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Groups > comp.lang.forth > #4609

Re: multi-threading in Forth?

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Andrew Haley <andrew29@littlepinkcloud.invalid> writes:
> I think so.  There is the matter of whether, say, return stack
> manipulation is more useful than tail call optimization.  I'd choose
> tail call optimization every time, but IME code that (ab)uses the
> return stack for control flow is hard to understand and maintain.
> Whatever the problem, there's almost always a better way to do it than
> fiddling with the R-stack.

Can you elaborate on your IME?  I'm not being flippant; I'm privately
becoming more and more confident that fiddling with the return stack is
a huge readability and therefore maintainability win, so I'd appreciate
a course correction.

I recall that you prefer immediate words for a good subset of what
return-stack words can do.  E.g.,

  : with-base ( u -- )
    r> BASE @ >r swap BASE !
    ['] call catch r> BASE ! throw ;

  : base[ ( u -- )
    postpone BASE postpone @ postpone >r
    postpone BASE postpone ! ; immediate
  : ]base ( -- )
    postpone r> postpone BASE postpone ! ; immediate

  : x1 ( ... "to end of line" -- ... )
    16 with-base 0 parse evaluate ;

  : x2 ( ... "to end of line" -- ... )
    16 base[ 0 parse evaluate ]base ;

Return-stack access must be balanced after WITH-BASE and between BASE[
]BASE ; only WITH-BASE will reset the BASE if there's an exception
(maybe not desirable, but when it isn't WITH-BASE can be easily defined
to not do this).  In the presence of tail-call optimization, WITH-BASE
_can_ be used to do perverse things that only sometimes work

  : in-hex 16 with-base ;
  : x3 ( c-addr u -- )
    in-hex evaluate ;    \ only works if WITH-BASE was JMP'd to.

, but I oppose that.  You can take any feature too far.  You can have a
Forth word that accepts twenty arguments on the data stack.

But, these are so similar; how is only one of them hard to understand
and maintain?

Another class of return-stack words are words that validate some input:

  : -too-small ( c-addr u -- c-addr u | *returns from caller )
    dup 2 > ?exit 2drop r>drop ;
  : -not-forth ( c-addr u -- c-addr u | *returns from caller )
    2dup 2 - + 2 s" .f" compare(nc) 0= ?exit 2drop r>drop ;

  : .forth-file ( dirent-addr -- )
    USING dirent filename zcount
    -too-small -not-forth type space ;

"If it's not too small, and if it's not not forth, TYPE SPACE it."
Maybe S" .f" HAS-EXT; would be a better name, with the semicolon to
suggest the potential exit.

With immediate wordS:

  : -too-small ( c-addr u -- c-addr u | *exit )
    postpone dup 2 postpone literal postpone <=
    postpone if postpone 2drop postpone exit postpone then ; immediate

And so on.  It's used in exactly the same way, it has exactly the same
issue of "to test this, I need to use it within a temporary definition",
and it could be neater with a macro to replace the POSTPONEs.

So these are _exactly the same_.  How is the only of them hard to
understand and maintain?

I could have also "not done that" - have written

  : .forth-file ( dirent-addr -- )
    USING dirent filename zcount
    dup 2 <= if 2drop exit then
    2dup 2 - + 2 s" .f" compare(nc) if 2drop exit then
    type space ;

Or:

  : .forth-file ( dirent-addr -- )
    USING dirent filename zcount ( c-addr u )
    dup 2 > if  2dup 2 - + 2 s" .f" compare(nc) 0= if
      type space exit
    then then 2drop ;

Or:

  : .forth-file ( dirent-addr -- )
    USING dirent filename zcount 
    2dup long-enough? if 2dup is-forth? if
      type space exit
    then then 2drop ;

The last is nice and conventional, but is the return-stack version
really any harder to read?

Which classes of return-stack-fiddling word do you object to?

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Thread

multi-threading in Forth? Michael L Gassanenko <m_l_g3@yahoo.com> - 2011-08-02 02:01 -0700
  Re: multi-threading in Forth? mhx@iae.nl (Marcel Hendrix) - 2011-08-02 11:22 +0200
    Re: multi-threading in Forth? Zbiggy <zbigniew2011REMOVE@gmail.REMOVE.com> - 2011-08-02 15:26 +0200
    Re: multi-threading in Forth? mlg3 <m_l_g3@yahoo.com> - 2011-08-04 01:06 +0400
      Re: multi-threading in Forth? mhx@iae.nl (Marcel Hendrix) - 2011-08-04 06:36 +0200
        Re: multi-threading in Forth? Mark Wills <markrobertwills@yahoo.co.uk> - 2011-08-04 08:25 +0100
          Re: multi-threading in Forth? coos haak <chforth@hccnet.nl> - 2011-08-04 13:42 +0200
            Re: multi-threading in Forth? Zbiggy <zbigniew2011REMOVE@gmail.REMOVE.com> - 2011-08-04 14:35 +0200
              Re: multi-threading in Forth? Elizabeth D Rather <erather@forth.com> - 2011-08-04 08:30 -0500
                Re: multi-threading in Forth? Zbiggy <zbigniew2011REMOVE@gmail.REMOVE.com> - 2011-08-04 15:38 +0200
                Re: multi-threading in Forth? Elizabeth D Rather <erather@forth.com> - 2011-08-04 09:12 -0500
                Re: multi-threading in Forth? Mark Wills <markrobertwills@yahoo.co.uk> - 2011-08-04 16:50 +0100
                Re: multi-threading in Forth? mlg3 <m_l_g3@yahoo.com> - 2011-08-04 23:52 +0400
                Re: multi-threading in Forth? Andrew Haley <andrew29@littlepinkcloud.invalid> - 2011-08-05 08:50 -0500
                Re: multi-threading in Forth? Mark Wills <markrobertwills@yahoo.co.uk> - 2011-08-04 16:49 +0100
                Re: multi-threading in Forth? Zbiggy <zbigniew2011REMOVE@gmail.REMOVE.com> - 2011-08-04 19:23 +0200
                Re: multi-threading in Forth? Elizabeth D Rather <erather@forth.com> - 2011-08-05 10:57 -0500
              Re: multi-threading in Forth? stephenXXX@mpeforth.com (Stephen Pelc) - 2011-08-04 14:16 +0000
                Re: multi-threading in Forth? Mark Wills <markrobertwills@yahoo.co.uk> - 2011-08-04 16:51 +0100
                Re: multi-threading in Forth? stephenXXX@mpeforth.com (Stephen Pelc) - 2011-08-04 17:14 +0000
                Re: multi-threading in Forth? "Rod Pemberton" <do_not_have@noavailemail.cmm> - 2011-08-06 03:46 -0400
                Re: multi-threading in Forth? Zbiggy <zbigniew2011REMOVE@gmail.REMOVE.com> - 2011-08-04 19:11 +0200
                Re: multi-threading in Forth? Andrew Haley <andrew29@littlepinkcloud.invalid> - 2011-08-05 08:43 -0500
                Re: multi-threading in Forth? mlg3 <m_l_g3@yahoo.com> - 2011-08-06 01:49 +0400
                Re: multi-threading in Forth? Andrew Haley <andrew29@littlepinkcloud.invalid> - 2011-08-06 03:13 -0500
                Re: multi-threading in Forth? mlg3 <m_l_g3@yahoo.com> - 2011-08-09 04:41 +0400
                Re: multi-threading in Forth? mlg3 <m_l_g3@yahoo.com> - 2011-08-09 11:01 +0400
                Re: multi-threading in Forth? Andrew Haley <andrew29@littlepinkcloud.invalid> - 2011-08-10 09:02 -0500
                Re: multi-threading in Forth? mlg3 <m_l_g3@yahoo.com> - 2011-08-11 01:10 +0400
                Re: multi-threading in Forth? Ouatu Bogdan <ouatubi@gmail.com> - 2011-08-10 13:22 +0000
                Re: multi-threading in Forth? Zbiggy <zbigniew2011REMOVE@gmail.REMOVE.com> - 2011-08-06 01:12 +0200
                Re: multi-threading in Forth? coos haak <chforth@hccnet.nl> - 2011-08-06 02:37 +0200
                Re: multi-threading in Forth? Zbiggy <zbigniew2011REMOVE@gmail.REMOVE.com> - 2011-08-06 12:54 +0200
                Re: multi-threading in Forth? alextangent <blog@rivadpm.com> - 2011-08-06 12:15 +0100
                Re: multi-threading in Forth? Elizabeth D Rather <erather@forth.com> - 2011-08-05 22:23 -0500
                Re: multi-threading in Forth? Andrew Haley <andrew29@littlepinkcloud.invalid> - 2011-08-06 03:17 -0500
                Re: multi-threading in Forth? Julian Fondren <ayrnieu@gmail.com> - 2011-08-05 19:02 -0500
                Re: multi-threading in Forth? Andrew Haley <andrew29@littlepinkcloud.invalid> - 2011-08-06 04:01 -0500
                return-address manipulation (was: multi-threading in Forth?) anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2011-08-06 16:35 +0000
                Re: return-address manipulation Gerry Jackson <gerry@jackson9000.fsnet.co.uk> - 2011-08-07 11:45 +0100
                Re: return-address manipulation Josh Grams <josh@qualdan.com> - 2011-08-08 09:40 +0000
                Re: return-address manipulation Gerry Jackson <gerry@jackson9000.fsnet.co.uk> - 2011-08-08 12:17 +0100
                Re: return-address manipulation Josh Grams <josh@qualdan.com> - 2011-08-08 12:29 +0000
                Re: return-address manipulation mlg3 <m_l_g3@yahoo.com> - 2011-08-09 03:54 +0400
                Re: return-address manipulation mlg3 <m_l_g3@yahoo.com> - 2011-08-09 02:52 +0400
                Re: return-address manipulation Gerry Jackson <gerry@jackson9000.fsnet.co.uk> - 2011-08-09 20:54 +0100
                Re: return-address manipulation mlg3 <m_l_g3@yahoo.com> - 2011-08-11 09:00 +0400
                Re: return-address manipulation Andrew Haley <andrew29@littlepinkcloud.invalid> - 2011-08-09 14:49 -0500
                Re: return-address manipulation anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2011-08-10 09:03 +0000
                Re: return-address manipulation Andrew Haley <andrew29@littlepinkcloud.invalid> - 2011-08-10 05:13 -0500
                Re: return-address manipulation mlg3 <m_l_g3@yahoo.com> - 2011-08-11 09:24 +0400
                Re: return-address manipulation Andrew Haley <andrew29@littlepinkcloud.invalid> - 2011-08-11 04:09 -0500
                Re: return-address manipulation mlg3 <m_l_g3@yahoo.com> - 2011-08-11 09:36 +0400
                Re: return-address manipulation mlg3 <m_l_g3@yahoo.com> - 2011-08-11 09:54 +0400
                Re: return-address manipulation Andrew Haley <andrew29@littlepinkcloud.invalid> - 2011-08-11 04:16 -0500
                Re: multi-threading in Forth? Julian Fondren <ayrnieu@gmail.com> - 2011-08-07 01:43 -0500
                Re: multi-threading in Forth? Spam@ControlQ.com - 2011-08-06 12:36 -0400
                Re: multi-threading in Forth? Julian Fondren <ayrnieu@gmail.com> - 2011-08-07 01:13 -0500
                Re: multi-threading in Forth? mlg3 <m_l_g3@yahoo.com> - 2011-08-09 02:35 +0400
                Re: multi-threading in Forth? Albert van der Horst <albert@spenarnc.xs4all.nl> - 2011-08-07 10:08 +0000
                Re: multi-threading in Forth? Josh Grams <josh@qualdan.com> - 2011-08-07 13:45 +0000
                Re: multi-threading in Forth? mhx@iae.nl (Marcel Hendrix) - 2011-08-05 17:17 +0200
                Re: multi-threading in Forth? Zbiggy <zbigniew2011REMOVE@gmail.REMOVE.com> - 2011-08-05 19:23 +0200
                Re: multi-threading in Forth? Elizabeth D Rather <erather@forth.com> - 2011-08-05 10:53 -0500
                Re: multi-threading in Forth? Zbiggy <zbigniew2011REMOVE@gmail.REMOVE.com> - 2011-08-05 19:18 +0200
                Re: multi-threading in Forth? Elizabeth D Rather <erather@forth.com> - 2011-08-06 09:59 -0500
                Re: multi-threading in Forth? Spam@ControlQ.com - 2011-08-06 12:28 -0400
                Re: multi-threading in Forth? Albert van der Horst <albert@spenarnc.xs4all.nl> - 2011-08-06 11:29 +0000
            Re: multi-threading in Forth? Mark Wills <markrobertwills@yahoo.co.uk> - 2011-08-04 16:47 +0100
              Re: multi-threading in Forth? Julian Fondren <ayrnieu@gmail.com> - 2011-08-04 13:54 -0500
              Re: multi-threading in Forth? coos haak <chforth@hccnet.nl> - 2011-08-04 22:02 +0200
  Re: multi-threading in Forth? Elizabeth D Rather <erather@forth.com> - 2011-08-02 08:23 -0500
    Re: multi-threading in Forth? Zbiggy <zbigniew2011REMOVE@gmail.REMOVE.com> - 2011-08-02 15:30 +0200
      Re: multi-threading in Forth? Elizabeth D Rather <erather@forth.com> - 2011-08-02 08:53 -0500
        Re: multi-threading in Forth? Andrew Haley <andrew29@littlepinkcloud.invalid> - 2011-08-03 03:53 -0500

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