Re: Is this example in the Forth200x draft 11.1 correct?

From	anton@mips.complang.tuwien.ac.at (Anton Ertl)
Newsgroups	comp.lang.forth
Subject	Re: Is this example in the Forth200x draft 11.1 correct?
Date	2012-08-07 14:18 +0000
Organization	Institut fuer Computersprachen, Technische Universitaet Wien
Message-ID	<2012Aug7.161823@mips.complang.tuwien.ac.at> (permalink)
References	<jvhbrh$ca8$1@speranza.aioe.org> <abdc063b-a1be-4839-8724-cd10f8fa37b8@nc9g2000pbc.googlegroups.com> <jvqlka$79p$1@speranza.aioe.org>

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"Rod Pemberton" <do_not_have@notemailnot.cmm> writes:
>How do you implement CONSTANT VALUE DEFER SET etc without
>CREATE ... DOES> ?

Gforth has run-time routines DOCON DOVALUE DODEFER that are faster
than DODOES followed by Forth code.  Gforth also has an intelligent
COMPILE, that looks at the type of a word and compiles the appropriate
code.  In particular, when COMPILE, sees a constant, it compiles the
value of the constant:

5 constant x  ok
: foo x ;  ok
see foo 
: foo  
  5 ; ok

That's why DOVALUE is different from DOCON; compiling the then-current
value of the VALUE would be wrong.

There is a potential fundamental inefficiency in CREATE..DOES>-defined
words: Any implementation has to cater for the ability to modify the
data.  Consider:

: constant create , does> @ ;
5 constant x
: foo x ;

Here the compiler must not compile FOO into : FOO 5 ; because the user
could then do

6 ' x >body ! foo .

and that would have to print 6, not 5.  So the best that can be done
with CREATE...DOES> is to compile FOO to

: foo [ ' x >body ] literal @ ;

Of course, if the data is intended to be mutable, as for VALUE and
DEFER, you have to do it anyway and there is no fundamental
inefficiency.

Although, DEFERred words used for indirect recursion are not intended
to be mutable after the first IS.  If there was a way to communicate
such information to the Forth system, it could compile code more
efficiently.

- 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 2012: http://www.euroforth.org/ef12/

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Is this example in the Forth200x draft 11.1 correct? "Rod Pemberton" <do_not_have@notemailnot.cmm> - 2012-08-03 16:23 -0400
  Is this example in the Forth200x draft 11.1 correct? Mark Wills <markrobertwills@yahoo.co.uk> - 2012-08-03 13:49 -0700
  Re: Is this example in the Forth200x draft 11.1 correct? Bernd Paysan <bernd.paysan@gmx.de> - 2012-08-03 23:07 +0200
    Re: Is this example in the Forth200x draft 11.1 correct? "Rod Pemberton" <do_not_have@notemailnot.cmm> - 2012-08-03 18:28 -0400
      Re: Is this example in the Forth200x draft 11.1 correct? Bernd Paysan <bernd.paysan@gmx.de> - 2012-08-04 02:49 +0200
        Re: Is this example in the Forth200x draft 11.1 correct? "Rod Pemberton" <do_not_have@notemailnot.cmm> - 2012-08-04 04:33 -0400
          Re: Is this example in the Forth200x draft 11.1 correct? Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-08-04 04:37 -0500
  Re: Is this example in the Forth200x draft 11.1 correct? Hugh Aguilar <hughaguilar96@yahoo.com> - 2012-08-06 21:27 -0700
    Re: Is this example in the Forth200x draft 11.1 correct? Howerd <howerdo@yahoo.co.uk> - 2012-08-07 00:04 -0700
    Re: Is this example in the Forth200x draft 11.1 correct? "Rod Pemberton" <do_not_have@notemailnot.cmm> - 2012-08-07 05:05 -0400
      Re: Is this example in the Forth200x draft 11.1 correct? anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-08-07 14:18 +0000
        Re: Is this example in the Forth200x draft 11.1 correct? Alex McDonald <blog@rivadpm.com> - 2012-08-07 09:39 -0700
          Re: Is this example in the Forth200x draft 11.1 correct? Bernd Paysan <bernd.paysan@gmx.de> - 2012-08-07 20:20 +0200
            Re: Is this example in the Forth200x draft 11.1 correct? Alex McDonald <blog@rivadpm.com> - 2012-08-07 12:31 -0700
              Re: Is this example in the Forth200x draft 11.1 correct? Alex McDonald <blog@rivadpm.com> - 2012-08-07 13:26 -0700
                Re: Is this example in the Forth200x draft 11.1 correct? Bernd Paysan <bernd.paysan@gmx.de> - 2012-08-08 00:49 +0200
            Re: Is this example in the Forth200x draft 11.1 correct? Alex McDonald <blog@rivadpm.com> - 2012-08-07 12:33 -0700
          Re: Is this example in the Forth200x draft 11.1 correct? anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-08-08 07:21 +0000
          Re: Is this example in the Forth200x draft 11.1 correct? Mark Wills <markrobertwills@yahoo.co.uk> - 2012-08-08 01:12 -0700
            Re: Is this example in the Forth200x draft 11.1 correct? Bernd Paysan <bernd.paysan@gmx.de> - 2012-08-08 19:11 +0200
        Re: Is this example in the Forth200x draft 11.1 correct? Hugh Aguilar <hughaguilar96@yahoo.com> - 2012-08-07 19:29 -0700
        Re: Is this example in the Forth200x draft 11.1 correct? Elizabeth D Rather <erather@forth.com> - 2012-08-07 22:01 -0500
          Re: Is this example in the Forth200x draft 11.1 correct? Hugh Aguilar <hughaguilar96@yahoo.com> - 2012-08-07 20:07 -0700
            Re: Is this example in the Forth200x draft 11.1 correct? Elizabeth D Rather <erather@forth.com> - 2012-08-07 23:03 -0500
          Re: Is this example in the Forth200x draft 11.1 correct? anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-08-08 07:42 +0000
            Re: Is this example in the Forth200x draft 11.1 correct? Hugh Aguilar <hughaguilar96@yahoo.com> - 2012-08-08 18:12 -0700
              Re: Is this example in the Forth200x draft 11.1 correct? Hugh Aguilar <hughaguilar96@yahoo.com> - 2012-08-08 18:59 -0700
              Re: Is this example in the Forth200x draft 11.1 correct? Mark Wills <markrobertwills@yahoo.co.uk> - 2012-08-09 02:30 -0700
                Re: Is this example in the Forth200x draft 11.1 correct? anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-08-09 09:48 +0000
                Re: Is this example in the Forth200x draft 11.1 correct? Percy <percival.andrews@gmail.com> - 2012-08-10 06:33 -0700
                Re: Is this example in the Forth200x draft 11.1 correct? "David N. Williams" <williams@umich.edu> - 2012-08-10 09:58 -0400
                Re: Is this example in the Forth200x draft 11.1 correct? anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-08-10 15:39 +0000
                Re: Is this example in the Forth200x draft 11.1 correct? "David N. Williams" <williams@umich.edu> - 2012-08-10 16:15 -0400
                Re: Is this example in the Forth200x draft 11.1 correct? percival.andrews@gmail.com - 2012-08-10 16:42 -0700
                Re: Is this example in the Forth200x draft 11.1 correct? Coos Haak <chforth@hccnet.nl> - 2012-08-11 01:51 +0200
                Re: Is this example in the Forth200x draft 11.1 correct? George Hubert <georgeahubert@yahoo.co.uk> - 2012-08-11 06:25 -0700
                Re: Is this example in the Forth200x draft 11.1 correct? anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2012-08-11 09:12 +0000
                Re: Is this example in the Forth200x draft 11.1 correct? Hugh Aguilar <hughaguilar96@yahoo.com> - 2012-08-13 14:28 -0700
                Re: Is this example in the Forth200x draft 11.1 correct? Bernd Paysan <bernd.paysan@gmx.de> - 2012-08-14 00:51 +0200
                Re: Is this example in the Forth200x draft 11.1 correct? Hugh Aguilar <hughaguilar96@yahoo.com> - 2012-08-13 16:24 -0700
                Re: Is this example in the Forth200x draft 11.1 correct? Bernd Paysan <bernd.paysan@gmx.de> - 2012-08-14 03:25 +0200
                Re: Is this example in the Forth200x draft 11.1 correct? Hugh Aguilar <hughaguilar96@yahoo.com> - 2012-08-14 07:54 -0700
                Re: Is this example in the Forth200x draft 11.1 correct? Bernd Paysan <bernd.paysan@gmx.de> - 2012-08-14 23:22 +0200
                Re: Is this example in the Forth200x draft 11.1 correct? hughaguilar96@yahoo.com - 2012-08-16 00:37 -0700
      Re: Is this example in the Forth200x draft 11.1 correct? Hugh Aguilar <hughaguilar96@yahoo.com> - 2012-08-07 19:30 -0700

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