Re: Back & Forth - Co-routines

On 2025-02-02 15:13, albert@spenarnc.xs4all.nl wrote:

In article <vnkvvq$2a5o$1@dont-email.me>, Ruvim  <ruvim.pinka@gmail.com> wrote:

On 2025-01-31 11:33, dxf wrote:

>
Not sure if previously mentioned but here's another version of LOCAL
>
: ;:  >r ;
>
: LOCAL ( x adr -- )
    r> -rot dup @ over 2>r ! ;: 2r> ! ;
>
variable A  variable B  8 a !  7 b !
>
: divide ( a b -- )  b local  a local
    a @  b @  /  . cr  ;
>
15 3 divide  a ? b ?
>

>
>
This approach does not work well with catch/throw. Because `throw` must
restore the values of all "local" variables that are used in the
definitions whose execution is being terminated. And this is difficult
to implement.
>
>
See also 13.3.3.1, item c,
<https://forth-standard.org/standard/locals#subsubsection.13.3.3.1>
>
| ABORT shall release all local storage resources,
| and CATCH / THROW (if implemented) shall release
| such resources for all definitions whose execution
| is being terminated.

 Nice catch!
 However, this is highly artificial. You have to have a recursive routine in this
vein:
 RECURSIVE
: fun .. fun ... fun . 'fun CATCH .. fun  ... ;
 otherwise the global VARIABLE's can be ignored.
 I would be interested to see a remotely plausible example of this.
Mixing recursion and exception is ill advised by iq<160.

Recursion is not necessary. It is enough to use the same-name "local" variables in different functions, some of which throw exceptions, and other catch exceptions.
An artificial example:
: local ( x2 addr1 -- ; R: nest-sys1 -- x1 addr1 nest-sys.xt nest-sys1 )
   \ This definition assumes that nest-sys size is 1 cell,
   \ and xt is a subtype of nest-sys
   r>  ( x2 addr nest-sys1 )
   over dup @ >r >r  [: 2r> ! ;] >r
   ( x2 addr1  nest-sys1 ) >r  !
;
: idiv ( n1 n2\0 -- n3  |  n1 0 -- never )
   dup if / exit then -10 throw
;
variable a
variable b
: foo ( n1 n2 -- )
   b local  a local
   a @  b @  idiv
   ."  idiv result is " . cr
;
: bar ( u1 -- u1 )
   a local
   100  a @  ['] foo catch if 2drop then
   a @
;
0 bar .
\ this must print 0, but will print 10
--
Ruvim