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Re: +TO in GForth

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On Wednesday, February 19, 2014 8:36:56 AM UTC-7, Anton Ertl wrote:
> Mark Wills <markrobertwills@yahoo.co.uk> writes:
> >How does one define +TO in GForth?
> 
> You don't!  Use variables if you update stuff frequently; and we have
> a word +! that helps there.
> 
> >I tried:
> 
> >: +to ( n tib:"value" -- ) ' >body dup >r @ + r> ! ; immediate
> 
> >Works in immediate mode, but doesn't work in a colon-def. Probably only works in ITC, too.
> 
> Why would you think that it only works in ITC?  And think about why it
> works interpretevely, but not compiled.
> 
> Let's refine your solution a little:
> 
> : +to-int ( n "value" -- ) ' >body +! ;
> 
> Note that the IMMEDIATE is unnecessary for interpretive use, and we
> already have a nice word for "DUP >R @ + R> !".
> 
> Let's see how we can do a +TO-COMP
> 
> : +TO-COMP ( comp: "value" -- ; run-time: n -- )
>   ' >body postpone literal postpone +! ; immediate
> 
> We want the ' >BODY to happen at compile time, so we have to make
> +TO-COMP immediate, but the +! has to be at run-time, so we POSTPONE
> it to counter the IMMEDIATE.  And we have to get the address from
> compile-time to run-time; the POSTPONE LITERAL does that.
> 
> Now let's combine these two words into a word +TO; it's interpretation
> semantics should be +TO-INT, it's compilation semantics +TO-COMP:
> 
> ' +to-int ' +to-comp interpret/compile: +to
> 
> Tests:
> 5 value foo
> 6 +to-int foo
> foo .
> : bar +to-comp foo ;
> 7 bar
> foo .
> ' +to-int ' +to-comp interpret/compile: +to
> 8 +to foo
> foo .
> : boing +to foo ;
> 9 boing
> foo . 
> 
> - anton

This is total baloney! 

The ANS-Forth >BODY only works with words defined by CREATE. In 6.1.0550 it says: "An ambiguous condition exists if xt is not for a word defined via CREATE."

There is nothing in the ANS-Forth document (see 6.2.2405) that says VALUE is defined internally by CREATE DOES> --- this would only be true in crude compilers, but I would expect an optimizing compiler to define VALUE such that it generates a colon word. Local variables are not going to be defined with CREATE DOES> in any compiler, crude or optimizing.

Mark: Just use my +TO in my novice package --- that way you will have compatibility to any ANS-Forth compiler, and your +TO will work with both VALUEs and local variables.

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+TO in GForth Mark Wills <markrobertwills@yahoo.co.uk> - 2014-02-19 07:08 -0800
  Re: +TO in GForth Julian Fondren <julian.fondren@gmail.com> - 2014-02-19 07:31 -0800
  Re: +TO in GForth anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2014-02-19 15:36 +0000
    Re: +TO in GForth hughaguilar96@yahoo.com - 2014-02-20 21:36 -0800
      Re: +TO in GForth Harold <hzrabbie@gmail.com> - 2014-02-21 10:39 -0800
      Re: +TO in GForth Julian Fondren <julian.fondren@gmail.com> - 2014-02-23 04:31 -0800
        Re: +TO in GForth Mark Wills <markwills1970@gmail.com> - 2014-02-23 15:10 -0800
  Re: +TO in GForth hughaguilar96@yahoo.com - 2014-02-19 22:44 -0800

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