Date: Sun, 15 Sep 2024 18:14:17 +1000
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Subject: Re: Avoid treating the stack as an array [Re: "Back & Forth" is
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On 15/09/2024 3:13 am, Ahmed wrote:
> On Sat, 14 Sep 2024 15:08:36 +0000, Anton Ertl wrote:
> 
>> I wonder if the notation "mf(x;a,b,c)" indicates that a,b,c is a tuble
>> that tends to get passed around without changing it.  In that case
>> defining it as a structure in memory and accessing its members there
>> might be a solution.
> 
> a, b and are the parameters of the membership function.
> Yes, we can use structures, arrays ...
> 
> 
>>
>> But OTOH, unless you see programming in Forth as a religious exercise,
>> why worry, as long as your solution works.
> 
> I did it without locals as an exercise. Here it is:
> 
> 
> Without locals:
> 
> : tri_mf: ( f: a b c )
>     create frot f, fswap f, f,
>     does>             ( ad_a)           ( f: x)
>       dup fdup        ( ad_a ad_a)      ( f: x x)
>       f@              ( ad_a)           ( f: x x a)
>       f>=             ( ad_a -1|0)      ( f: x)
>       over float+     ( ad_a -1|0 ad_b) ( f: x)
>       fdup f@         ( ad_a -1|0)      ( f: x x b)
>       f< and if       ( ad_a)           ( f: x)
>         dup f@ f-     ( ad_a)           ( f: x-a)
>         dup f@        ( ad_a)           ( f: x-a a)
>         float+        ( ad_b)           ( f: x-a a)
>         f@ fswap f-                     ( f: x-a b-a)
>         f/                              ( f: [x-a]/[b-a])
>         exit
>       then
>       float+          ( ad_b)           ( f: x)
>       dup fdup        ( ad_b ad_b)      ( f: x x)
>       f@              ( ad_b)           ( f: x x b)
>       f>=             ( ad_b -1|0)      ( f: x)
>       over float+     ( ad_b -1|0 ad_c) ( f: x)
>       fdup f@         ( ad_b -1|0)      ( f: x x c)
>       f< and if       ( ad_b)           ( f: x)
>         dup float+ f@ ( ad_b)           ( f: x c)
>         f-            ( ad_b)           ( f: x-c)
>         dup float+    ( ad_b ad_c)      ( f: x-c)
>         swap f@ f@ f-                   ( f: x-c b-c)
>         f/                              ( f: [x-c]/[b-c])
>         exit
>       then
>       drop fdrop
>       0e
> ;

That appears no better than FVALUEs ...

0e fvalue a
0e fvalue b
0e fvalue c
0e fvalue x

: tri_mf() ( f: x a b c -- mv)
  to c  to b  to a  to x
  x a f>=
  x b f< and if
    x a f- b a f- f/ exit
  then
  x b f>=
  x c f< and if
    c x f- c b f- f/ exit
  then
  0e
;