[Vm-dev] Tangential: A Lisp Interpreter Implemented in Conway's Game of Life

Hernán Wilkinson hernan.wilkinson at 10pines.com
Sat Jan 21 20:06:05 UTC 2023

I see now how it works, thank you.


On Sat, Jan 21, 2023 at 5:48 AM Stéphane Rollandin <lecteur at zogotounga.net>

> > I can not map
> > that implementation to the rules of the game... Can someone explain to
> > me or point me to a paper/description of why that implementation works?
> There is the Byte paper, around
> https://archive.org/details/byte-magazine-1981-08/page/n205/mode/2up?view=theater
> The figure there shows how ancilliary forms are used to count, in
> parallel, the number of neighbors for each point in the pattern.
> For each direction in the Moore neighborood, the pattern is shifted and
> these eight shifted grids are combined together.
> This is an addition in base two, and we need to count up to eight, so
> the algorithm uses three forms (nbr1, nbr2 and nbr4) to store the
> corresponding bits, and two other forms (carry2 and carry4) to store the
> bits carried from one bit to the next (so here from nbr1 to nbr2, and
> from nbr2 to nbr4), just as you need to do when performing an addition
> by hand.
> The last step (the last four lines in #nextLifeGeneration from the Byte
> paper) generates the next pattern from nbr1, nbr2 and nbr4. The rules of
> the Game of Life are encoded here in the successive combination rules,
> in a nifty and quite obfuscated way that I did not even tried to
> comprehend.
> Stef


*Hernán WilkinsonAgile Software Development, Teaching & Coaching*
*Phone: +54-011*-4893-2057
*Twitter: @HernanWilkinson*
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