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eparadis/mandel.fth

Last active February 5, 2022 03:14
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classic terminal mandelbrot in FORTH
Raw
mandel.fth
\ from proposal http://www.forth200x.org/fvalue.html
variable %var
: to 1 %var ! ;
: fvalue create f, does> %var @ if f! else f@ then 0 %var ! ;
0e0 fvalue i3
0e0 fvalue r3
59 value x1
21 value y1
-1e0 fvalue i1
1e0 fvalue i2
-2e0 fvalue r1
1e0 fvalue r2
r2 r1 f- x1 s>f f/ fvalue s1 \ L30
i2 i1 f- y1 s>f f/ fvalue s2 \ L31
: single_iter { F: z1 F: z2 } ( F: z1 F: z2 -- F: z1' F: z2' F: mag )
z1 fdup f* fdup \ L90 ( -- a a )
z2 fdup f* fdup \ L91 ( -- a a b b )
frot \ ( -- a b b a )
f+ \ ( -- a b mag ) L100
frot frot \ ( -- mag a b )
f- r3 f+ \ z1 \ L111 ( -- mag z1' )
2e0 z1 z2 f* f* i3 f+ \ z2 L110 ( -- mag z1' z2' )
frot \ ( -- z1' z2' mag )
;
: print_char ( F: x F: y -- )
62 \ character to emit w/ a single iteration
30 \ push the max in case we don't exit early
30 0 do \ L80
single_iter
4e0 f> if
drop i \ replace the max with the actual number of times we iterated
leave
then
loop \ L120
fdrop fdrop \ clean z1 and z2 left from single_iter
- emit \ L130
;
: calc_i3 { y }
y s>f s2 f* i1 f+ to i3 \ L50
;
: calc_r3 { x }
x s>f s1 f* r1 f+ to r3 \ L70
;
: mandel
cr \ always start on a fresh clean line
y1 0 do \ L40
i calc_i3
x1 0 do \ L60
i calc_r3
r3 i3 print_char
loop \ L140
cr \ L150
loop \ L160
;
mandel
bye
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eparadis commented Feb 5, 2022

Unpacking the "polyfill" fvalue at the top:

variable %var \ make a variable named "%var"
: to 1 %var ! ; \ make a word "to" that stores decimal 1 into %var
: fvalue
  create   \ make a new dictionary entry. Its name is the next word in the parse stream. It puts the address of its body on the data stack when executed
  f,       \ allocate dictionary space for a floating point number in the body of the new dictionary entry
  does>    \ set what the body of the dictionary word created just now to:
    %var @ \ push the value of %var on to the stack
    if     \ if the top of the stack is true (non-zero) ...
      f!   \ ... store the top of the floating point stack into the address at the top of the data stack (ie: the address of the space reserved in the body of the new dictionary word)
    else   \ otherwise, when the TOS was false (non-zero )...
      f@   \ ... fetch the value of the floating point number at the address on the top of the data stack (ie: what was stored in the body above)
    then   \ afterwards,
    0 %var ! \ store zero into %var
;

So there is one use of fvalue:

1e0 fvalue foobar
Create a new word named foobar and store 1.0 into its dictionary entry, along with setting the run-time behavior of foobar

You can then use that word two ways:

foobar \ Put the value of foobar onto the (floating point) stack
The default operation of foobar just pushes a copy of the value stored inside it's dictionary entry.

3e0 to foobar \ Set foobar to the new value of 3.0.
to puts foobar into "storing mode", which sets the value held in it's dictionary entry.

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