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Re: The extended Eaker-Pelc CASE as general control structure

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Anton Ertl wrote:
> "HAA" <someone@microsoft.com> writes:
> >Anton Ertl wrote:
> ...
> Actually multi-exit loops are not that rare; every search loop has
> multiple exits: one for the search and the other for reaching the end
> of the search space.

That's 2 exits.  One or two exits are commonplace.  Nobody uses CASE
when there is one or two exits because they know it's overkill.

MPE's NEXTCASE has been around for a decade or more yet AFAIK no
other Forth has bothered to implement it.  What does that tell you about
the practical need for such a thing.

> >: gcd ( n1 n2 -- n )
> >    begin begin
> >        2dup > while  tuck - again  then
> >        2dup < while  over - again  then
> >    drop ;
>
> Cute.

Cute because the code is near identical to yours *without* any extensions.

> >: collatz ( u -- )
> >    \ print the 3n+1 sequence starting at u until we reach 1
> >    begin begin
> >        dup .
> >        1 over = if  drop exit  then
> >        dup 1 and while  3 * 1+ again  then
> >        2/
> >    again ;
>
> : collatz ( u -- )
>   begin
>     begin
>       dup .
>       dup 1 = if
>         drop exit then
>       dup 1 and while
>         3 * 1+
>     repeat
>     2/
>   again ;
>
> But here we already use EXIT (making common code afterwards
> cumbersome), because we cannot use WHILE in that spot to jump behind
> the AGAIN.

I didn't choose the example.  EXIT is perfectly fine here.

Your problem is finding a loop example that justifies the CASE extensions.
The example has to be simple enough that factoring it out is not justified,
but not so simple that existing techniques can be used to solve it.
I doubt such an example exists because none have come to light in
40+ years of Forth.

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The extended Eaker-Pelc CASE as general control structure anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-02-06 18:15 +0000
  Re: The extended Eaker-Pelc CASE as general control structure JennyB <jennybrien@googlemail.com> - 2016-02-07 03:57 -0800
    Re: The extended Eaker-Pelc CASE as general control structure anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-02-08 12:59 +0000
      Re: The extended Eaker-Pelc CASE as general control structure JennyB <jennybrien@googlemail.com> - 2016-02-08 09:48 -0800
        Re: The extended Eaker-Pelc CASE as general control structure anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-02-08 18:10 +0000
          Re: The extended Eaker-Pelc CASE as general control structure JennyB <jennybrien@googlemail.com> - 2016-02-09 14:02 -0800
            Short-circuit evaluation (was: The extended Eaker-Pelc CASE ...) anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-02-10 16:10 +0000
  Re: The extended Eaker-Pelc CASE as general control structure "WJ" <w_a_x_man@yahoo.com> - 2016-02-07 14:32 +0000
  Re: The extended Eaker-Pelc CASE as general control structure "WJ" <w_a_x_man@yahoo.com> - 2016-02-07 14:53 +0000
    Re: The extended Eaker-Pelc CASE as general control structure Albert van der Horst <albert@spenarnc.xs4all.nl> - 2016-02-07 15:56 +0000
      Re: The extended Eaker-Pelc CASE as general control structure stephen@mpeforth.com (Stephen Pelc) - 2016-02-07 18:11 +0000
        Re: The extended Eaker-Pelc CASE as general control structure "HAA" <someone@microsoft.com> - 2016-02-08 12:04 +1100
          Re: The extended Eaker-Pelc CASE as general control structure stephen@mpeforth.com (Stephen Pelc) - 2016-02-08 10:29 +0000
            Re: The extended Eaker-Pelc CASE as general control structure anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-02-08 11:00 +0000
              Re: The extended Eaker-Pelc CASE as general control structure stephen@mpeforth.com (Stephen Pelc) - 2016-02-08 12:28 +0000
                Re: The extended Eaker-Pelc CASE as general control structure anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-02-08 15:26 +0000
                Re: The extended Eaker-Pelc CASE as general control structure stephen@mpeforth.com (Stephen Pelc) - 2016-02-08 16:16 +0000
                Re: The extended Eaker-Pelc CASE as general control structure anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-02-08 16:37 +0000
                Re: The extended Eaker-Pelc CASE as general control structure anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-02-08 16:21 +0000
            Re: The extended Eaker-Pelc CASE as general control structure "HAA" <someone@microsoft.com> - 2016-02-11 21:12 +1100
              Re: The extended Eaker-Pelc CASE as general control structure stephen@mpeforth.com (Stephen Pelc) - 2016-02-11 10:46 +0000
      Re: The extended Eaker-Pelc CASE as general control structure JennyB <jennybrien@googlemail.com> - 2016-02-07 12:33 -0800
        Re: The extended Eaker-Pelc CASE as general control structure stephen@mpeforth.com (Stephen Pelc) - 2016-02-08 10:38 +0000
  Re: The extended Eaker-Pelc CASE as general control structure "HAA" <someone@microsoft.com> - 2016-02-08 12:07 +1100
    Re: The extended Eaker-Pelc CASE as general control structure anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-02-08 11:11 +0000
      Re: The extended Eaker-Pelc CASE as general control structure Albert van der Horst <albert@spenarnc.xs4all.nl> - 2016-02-08 14:49 +0000
      Re: The extended Eaker-Pelc CASE as general control structure "HAA" <someone@microsoft.com> - 2016-02-09 20:31 +1100
        Re: The extended Eaker-Pelc CASE as general control structure hughaguilar96@gmail.com - 2016-02-09 12:38 -0800
      Re: The extended Eaker-Pelc CASE as general control structure "WJ" <w_a_x_man@yahoo.com> - 2016-02-11 14:23 +0000
        Re: The extended Eaker-Pelc CASE as general control structure "WJ" <w_a_x_man@yahoo.com> - 2016-02-11 19:45 +0000

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