Re: Back & Forth - Co-routines

In article <2025Feb10.081905@mips.complang.tuwien.ac.at>,
Anton Ertl <anton@mips.complang.tuwien.ac.at> wrote:

melahi_ahmed@yahoo.fr (ahmed) writes:

On Sun, 9 Feb 2025 23:08:22 +0000, Anton Ertl wrote:
>

Paul Rubin <no.email@nospam.invalid> writes:

..

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))

...

: x ( -- xt )
  here 0 , [{: addr :}d addr @ 1+ dup addr ! ;] ;
>
x alias a

...

: ctr: create 0 , does> dup @ 1+ dup rot ! ;  ok
ctr: a

...

So, what is the difference between the two definitions?

>
One produces an xt, the other a named word; the latter is more
convenient for the shown usage).
>
But yes, for dictionary allocation Forth has had a way to associate
data with a single action since very early on.

Make that
"
    Forth has had a way to associate
    data with a single action since very early on.
"
or more precise
" Forth recipes combine code and data"

Using underlying more primitive facilities in a Forth, one can define
a recipe ("xt") that has no name, is not linked in a wordlist and sits
in ALLOCATEd space and perform an action like x.
(Admittedly, in a Forth that separates code and data it is more involved)

This is a simple example to get a word `test floating in allocated space.
(In ciforth example)

ALLOC moves a word to the heap freeing the a freshly generated object

that runs from ( addr --) to HERE. This doesn't switch DP, and assumes
relocatable code.
UNLINK-LATEST decouples the latest word from the dictionary.

WANT >ALLOC UNLINK-LATEST
INIT-ALLOC   \ Use 1/4 of the dictionary space for heap.

: test "hello" TYPE ;
' test UNLINK-LATEST  \ decouple

ALLOC  \ move to heap

WORDS \ to show that test has vanished
.S    \ The xt
EXECUTE
hello OK

In the above example reclaiming memory is not harder than with
any dynamically allocated memory.

[This doesn't show how the data is coupled, but conveys hopefully
a part of the idea.]

<SNIP>

But, as mentioned below, the textbook examples of changing data in
closures or DOES> words are rarely found in practice.

I totally agree on this. In 400+ euler problems I was never inclined
to use this technique (if this counts for something ..)

<SNIP>

- anton

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