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Groups > comp.lang.forth > #11913

Re: Distinguishing DOES>

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Andrew Haley <andrew29@littlepinkcloud.invalid> writes:
>Assuming a fairly conventional threaded implementation, <BUILDS wastes
>a cell, CREATE doesn't.

You are comparing two different implementation techniques for DOES>
(or, in colloquial English, you are comparing apples and oranges).
For context, consider this example:

: constant <builds , does> ( handler ) @ ;
5 constant foo

The two implementation techniques are:

1) The header of FOO looks as follows:

Name field, link field
dodoes (code field)
handler (points where HANDLER is in the code above)
5      (data)

Here we have DODOES to know how to treat the word on the machine code
level and HANDLER to find the high-level code.

2) The header of FOO looks as follows:

Name field, link field
handler-5 (or so)
5

and at HANDLER-5 we have

jsr dodoes (or somesuch)

Here the JSR pushes HANDLER on the return stack and DODOES finds it
there.


Using the first technique with CREATE would mean that every CREATEd
word would need cell containing the handler, just in case a DOES>
comes along.  Therefore, people introduced BUILDS> so that they would
not have this overhead for other CREATEd words.  So, if you use that
technique, letting DOES> work with CREATE (instead of just with
<BUILDS) costs an extra cell for every DOES>-less created word.

With the second technique <BUILDS is just the same as CREATE, so
<BUILDS was left away in systems employing this technique.

>CREATE replaced <BUILDS in DOES> words for
>that reason: it's a superior implementation technique.

You mean that the second technique above is superior.  For some
settings that is the case, for others it isn't (e.g., Gforth uses
technique 1, and there are good reasons for that; and every code field
has an extra cell).  In any case, the second implementation technique
is completely compatible with <BUILDS, just define

: <BUILDS CREATE ;

- 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 2011: http://www.euroforth.org/ef11/

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Distinguishing DOES> JennyB <jennybrien@googlemail.com> - 2012-05-03 08:59 -0700
  Re: Distinguishing DOES> Hugh Aguilar <hughaguilar96@yahoo.com> - 2012-05-03 17:23 -0700
    Re: Distinguishing DOES> Zbiggy <zbigniew2011REMOVE@gmail.REMOVE.com> - 2012-05-04 10:47 +0100
      Re: Distinguishing DOES> Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-05-04 05:12 -0500
        Re: Distinguishing DOES> anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-05-04 11:33 +0000
          Re: Distinguishing DOES> Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-05-04 08:11 -0500
            Re: Distinguishing DOES> anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-05-04 16:18 +0000
              Re: Distinguishing DOES> Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-05-05 02:02 -0500
                Re: Distinguishing DOES> anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-05-05 14:16 +0000
                Re: Distinguishing DOES> Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-05-06 02:53 -0500
                Re: Distinguishing DOES> anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-05-05 14:25 +0000
                Re: Distinguishing DOES> BruceMcF <agila61@netscape.net> - 2012-05-05 08:07 -0700
                Re: Distinguishing DOES> Hugh Aguilar <hughaguilar96@yahoo.com> - 2012-05-08 06:23 -0700
                Re: Distinguishing DOES> Bernd Paysan <bernd.paysan@gmx.de> - 2012-05-09 00:25 +0200
                Re: Distinguishing DOES> Hugh Aguilar <hughaguilar96@yahoo.com> - 2012-05-09 01:26 -0700
                Re: Distinguishing DOES> Mark Wills <markrobertwills@yahoo.co.uk> - 2012-05-09 03:18 -0700
                Re: Distinguishing DOES> Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-05-09 05:29 -0500
                Re: Distinguishing DOES> "Elizabeth D. Rather" <erather@forth.com> - 2012-05-09 07:11 -1000
                Re: Distinguishing DOES> Zbiggy <zbigniew2011REMOVE@gmail.REMOVE.com> - 2012-05-09 22:48 +0100
                Re: Distinguishing DOES> Bernd Paysan <bernd.paysan@gmx.de> - 2012-05-09 23:22 +0200
                Re: Distinguishing DOES> Zbiggy <zbigniew2011REMOVE@gmail.REMOVE.com> - 2012-05-09 23:43 +0100
                Re: Distinguishing DOES> Bernd Paysan <bernd.paysan@gmx.de> - 2012-05-10 00:49 +0200
                Re: Distinguishing DOES> Zbiggy <zbigniew2011REMOVE@gmail.REMOVE.com> - 2012-05-10 11:33 +0100
                Re: Distinguishing DOES> Albert van der Horst <albert@spenarnc.xs4all.nl> - 2012-05-10 10:02 +0000
                Re: Distinguishing DOES> Bernd Paysan <bernd.paysan@gmx.de> - 2012-05-10 15:13 +0200
                Re: Distinguishing DOES> Mark Wills <markrobertwills@yahoo.co.uk> - 2012-05-10 05:07 -0700
                Re: Distinguishing DOES> Hugh Aguilar <hughaguilar96@yahoo.com> - 2012-05-10 22:57 -0700
  Re: Distinguishing DOES> Albert van der Horst <albert@spenarnc.xs4all.nl> - 2012-05-04 12:37 +0000
  Re: Distinguishing DOES> Doug Hoffman <glidedog@gmail.com> - 2012-05-04 10:14 -0400
    Re: Distinguishing DOES> humptydumpty <ouatubi@gmail.com> - 2012-05-04 20:27 +0000
      Re: Distinguishing DOES> Doug Hoffman <glidedog@gmail.com> - 2012-05-05 06:16 -0400
        Re: Distinguishing DOES> JennyB <jennybrien@googlemail.com> - 2012-05-05 07:19 -0700
          Re: Distinguishing DOES> anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-05-05 14:55 +0000
            Re: Distinguishing DOES> JennyB <jennybrien@googlemail.com> - 2012-05-07 07:24 -0700
          Re: Distinguishing DOES> Albert van der Horst <albert@spenarnc.xs4all.nl> - 2012-05-06 11:04 +0000
          Re: Distinguishing DOES> Doug Hoffman <glidedog@gmail.com> - 2012-05-06 07:47 -0400
        Re: Distinguishing DOES> ward@megawolf.com - 2012-05-08 04:39 -0700
          Re: Distinguishing DOES> Doug Hoffman <glidedog@gmail.com> - 2012-05-08 07:50 -0400
  Re: Distinguishing DOES> Hans Bezemer <the.beez.speaks@gmail.com> - 2012-05-05 14:24 +0200
    Re: Distinguishing DOES> Albert van der Horst <albert@spenarnc.xs4all.nl> - 2012-05-06 11:09 +0000

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