On Fri, Jan 5, 2018 at 5:42 PM, Hendrik Boom <hend...@topoi.pooq.com> wrote:

> Long ago in the 60's, on an old PDP-11 running an early Unix, I
> implemented a Live using quad-trees for storage after I noticed by
> drawing on a lengthy printout that at each level of the quadtree, only
> about half of the quads has objects in them.  The empty ones I could
> leave out  of storage and not do much computation with them (except at
> the edges in case they wee to come back to life).
> I could get simply *huge* Life patterns on this rather small machine (by
> today's standards) without running out of RAM.  I did have to rescale
> the screen display several times.  A pixel ended up meaning something
> like "there is something in this 8x8 block".
> Well, what had to be used as a pixel on an ascii-text-only terminal.

Must have been incredible at the time!
Can you tell how close to the 1980's HashLife algorithm [1] your
implementation was? It seems quite related at least. The first time I saw
these exponential speed ups, I was blown away. People seeing your
implementation likely felt similarly.

I would love to see a clean Scheme/Racket implementation of HashLife.

[1] https://en.wikipedia.org/wiki/Hashlife, impressively implemented in
Golly [2]
[2] http://golly.sourceforge.net/

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