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Re: CfV: Quotations

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Bernd Paysan <bernd.paysan@gmx.de> writes:
>Am Sun, 21 Aug 2016 09:32:58 +0000 schrieb Anton Ertl:
>
>> Ok, so your solution is to have one global variable, and access all the
>> other data through that.  I very much doubt that is sufficient, because
>> global variables are not sufficient to implement nested Pascal's and GNU
>> C's nested functions, either; instead, they do static link chains and
>> trampolines.  E.g, I don't think you can do the man-or-boy-test with
>> that.
>
>Well, the boy-or-man test isn't really needing better quotations, it's 
>needing a bit more OOP.

Sure, you can implement the functionality in some way in any
Touring-complete language.  But the original test was for whether
nested functions in Algol 60 were correctly implemented.  So if it can
be implemented with closures (actually Pascal function parameters are
sufficient), but not with the proposed quotations, it shows that
passing data on the stack does not replace non-local data accesses in
every case.  Of course, as is often the case in Forth, the question is
if the various approaches for avoiding a feature are sufficient to
make that feature unnecessary or not.

>require mini-oof2.fs
>
>\ define a class for the default values
>
>object class
>    field: k
>    method b
>end-class mob
>
>:noname ( -- n ) k @ ; mob to b
>mob new constant m-1  -1 m-1 .k !
>mob new constant m0    0 m0 .k !
>mob new constant m1    1 m1 .k !
>
>\ define a class for the context
>
>mob class
>    field: x1
>    field: x2
>    field: x3
>    field: x4
>    field: x5
>end-class b-ctx
>
>: a ( k x1 x2 x3 x4 x5 -- result )
>    b-ctx new >o
>    x5 ! x4 ! x3 ! x2 ! x1 ! k !
>    k @ 0<= IF
>	x4 @ .b x5 @ .b +
>    ELSE
>	b
>    THEN
>    dispose o> ;
>
>:noname ( -- n )
>    -1 k +!
>    k @ o x1 @ x2 @ x3 @ x4 @ a
>; b-ctx to b
>
>: a-n ( n -- n' )
>    m1 m-1 m-1 m1 m0 a ;

For comparsion, here's the Algol 60 variant:

begin
  real procedure A(k, x1, x2, x3, x4, x5);
  value k; integer k;
  begin
    real procedure B;
    begin k := k - 1;
          B := A := A(k, B, x1, x2, x3, x4);
    end;
    if k <= 0 then A := x4 + x5 else B;
  end;
  outreal(A(10, 1, -1, -1, 1, 0));
end;

and my attempt at a version in Forth with access to outer locals,
based on <http://rosettacode.org/wiki/Man_or_boy_test#Pascal> (my
Algol 60 is not good enough to grasp the fine details of the Algol 60
version):

0 constant zero
1 constant one
-1 constant negone

: A {: k x1 x2 x3 x4 x5 | B -- n :} recursive
  [: k 1- to k
     k B x1 x2 x3 x4 A ;] to B
  k 0 <= if
    x4 execute x5 execute +
  else
    B execute
  then ;

10 ' one ' negone ' negone ' one ' zero A .

So access to outer locals makes this quite a bit shorter (14 instead
of 41 lines) than making the frames explicit by coding them in OOP.

The question is how often that helps for real-world programs.  My
guess is that, with the Pascal-like restriction, not often enough to
make it worthwhile.  With garbage-collection of closures, it would
probably be worthwhile, but we probably don't want to go there; and
for something in between, we will have to see.

- 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 2016: http://www.euroforth.org/ef16/

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CfV: Quotations anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-08-10 16:52 +0000
  Re: CfV: Quotations Matthias Trute <matthias.trute@gmail.com> - 2016-08-10 11:19 -0700
  Re: CfV: Quotations Paul Rubin <no.email@nospam.invalid> - 2016-08-10 11:55 -0700
    Re: CfV: Quotations Bernd Paysan <bernd.paysan@gmx.de> - 2016-08-14 20:52 +0000
      Re: CfV: Quotations hughaguilar96@gmail.com - 2016-08-14 14:42 -0700
        Re: CfV: Quotations Julian Fondren <julian.fondren@gmail.com> - 2016-08-14 16:43 -0700
      Re: CfV: Quotations Paul Rubin <no.email@nospam.invalid> - 2016-08-15 22:16 -0700
        Re: CfV: Quotations anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-08-16 07:13 +0000
          Re: CfV: Quotations Paul Rubin <no.email@nospam.invalid> - 2016-08-18 15:30 -0700
            Re: CfV: Quotations anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-08-19 15:32 +0000
          Re: CfV: Quotations Bernd Paysan <bernd.paysan@gmx.de> - 2016-08-20 20:46 +0000
            Re: CfV: Quotations anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-08-21 09:32 +0000
              Re: CfV: Quotations hughaguilar96@gmail.com - 2016-08-21 11:06 -0700
                Re: CfV: Quotations anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-08-24 17:02 +0000
              Re: CfV: Quotations Bernd Paysan <bernd.paysan@gmx.de> - 2016-08-21 22:52 +0000
                Re: CfV: Quotations anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-08-22 13:54 +0000
                Re: CfV: Quotations Bernd Paysan <bernd.paysan@gmx.de> - 2016-08-22 23:19 +0000
                Re: CfV: Quotations anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-08-24 15:54 +0000
                Re: CfV: Quotations Bernd Paysan <bernd@net2o.de> - 2016-08-28 00:43 +0000
                Re: CfV: Quotations anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-08-28 09:53 +0000
                Re: CfV: Quotations Andrew Haley <andrew29@littlepinkcloud.invalid> - 2016-08-28 08:32 -0500
                Re: CfV: Quotations anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-08-28 14:38 +0000
  Re: CfV: Quotations mhx@iae.nl - 2016-08-10 12:02 -0700
  Re: CfV: Quotations Gerry Jackson <gerry@jackson9000.fsnet.co.uk> - 2016-08-11 17:25 +0100
  Re: CfV: Quotations Julian Fondren <julian.fondren@gmail.com> - 2016-08-11 12:48 -0700
  Re: CfV: Quotations minforth@arcor.de - 2016-08-16 03:31 -0700
  Re: CfV: Quotations Gerry Jackson <gerry@jackson9000.fsnet.co.uk> - 2016-08-31 15:15 +0100
    Re: CfV: Quotations anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-08-31 15:26 +0000
      Re: CfV: Quotations Gerry Jackson <gerry@jackson9000.fsnet.co.uk> - 2016-09-02 22:33 +0100
        Re: CfV: Quotations anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-09-03 06:47 +0000

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