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Groups > comp.lang.forth > #44655

Re: Is WHILE allowed within DO .. LOOP ?

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Andrew Haley <andrew29@littlepinkcloud.invalid> writes:
>JennyB <jennybrien@googlemail.com> wrote:
>
>> This is not meant to be portable. It only works if do-sys happens to
>> be the right size.
>> 
>> It's also needlessly complex. The cleaner (and portable) way to do
>> this sort of thing is:
>> 
>>     DO
>>          IF ... UNLOOP EXIT THEN
>>        ...
>>     LOOP
>>     ...
>> 
>>     ;
>
>The caller usually needs to know whether the loop was exited early.
>So, the above would likely be
>
>: barf ( - t)
>     do
>          if ... unloop true ( we found something)  exit then
>        ...
>     loop
>     ...
> 
>     false ( we didn't find anything) ;
>
>and the caller would have to do 
>
>     barf if  found-action  else  not-found-action  then
>
>I hate passing flags around like that. I prefer
>
>    do  ... 
>        while
>        ... 
>    loop
>        not-found-action
>    else
>        found-action  unloop
>    then

Or you can write it in standard Forth as

do
  ... if ... found-action unloop exit then
  ... loop
not-found-action

In any case, the word that spawned this discussion actually returns
true or false, so the technique you defend here does not prevent that.

It also and has no control flow join in the end, so it could be
converted into standard Forth without any drawback.  Makes me wonder
why it was written in this way in the first place.

- anton
-- 
M. Anton Ertl  http://www.complang.tuwien.ac.at/anton/home.html
comp.lang.forth FAQs: http://www.complang.tuwien.ac.at/forth/faq/toc.html
     New standard: http://www.forth200x.org/forth200x.html
   EuroForth 2015: http://www.rigwit.co.uk/EuroForth2015/

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Is WHILE allowed within DO .. LOOP ? Albert van der Horst <albert@spenarnc.xs4all.nl> - 2016-01-06 16:28 +0000
  Re: Is WHILE allowed within DO .. LOOP ? Gerry Jackson <gerry@jackson9000.fsnet.co.uk> - 2016-01-06 17:20 +0000
  Is WHILE allowed within DO .. LOOP ? JennyB <jennybrien@googlemail.com> - 2016-01-06 09:24 -0800
    Re: Is WHILE allowed within DO .. LOOP ? Andrew Haley <andrew29@littlepinkcloud.invalid> - 2016-01-06 16:06 -0600
      Re: Is WHILE allowed within DO .. LOOP ? anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-01-07 08:36 +0000
        Re: Is WHILE allowed within DO .. LOOP ? Albert van der Horst <albert@spenarnc.xs4all.nl> - 2016-01-07 13:13 +0000
          Re: Is WHILE allowed within DO .. LOOP ? anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-01-07 13:33 +0000
            Re: Is WHILE allowed within DO .. LOOP ? "Elizabeth D. Rather" <erather@forth.com> - 2016-01-07 18:42 -1000
              Re: Is WHILE allowed within DO .. LOOP ? anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-01-08 10:19 +0000
                Re: Is WHILE allowed within DO .. LOOP ? Bernd Paysan <bernd.paysan@gmx.de> - 2016-01-08 22:09 +0100
                Re: Is WHILE allowed within DO .. LOOP ? anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-01-09 16:51 +0000
                Re: Is WHILE allowed within DO .. LOOP ? Bernd Paysan <bernd.paysan@gmx.de> - 2016-01-09 19:49 +0100
                Re: Is WHILE allowed within DO .. LOOP ? anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-01-10 15:44 +0000
              Re: Is WHILE allowed within DO .. LOOP ? Albert van der Horst <albert@spenarnc.xs4all.nl> - 2016-01-08 11:22 +0000
    Re: Is WHILE allowed within DO .. LOOP ? hughaguilar96@gmail.com - 2016-01-06 22:33 -0800
      Re: Is WHILE allowed within DO .. LOOP ? Raimond Dragomir <raimond.dragomir@gmail.com> - 2016-01-06 22:47 -0800
  Re: Is WHILE allowed within DO .. LOOP ? hughaguilar96@gmail.com - 2016-01-11 19:46 -0800
    Re: Is WHILE allowed within DO .. LOOP ? Raimond Dragomir <raimond.dragomir@gmail.com> - 2016-01-11 22:37 -0800

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