Re: Back & Forth - Co-routines

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.