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Re: LOOP

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Am 07.07.2025 um 08:54 schrieb Gerry Jackson:
> On 03/07/2025 20:33, minforth wrote:
>> On Sat, 28 Jun 2025 21:01:48 +0000, Anton Ertl wrote:
>>
>>> sean@conman.org writes:
>>>>  What is the difference between FOR/NEXT and DO/LOOP?  Don't they do 
>>>> the
>>>> same thing?
>>>
>>> FOR ... NEXT on one system does not do the same thing as FOR ... NEXT
>>> on some other systems, and they all behave different from DO ... LOOP.
>>>
>>
>> Correct. Here are variants with iterators that even run on gforth 0.7.9:
>>
>> \ ====== <n> FOR# .. #TIMES
>> ==================================================
>> \ original: machine code
>> \ demo variant: slow Forth
>>
>> : _ITERATE \ end xt
>>      swap
>>      BEGIN dup 0>
>>      WHILE over execute 1-
>>      REPEAT 2drop ;
>>
>> : FOR# postpone [: ; IMMEDIATE
>>
>> : #TIMES postpone ;] postpone _iterate ; IMMEDIATE
>>
>> \ ====== <n> FOR .. N M .. NEXT
>> ==============================================
> 
> I've found looping quotations useful but I like to include the quotation 
> inside the loop e.g. (without the syntactic sugar and moving the 
> iterator inside the quotation):
> 
> : downcount begin [: dup 0> if dup . 1- then ;] over 0> while execute 
> repeat 2drop ;
> 10 downcount \ displays 10 9 8 7 6 5 4 3 2 1  ok
> 
> Advantages are:
> 1) The xt is not passed to the quotation and so doesn't get in the way. 
> 2) The xt is loaded as a literal when the quotation exits.
> 3) The quotation can exit the loop early by EXITing with 0 on the stack.

That's the nice thing about Forth: you can mould it to your taste. :-)

My initial motivation was that I wanted free access to the return
stack, and to kick UNLOOP out. From my slow playhorse Forth
(VM with address interpreter):

\ ------ Template: n FOR .. NEXT  and  adr n elsize FOR> .. NEXT
\ (negative elsize iterates backwards over array)
\ Primitives:
\ _ITERATE ( a n s xt -- ) M3 iterator (max. nesting depth 2)
\ N ( -- n ) N! ( n -- ) inner index in single FOR..NEXT loop
\ M ( -- n ) M! ( n -- ) inner index in nested FOR.FOR..NEXT.NEXT loops
: FOR>  postpone [: ; IMMEDIATE \ M3
: FOR 0 postpone literal postpone swap 1 postpone literal
	postpone for> ; IMMEDIATE \ M3
: NEXT postpone ;] postpone _iterate ; IMMEDIATE \ M3

Demo session:

+---------------------+
¦  Min3rd Core Forth  ¦
+---------------------+
1020048 bytes free
# : T1 10 FOR n . NEXT ;  ok
# t1 0 1 2 3 4 5 6 7 8 9  ok
: t4 10 FOR -111 >r n . r> drop NEXT ;  ok
# t4 0 1 2 3 4 5 6 7 8 9  ok
# : T2 pad 5 cell FOR> n u. NEXT ;  ok
# : T3 pad 5 cell negate FOR> n u. NEXT ;  ok
# hex  ok
$ pad u. F7BD2F1C  ok
$ t2 F7BD2F1C F7BD2F20 F7BD2F24 F7BD2F28 F7BD2F2C  ok
$ t3 F7BD2F2C F7BD2F28 F7BD2F24 F7BD2F20 F7BD2F1C  ok
$ decimal  ok
# fload demo/for_next.m3
Benchmarking 1000000 loops:
DO..LOOP: 101.7 ms
FOR..NEXT: 26.5 ms ok
# : T5 3 FOR 7 >r 3 FOR 8 >r n . m . r> drop NEXT r> drop NEXT ;  ok
# t5 0 0 1 0 2 0 0 1 1 1 2 1 0 2 1 2 2 2  ok
#

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OOS approach revisited zbigniew2011@gmail.com (LIT) - 2025-06-23 05:09 +0000
  Re: OOS approach revisited dxf <dxforth@gmail.com> - 2025-06-24 23:28 +1000
    Re: OOS approach revisited zbigniew2011@gmail.com (LIT) - 2025-06-26 17:27 +0000
      Re: OOS approach revisited minforth@gmx.net (minforth) - 2025-06-27 02:16 +0000
        Re: OOS approach revisited dxf <dxforth@gmail.com> - 2025-06-27 17:29 +1000
          Re: OOS approach revisited minforth <minforth@gmx.net> - 2025-06-27 11:49 +0200
            Re: OOS approach revisited zbigniew2011@gmail.com (LIT) - 2025-06-27 16:55 +0000
              Re: OOS approach revisited albert@spenarnc.xs4all.nl - 2025-06-27 20:15 +0200
                Re: OOS approach revisited minforth <minforth@gmx.net> - 2025-06-27 22:35 +0200
                Re: OOS approach revisited albert@spenarnc.xs4all.nl - 2025-06-28 11:34 +0200
                Re: OOS approach revisited Stephen Pelc <stephen@vfxforth.com> - 2025-06-28 09:37 +0000
              Re: OOS approach revisited dxf <dxforth@gmail.com> - 2025-06-28 12:03 +1000
            LOOP (was: OOS approach revisited) anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2025-06-28 10:23 +0000
              Re: LOOP (was: OOS approach revisited) albert@spenarnc.xs4all.nl - 2025-06-28 14:26 +0200
              Re: LOOP dxf <dxforth@gmail.com> - 2025-06-28 22:41 +1000
                Re: LOOP sean@conman.org - 2025-06-28 20:04 +0000
                Re: LOOP anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2025-06-28 21:01 +0000
                Re: LOOP minforth@gmx.net (minforth) - 2025-07-03 19:33 +0000
                Re: LOOP Gerry Jackson <do-not-use@swldwa.uk> - 2025-07-07 07:54 +0100
                Re: LOOP minforth <minforth@gmx.net> - 2025-07-07 10:46 +0200
                Re: LOOP dxf <dxforth@gmail.com> - 2025-06-29 13:04 +1000
              Re: LOOP (was: OOS approach revisited) anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2025-06-28 16:04 +0000
        DO..LOOP and stack shuffling (was: OOS approach revisited) anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2025-06-28 17:46 +0000
          Re: DO..LOOP and stack shuffling Hans Bezemer <the.beez.speaks@gmail.com> - 2025-07-01 13:53 +0200
            Re: DO..LOOP and stack shuffling dxf <dxforth@gmail.com> - 2025-07-03 13:59 +1000
            Re: DO..LOOP and stack shuffling anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2025-07-03 07:50 +0000
        Re: OOS approach revisited Hans Bezemer <the.beez.speaks@gmail.com> - 2025-06-30 15:43 +0200
      Re: OOS approach revisited dxf <dxforth@gmail.com> - 2025-06-27 13:39 +1000

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