note that this isn't guaranteed, if the chain is such that the
current tuple has nowhere to go but to the end of the line, then
it will follow it --- it doesn't try to go back and rebuilt a different
chain or anything.
yeah, we have MegaHAL, but i can't find a good implementation in
python that actually works and is stable, so we'll implement a
simple thing ourselves. works pretty much like MegaHAL does, but
without the string corruption.
original code provided by ape, care of mike bloy