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From: minforth@gmx.net (minforth)
Newsgroups: comp.lang.forth
Subject: Re: Back & Forth - Co-routines
Date: Sun, 9 Feb 2025 19:15:29 +0000
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On Sun, 9 Feb 2025 17:55:29 +0000, Paul Rubin wrote:

> anton@mips.complang.tuwien.ac.at (Anton Ertl) writes:
>> The :}D means that the closure data is stored in the dictionary; there
>> is also :}L (for locals, deallocated when the surrounding definition
>> is exited), :}H (heap, deallocated with FREE-CLOSURE), and :}H1 (heap,
>> deallocated right after the first (and only) execution).
>
> This is pretty cool, but it looks like quotations within the closure
> aren't allowed to access the closure's locals, using them as OOP-like
> state.  In the current Gforth git snapshot:
>
>     : x [{: n :}d [: n 1+ dup to n ;] ;]h 0 execute ;
>
> gives:
>
>     *the terminal*:26:30: error: Unsupported operation
>     : x [{: n :}d [: n 1+ dup to >>>n<<< ;] ;]h 0 execute ;
>
> This is an attempt to make a counting function, like in Scheme:
>
> (define (x)
>   ((lambda (n)
>     (lambda ()
>       (set! n (+ 1 n))
>       n)) 0))
>
> (define a (x))
>
> (a)  ; 1
> (a)  ; 2, etc.

FWIW a single quotation-based counter in another Forth:

MinForth 3.6 (32 bit)
# defer ctr  ok
# : init { n } [: n 1+ dup to n ;] ;  ok
# 4 init is ctr  ok
# ctr . 5  ok
# ctr . 6  ok
# ctr . 7  ok
#

Generalisation would of course require closures and memory
management after use.

IOW read/write access to locals of the parent function opens
up new possiblities in Forth - perhaps also an idea for gforth.