Newsgroups: comp.lang.forth
Subject: Re: Operator =?UTF-8?B?b3ZlcmxvYWRpbmc/?=
References: <a1aab44ee3b1b56c2f54f2606e98d040@www.novabbs.com> <2024Jul25.140858@mips.complang.tuwien.ac.at> <a0acecd6d9e2fd8067bf19c9050b1c15@www.novabbs.com> <2024Jul27.173555@mips.complang.tuwien.ac.at>
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In article <2024Jul27.173555@mips.complang.tuwien.ac.at>,
Anton Ertl <anton@mips.complang.tuwien.ac.at> wrote:
>minforth@gmx.net (minforth) writes:
>>On Thu, 25 Jul 2024 12:08:58 +0000, Anton Ertl wrote:
>>>>I am thinking on a much smaller scale i.e. unification of
>>>>operators for xVALUEs and xLOCALs. ANS Forth already has
>>>>overloaded TO but stops there.
>>>
>>> +TO is a common extension.
>>
>>Certainly. I have some array operations in mind, but they
>>are not relevant here. The principle is like
>>
>>: INIT { a }
>>  [[: a ;]] \ read counter
>>  [[: 1 +to a ;]] ; \ increment counter
>>DEFER count IS count
>>DEFER read IS read
>>5 INIT
>>COUNT COUNT READ -> should give 7
>
>My guess is that three lines here should be
>
>DEFER count
>DEFER read
>5 INIT IS count IS read
>
>>[[: ;]] define closures, but unlike gforth's more flexible
>>flat closures, they capture simply all upvalues (here local a).
>
>Gforth's flag closures can be considered lower-level (they come out of
>implementation ideas in the Scheme community) and are easier to
>implement, but emulating closures that capture outer locals is more
>cumbersome.  One other aspect is that in Gforth's closures the
>programmer decides whether closures are allocated in the dictionary,
>on the locals stack, on the heap, or elsewhere.  In the present case
>the dictionary seems to be a good place, and one can write this
>example as:
>
>: init ( a -- )
>  align here >r , \ allocate a on the heap
>  r@ [n:d @ ;]         \ read counter
>  r> [n:d 1 swap +! ;] \ increment counter
>;
>DEFER count
>DEFER read
>5 INIT IS count IS read
>count count read . \ prints "7 "
>
>INIT uses pure-stack closures [n:d consumes a value (in this exampl,
>the address of the cell containing A) from the stack at closure
>creation time and pushes it on the stack at closure run-time.  Look,
>Ma, no locals:-).
>
>However, this does not use value-flavoured stuff, because we have to
>pass the address of A around, and then it's easier to use the
>variable-flavoured words.  However, if you prefer the value-flavoured
>words, value-flavoured fields were recently added to Gforth and can be
>used to do that:
>
>begin-structure counter
>  value: counter-val
>end-structure
>: init ( a -- )
>  align here >r counter allot
>  r@ to counter-val
>  r@ [n:d counter-val ;]
>  r> [n:d 1 swap +to counter-val ;]
>;
>DEFER count
>DEFER read
>5 INIT IS count IS read
>count count read . \ prints "7 "
>
>However, you still have to deal with the address explicitly, which
>becomes especially obvious in the counter closure.
>
>This raises the question of why you want to use closures for this
>task.  Why not use one of the object-oriented Forth packages, some of
>which support value-flavoured fields (Mini-OOF2 among them AFAIK).
>
>>The code compiles unmodified for different types of a.
>>Incidentally, it compiles now with +TO, but realistically you
>>can't declare new 'op'TOs for too many different 'op' operators.
>
>This statement can be read in two different ways.  I think there can
>be too many, but Stephen Pelc may think otherwise:-).

Also Marcel Hendrix thinks that. I count a dozen opTO's in tforth
and iforth.
Personnaly I hate TO and +TO, but if you decide to use them, you
could as well go all the way.

>
>- anton

Groetjes Albert
-- 
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