >R ;
=================
>
But I can do you one better.
Remember the word ;: from colorforth. That is actually a coroutine call.
I call it CO. (Present in ciforth since the year 00)

>
<snipped>
>

>
With CO the example become
---------------------------------------
: LOCAL   R> SWAP DUP >R @ >R >R   CO   R> R> ! ;
>
VARIABLE A
VARIABLE B
>
: divide
    A LOCAL
    B LOCAL
    B ! A !  A @ B @ /
    . CR
;
>
15 3 divide
---------------------------------------
>
This saves a definition and a word-of-code, and a line for every
LOCAL used. Now that is closer to what Chuck Moore would have used.
Remember for Moore CO aka ;: is a standard word.
>
CO is not standard but it should be, and it is elementary as hell.

>
Couldn't find the source for either CO or ;: but I got some primitive,
high level form of co-routine in 4tH:
>
====================================
: yield r> r> swap >r >r ;             \ remember that ; compiles EXIT!
aka rdrop grab                         \ so add a [FORCE] when needed.
====================================

 
That is the equivalent in high level code.
 
In assembler, assuming ESI is the interpreter pointer and EBP is the return
stack pointer:
 
CODE CO
            XCHG    ESI,[EBP]
            NEXT,
END-CODE
 
In assembler the return stack is uncluttered.
...

Just to clarify CO (coroutines) and

: ;:  >r ;

are different albeit related beasts.  So which one is Moore's?

BTW the latter is equivalent to the 'docol' run-time in most DTC forth.
In my case I'd just need to give the code fragment a name.  But is this
latter ;: worth it?  Its use seems to be restricted to restoring state
when a word completes.  It's not a "coroutine.

>
Can't say how they measure up. But I guess co-routines is something
Chuck would like - since it's something you can implement quite easily.
So yes, I agree Chuck wouldn't waste that line ;-)
>
Hans Bezemer