Re: 0 SET-ORDER why?

In article <v5m2po$3811n$2@dont-email.me>,
Ruvim  <ruvim.pinka@gmail.com> wrote:

On 2024-06-27 08:14, Gerry Jackson wrote:

On 26/06/2024 14:36, Ruvim wrote:

One possible use case:
>
   : turnkey ( -- ) 0 set-order
     also Target definitions
     also Minimal also
   ;

>
ALSO duplicates the wordlist at the head of the search order. If the
search order is empty there is nothing to duplicate. Therefore ALSO
applied to an empty search order ought to be an ambiguous condition.

>
Agree. This code is formally incorrect.
>
An ambiguous condition should be declared for ALSO
when the search order is empty.
>
I collect such cases at
<https://github.com/ForthHub/standard-evolution/issues/5>
>
Then a proposal should be prepared.
>
>

>
Presumably the above definition works because a target wordlist replaces
whatever garbage ALSO leaves in the search order. So the definition
might as well have 0 1 SET-ORDER instead of 0 SET-ORDER ALSO.
Or better still TARGET-WORDLIST 1 SET-ORDER. Either removes the above
justification for 0 SET-ORDER.

>
As I later discovered, this "turnkey" is from Gforth, and it was corrected:
<https://github.com/forthy42/gforth/blob/ba915873/cross.fs#L4570>
>
>

But having said that it is better for 0 SET-ORDER to do what is natural
instead of yet another ambiguous condition.
>
 > Another possible use case:
 >
 >    : s-to-n ( addr u -- n )
 >      depth >r
 >      get-order n>r 0 set-order
 >        ['] evaluate ['] execute-interpreting catch
 >      nr> set-order
 >      depth 1- r> <> if -12 throw then
 >    ;

>
There is a mistake (due to additions in my old example)
>
A corrected variant:
>
  : s-to-n ( addr u -- x )
    depth >r
    get-order n>r 0 set-order
      ['] evaluate ['] execute-interpreting catch
    nr> set-order  throw
    depth 1+ r> <> if -12 throw then
  ;
>
>

>
This is a better use case e.g. if BASE is greater than decimal 10
converting an alphanumeric string to a number could clash with a word in
the dictionary. Having an empty search order eliminates that possibility.
>
Incidentally another possibility is that if ['] EVALUATE is replaced in
the above definition with ['] SOME-RECOGNISER, that could be the basis
for an ANS/FORTH 2012 compatible way of implementing recognisers. If the
recogniser fails restore the search order and try again.

>
>
My position is that no recognizer can have side effects (other then
items on the data stack and/or floating-point stack).

I second that. Moreover the items would have to be the same in
interpret and compilation mode.
At least as a starting point, otherwise Forth degenerates to a
tangled web of special purpose interpreters.

>
Although, this approach can be used to *implement* SOME-RECOGNISER.
>
>
--
Ruvim

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