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Re: non-parsing `TO` considered harmful

From Ruvim <ruvim.pinka@gmail.com>
Newsgroups comp.lang.forth
Subject Re: non-parsing `TO` considered harmful
Date 2026-06-06 12:54 +0000
Organization A noiseless patient Spider
Message-ID <110159o$1rm6n$1@dont-email.me> (permalink)
References (1 earlier) <10r1825$2d8j6$1@dont-email.me> <nnd$7d2e6a4e$3bd4aa4f@294189cda32d8f1f> <10r3nfo$33464$1@dont-email.me> <nnd$1df5c626$6d97c61c@066801e65fcbf8a0> <10vsu39$neci$1@dont-email.me>

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On 2026-06-04 22:26, Ruvim wrote:
> On 2026-04-08 10:34, albert@spenarnc.xs4all.nl wrote:
>> In article <10r3nfo$33464$1@dont-email.me>,
>> Gerry Jackson  <do-not-use@swldwa.uk> wrote:
>>> On 07/04/2026 12:35, albert@spenarnc.xs4all.nl wrote:
>>>> A similar situation applies to "TO must scan". It turns out there
>>>> is no standard program that can detect this. It steers implementation
>>>> towards a scanning TO.
>>>
>>> On the contrary, Ruvim posted some code that is a standard program and
>>> which distinguises between a parsing TO and one that sets a flag for a
>>> following VALUE to act on.
>>>
>>> I can't find the post but the gist of it was (I think):
>>>
>>> 1 value v1
>>> 2 value v2 immediate
>>> : test  to v2 v1  ;
> 
> Yes, something similar.
> 
>>> Running test with
>>> 3 test
>>> A parsing TO will set v2 to 3
> 
> Yes, and this is specified by the standard.
> 
>>> A flagging TO will execute v2 during compilation of test because it is
>>> immediate. So test will set v1 to 3 leaving v2 unchanged.
>>
>> No it doesn't. It leaves garbage on the stack during compilation,
>> leading to mostly an error.
>> I leave it up to the reader whether this counts as a standard program.
> 
> The provided program conforms to the Forth-94 standard and later versions.
> 
> A system that fails that test does not conform to the standard with 
> respect to `to`.
> 
> 
> Historically, there were two approaches to implement `to`: "parsing" and 
> "non-parsing" [1]. Forth-94 formally specified the "parsing" approach:
> 
>      | ANS Forth explicitly requires that TO must parse,
>      | so that TO's effect will be predictable when
>      | it is used at the end of the parse area.
> 
> 
> OTOH, it disallowed applying the words `postpone` and `[compile]` to 
> `to` [2]. Perhaps, this was done as a concession to implementations that 
> adhered to the "non-parsing" approach, to prevent behavior variations in 
> a standard program caused by deviations in implementations of `to`.
> 
> [1] <https://forthhub.github.io/forth-sf-net/standard/dpans/ 
> dpansa6.htm#A.6.2.2295>
> [2] https://forthhub.github.io/forth-sf-net/standard/dpans/ 
> dpans6.htm#6.2.2295
> 
> 
> Here is an example of a program that relies on a parsing `to`, but is 
> not compliant due to that very ambiguous condition regarding `postpone`.
> Let's introduce a multiple assignment construct of the following form:
> `1 2 3  to( a b c )`.
> 
> 
>    : ?comp ( -- ) state @ if exit then -14 throw ;
> 
>    : equals ( sd2 sd1 -- flag )
>      dup 3 pick <> if 2drop 2drop false exit then
>      compare 0=
>    ;
>    : source-offset ( -- u )
>      >in @
>    ;
>    : set-source-offset ( u -- )
>      source nip over u< invert if >in ! exit then
>      -18 throw \ "parsed string overflow"
>    ;
> 
>    synonym take-lexeme-maybe parse-name
> 
>    : take-lexeme ( "ccc" -- sd )
>      take-lexeme-maybe dup if exit then -16 throw
>    ;
> 
>    : to( ( "ccc<rparen>" -- ) \ " a b c )"
>      ?comp  source-offset ( u.offset )
>      take-lexeme s" )" equals if drop exit then
>      ( u.offset ) recurse ( u.offset )
>      source-offset  swap set-source-offset
>        postpone to
>      set-source-offset
>    ; immediate
> 
>    \ usage example
> 
>    0 value a
>    0 value b
> 
>    : init-foo ( -- ) 2 3  to( a b ) ;
> 
>    init-foo  a . b .  \ it should print "2 3"



Do you know a Forth system in which `to` parses the parse area and in 
which the definition for `to(` given above *does not* work?


How do you implement a construct `to( ... )` that works both in 
interpretation state and in compilation state?

Obviously, we should remove `?comp` and store the offsets on the return 
stack.

Also, we could replace `postpone to` with
   `state @ if  postpone to  else  ['] to execute  then`

In classic single-xt systems, things are simpler: it suffices to replace 
it with `['] to execute`.


Interestingly, the Recognizer API does not help in implementing this 
construct.



--
Ruvim

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Coroutines in Forth Gerry Jackson <do-not-use@swldwa.uk> - 2026-04-05 23:25 +0100
  Re: Coroutines in Forth Gerry Jackson <do-not-use@swldwa.uk> - 2026-04-05 23:30 +0100
    Re: Coroutines in Forth Paul Rubin <no.email@nospam.invalid> - 2026-04-05 17:16 -0700
      Re: Coroutines in Forth Gerry Jackson <do-not-use@swldwa.uk> - 2026-04-06 19:58 +0100
        Re: Coroutines in Forth Paul Rubin <no.email@nospam.invalid> - 2026-04-22 11:13 -0700
          Re: Coroutines in Forth albert@spenarnc.xs4all.nl - 2026-04-22 22:05 +0200
      Re: Coroutines in Forth albert@spenarnc.xs4all.nl - 2026-04-07 13:23 +0200
  Re: Coroutines in Forth albert@spenarnc.xs4all.nl - 2026-04-06 13:51 +0200
    Re: Coroutines in Forth Gerry Jackson <do-not-use@swldwa.uk> - 2026-04-06 22:20 +0100
      Re: Coroutines in Forth albert@spenarnc.xs4all.nl - 2026-04-07 13:35 +0200
        Re: Coroutines in Forth Gerry Jackson <do-not-use@swldwa.uk> - 2026-04-07 20:55 +0100
          Re: Coroutines in Forth albert@spenarnc.xs4all.nl - 2026-04-08 12:34 +0200
            Re: Coroutines in Forth Gerry Jackson <do-not-use@swldwa.uk> - 2026-04-08 12:32 +0100
            non-parsing `TO` considered harmful Ruvim <ruvim.pinka@gmail.com> - 2026-06-04 22:26 +0000
              Re: non-parsing `TO` considered harmful Ruvim <ruvim.pinka@gmail.com> - 2026-06-06 12:54 +0000
                Re: non-parsing `TO` considered harmful anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2026-06-06 16:17 +0000
                Re: non-parsing `TO` considered harmful Ruvim <ruvim.pinka@gmail.com> - 2026-06-06 21:09 +0000
                Re: non-parsing `TO` considered harmful anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2026-06-07 13:23 +0000
                Re: non-parsing `TO` considered harmful Ruvim <ruvim.pinka@gmail.com> - 2026-06-07 17:44 +0000
                Re: non-parsing `TO` considered harmful anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2026-06-08 05:04 +0000
                text translator (was: non-parsing `TO` considered harmful) Ruvim <ruvim.pinka@gmail.com> - 2026-06-08 15:53 +0000
                Recognizers vs Parsing words (was: non-parsing `TO` considered harmful) Ruvim <ruvim.pinka@gmail.com> - 2026-06-09 10:25 +0000
                Re: Recognizers vs Parsing words Ruvim <ruvim.pinka@gmail.com> - 2026-06-10 19:45 +0000
                compilation of compilation (was: non-parsing `TO` considered harmful) Ruvim <ruvim.pinka@gmail.com> - 2026-06-08 07:28 +0000
                Recognizer API v.2025-09-11 (was: non-parsing `TO` considered harmful) Ruvim <ruvim.pinka@gmail.com> - 2026-06-14 12:41 +0000
                Re: Recognizer API v.2025-09-11 (was: non-parsing `TO` considered harmful) anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2026-06-15 17:17 +0000
                Re: Recognizer API v.2025-09-11 Ruvim <ruvim.pinka@gmail.com> - 2026-06-16 17:34 +0000
                Re: Recognizer API v.2025-09-11 anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2026-06-17 05:05 +0000
                Setters and getters in APIs (was: Recognizer API v.2025-09-11) Ruvim <ruvim.pinka@gmail.com> - 2026-06-19 16:17 +0000
                Re: Setters and getters in APIs (was: Recognizer API v.2025-09-11) anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2026-06-20 15:51 +0000
                Re: non-parsing `TO` considered harmful Stephen Pelc <stephen@vfxforth.com> - 2026-06-07 11:59 +0000
                Re: non-parsing `TO` considered harmful anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2026-06-07 15:25 +0000
          Re: Coroutines in Forth Stephen Pelc <stephen@vfxforth.com> - 2026-04-09 10:12 +0000
            non-parsing `TO` considered harmful Ruvim <ruvim.pinka@gmail.com> - 2026-06-04 22:30 +0000
              VFX Forth problems Ruvim <ruvim.pinka@gmail.com> - 2026-06-05 16:24 +0000
            Re: Coroutines in Forth marcel hendrix <mhx@iae.nl> - 2026-07-09 09:50 +0200
              Re: Coroutines in Forth albert@SPENARNC.XS4ALL.NL - 2026-07-10 01:48 +0200
          Re: Coroutines in Forth Stephen Pelc <stephen@vfxforth.com> - 2026-06-07 11:53 +0000
            non-parsing `TO` considered harmful (was: Coroutines in Forth) Ruvim <ruvim.pinka@gmail.com> - 2026-06-07 13:31 +0000
              Re: non-parsing `TO` considered harmful Travis Bemann <tabemann@gmail.com> - 2026-08-28 20:36 -0500
        Re: Coroutines in Forth Hans Bezemer <the.beez.speaks@gmail.com> - 2026-04-10 19:01 +0200
          Re: Coroutines in Forth dxf <dxforth@gmail.com> - 2026-04-11 11:54 +1000
            Re: Coroutines in Forth Hans Bezemer <the.beez.speaks@gmail.com> - 2026-05-01 13:07 +0200
          Re: Coroutines in Forth peter <peter.noreply@tin.it> - 2026-04-11 09:49 +0200
          Re: Coroutines in Forth albert@spenarnc.xs4all.nl - 2026-04-11 22:03 +0200
            Re: Coroutines in Forth dxf <dxforth@gmail.com> - 2026-04-12 12:49 +1000
              Re: Coroutines in Forth albert@spenarnc.xs4all.nl - 2026-04-12 12:13 +0200
                Re: Coroutines in Forth Hans Bezemer <the.beez.speaks@gmail.com> - 2026-04-12 17:39 +0200
                Re: Coroutines in Forth dxf <dxforth@gmail.com> - 2026-04-13 10:54 +1000
                Re: Coroutines in Forth Hans Bezemer <the.beez.speaks@gmail.com> - 2026-04-13 19:24 +0200
              Re: Coroutines in Forth Hans Bezemer <the.beez.speaks@gmail.com> - 2026-04-12 13:48 +0200
              Re: Coroutines in Forth albert@spenarnc.xs4all.nl - 2026-04-13 12:13 +0200
              Re: Coroutines in Forth Paul Rubin <no.email@nospam.invalid> - 2026-04-22 11:18 -0700
                Re: Coroutines in Forth dxf <dxforth@gmail.com> - 2026-04-23 11:13 +1000
                Re: Coroutines in Forth Hans Bezemer <the.beez.speaks@gmail.com> - 2026-04-23 12:37 +0200
                Re: Coroutines in Forth Paul Rubin <no.email@nospam.invalid> - 2026-04-24 10:36 -0700
                Re: Coroutines in Forth dxf <dxforth@gmail.com> - 2026-04-25 12:12 +1000
                Re: Coroutines in Forth Paul Rubin <no.email@nospam.invalid> - 2026-04-24 23:31 -0700
                Re: Coroutines in Forth albert@spenarnc.xs4all.nl - 2026-04-25 10:45 +0200
                Re: Coroutines in Forth dxf <dxforth@gmail.com> - 2026-04-25 22:06 +1000
                Re: Coroutines in Forth Hans Bezemer <the.beez.speaks@gmail.com> - 2026-04-25 15:11 +0200
                Re: Coroutines in Forth dxf <dxforth@gmail.com> - 2026-04-26 13:33 +1000
                Re: Coroutines in Forth Hans Bezemer <the.beez.speaks@gmail.com> - 2026-04-26 16:28 +0200
                Re: Coroutines in Forth Paul Rubin <no.email@nospam.invalid> - 2026-04-25 21:46 -0700
                FP stack depth limitations (was: Coroutines in Forth) anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2026-04-26 05:55 +0000
                Re: FP stack depth limitations Paul Rubin <no.email@nospam.invalid> - 2026-04-26 00:28 -0700
                Re: FP stack depth limitations dxf <dxforth@gmail.com> - 2026-04-26 19:55 +1000
                Re: FP stack depth limitations (was: Coroutines in Forth) peter <peter.noreply@tin.it> - 2026-04-26 09:57 +0200
                Re: FP stack depth limitations (was: Coroutines in Forth) albert@spenarnc.xs4all.nl - 2026-04-26 14:34 +0200
                Re: Coroutines in Forth Hans Bezemer <the.beez.speaks@gmail.com> - 2026-04-25 15:01 +0200
                Re: Coroutines in Forth Hans Bezemer <the.beez.speaks@gmail.com> - 2026-05-01 13:13 +0200
                Forth, C, hardware, and programming virtues (was: Coroutines in Forth) anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2026-04-25 05:26 +0000
                Re: Forth, C, hardware, and programming virtues Paul Rubin <no.email@nospam.invalid> - 2026-04-24 23:55 -0700
                Re: Forth, C, hardware, and programming virtues anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2026-04-25 08:21 +0000
                Re: Forth, C, hardware, and programming virtues albert@spenarnc.xs4all.nl - 2026-04-25 11:27 +0200
                Re: Forth, C, hardware, and programming virtues Hans Bezemer <the.beez.speaks@gmail.com> - 2026-04-25 15:43 +0200
                Re: Forth, C, hardware, and programming virtues anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2026-04-25 17:21 +0000
                Re: Forth, C, hardware, and programming virtues dxf <dxforth@gmail.com> - 2026-04-26 15:21 +1000
                Re: Forth, C, hardware, and programming virtues Hans Bezemer <the.beez.speaks@gmail.com> - 2026-04-26 15:08 +0200
                Re: Forth, C, hardware, and programming virtues albert@spenarnc.xs4all.nl - 2026-04-26 00:34 +0200
                Re: Forth, C, hardware, and programming virtues Hans Bezemer <the.beez.speaks@gmail.com> - 2026-04-26 15:10 +0200
                locals (was: Coroutines in Forth) anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2026-04-25 04:47 +0000
                Re: locals Paul Rubin <no.email@nospam.invalid> - 2026-04-24 23:21 -0700
                Re: locals anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2026-04-25 06:43 +0000
                Re: locals albert@spenarnc.xs4all.nl - 2026-04-25 11:43 +0200
                Re: locals anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2026-04-25 10:22 +0000
                Re: locals peter <peter.noreply@tin.it> - 2026-04-25 16:07 +0200
                Re: locals Hans Bezemer <the.beez.speaks@gmail.com> - 2026-04-25 17:38 +0200
                Re: locals albert@spenarnc.xs4all.nl - 2026-04-26 01:13 +0200
                Re: locals anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2026-04-26 14:03 +0000
                Re: locals peter <peter.noreply@tin.it> - 2026-04-27 09:31 +0200
                Re: locals anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2026-04-27 07:53 +0000
                Re: locals peter <peter.noreply@tin.it> - 2026-04-27 11:52 +0200
                Re: locals albert@spenarnc.xs4all.nl - 2026-04-26 00:51 +0200
                Re: locals Paul Rubin <no.email@nospam.invalid> - 2026-04-25 22:40 -0700
                Re: locals albert@spenarnc.xs4all.nl - 2026-04-26 14:55 +0200
                Re: locals anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2026-04-26 09:50 +0000
                Re: locals Hans Bezemer <the.beez.speaks@gmail.com> - 2026-04-26 16:22 +0200
                Re: locals anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2026-04-26 17:04 +0000
                Re: locals dxf <dxforth@gmail.com> - 2026-04-27 11:51 +1000
                Re: locals Hans Bezemer <the.beez.speaks@gmail.com> - 2026-04-28 08:21 +0200
                Re: locals Hans Bezemer <the.beez.speaks@gmail.com> - 2026-04-28 08:22 +0200
                Re: locals dxf <dxforth@gmail.com> - 2026-04-27 11:12 +1000
                Re: locals Hans Bezemer <the.beez.speaks@gmail.com> - 2026-04-28 14:34 +0200
                Re: locals Hans Bezemer <the.beez.speaks@gmail.com> - 2026-04-28 14:34 +0200
                Re: locals Gerry Jackson <do-not-use@swldwa.uk> - 2026-04-29 12:44 +0100
                Re: locals Hans Bezemer <the.beez.speaks@gmail.com> - 2026-04-29 14:37 +0200
                Re: locals Hans Bezemer <the.beez.speaks@gmail.com> - 2026-04-29 14:44 +0200
                Re: locals Paul Rubin <no.email@nospam.invalid> - 2026-05-01 23:50 -0700
                Re: locals anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2026-05-02 10:34 +0000
                Re: locals Paul Rubin <no.email@nospam.invalid> - 2026-05-01 23:54 -0700
                Re: locals dxf <dxforth@gmail.com> - 2026-05-02 17:36 +1000
                Re: locals Paul Rubin <no.email@nospam.invalid> - 2026-05-02 01:11 -0700
                Re: locals anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2026-05-02 15:58 +0000
      Re: Coroutines in Forth Krishna Myneni <krishna.myneni@ccreweb.org> - 2026-04-07 09:28 -0500
        Re: Coroutines in Forth anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2026-04-07 16:12 +0000
          Re: Coroutines in Forth Krishna Myneni <krishna.myneni@ccreweb.org> - 2026-04-07 18:06 -0500
          Re: Coroutines in Forth Gerry Jackson <do-not-use@swldwa.uk> - 2026-04-08 11:43 +0100
            Re: Coroutines in Forth albert@spenarnc.xs4all.nl - 2026-04-08 13:16 +0200
              Re: Coroutines in Forth Krishna Myneni <krishna.myneni@ccreweb.org> - 2026-04-08 11:47 -0500
                Re: Coroutines in Forth Gerry Jackson <do-not-use@swldwa.uk> - 2026-04-08 21:48 +0100
                Re: Coroutines in Forth Krishna Myneni <krishna.myneni@ccreweb.org> - 2026-04-09 07:06 -0500
                Re: Coroutines in Forth albert@spenarnc.xs4all.nl - 2026-04-09 16:41 +0200
                Re: Coroutines in Forth Krishna Myneni <krishna.myneni@ccreweb.org> - 2026-04-09 13:34 -0500
                Re: Coroutines in Forth albert@spenarnc.xs4all.nl - 2026-04-10 01:23 +0200
                Re: Coroutines in Forth Krishna Myneni <krishna.myneni@ccreweb.org> - 2026-04-09 21:34 -0500
                Re: Coroutines in Forth albert@spenarnc.xs4all.nl - 2026-04-09 13:01 +0200
                Re: Coroutines in Forth Krishna Myneni <krishna.myneni@ccreweb.org> - 2026-04-09 07:01 -0500
                Re: Coroutines in Forth albert@spenarnc.xs4all.nl - 2026-04-09 16:10 +0200
                Re: Coroutines in Forth Krishna Myneni <krishna.myneni@ccreweb.org> - 2026-04-09 13:29 -0500
              Re: Coroutines in Forth Gerry Jackson <do-not-use@swldwa.uk> - 2026-04-08 21:26 +0100
          Re: Coroutines in Forth Hans Bezemer <the.beez.speaks@gmail.com> - 2026-04-08 14:22 +0200
          Re: Coroutines in Forth Hans Bezemer <the.beez.speaks@gmail.com> - 2026-04-28 15:31 +0200
            Re: Coroutines in Forth albert@spenarnc.xs4all.nl - 2026-04-29 10:49 +0200
              Re: Coroutines in Forth Hans Bezemer <the.beez.speaks@gmail.com> - 2026-04-29 15:22 +0200
        Re: Coroutines in Forth Gerry Jackson <do-not-use@swldwa.uk> - 2026-04-08 11:33 +0100
          Re: Coroutines in Forth albert@spenarnc.xs4all.nl - 2026-04-08 13:07 +0200
            Re: Coroutines in Forth Gerry Jackson <do-not-use@swldwa.uk> - 2026-04-08 22:05 +0100
  Re: Coroutines in Forth albert <albert@spenarnc.xs4all.nl> - 2026-06-21 01:26 +0200

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