On
rec.games.roguelike.nethack, there was once a discussion on
whether it is possible for a
Nethack character to survive for an
infinitely long time. This does not refer to
ascension or to
explore mode or
wizard mode, but to a normal game lasting for
infinitely many turns. There are two factors one must control to
achieve this:
hit points and
nutrition. If either falls too low,
you die.
The method rgrn chose for keeping your hit points up was to make
sure that nothing could ever attack you. Surround yourself with a
wall of immobile monsters such as blue jellies to prevent monsters
from getting next to you. Then read a scroll of earth to create a
wall of boulders on top of the jellies, so that nothing will see you
and attempt a ranged attack. You may need to repeat this
procedure if some of the jellies don't survive the first time. It may
also be necessary to genocide mind flayers and master mind flayers,
because of their blasts of psychic energy.
Theoretically it would also be possible to kill so many monsters that
all types of monster become extinct - this practice is known as
extinctionist play. Extinction doesn't apply to quest levels, I
think, but you wouldn't have to stay there. The reason for going to
all this trouble to keep your HP from dropping is that, no matter how
fast your character heals, it would be impossible to prove that
they could kill anything the game threw at them.
Moving on to nutrition, you must either take a form that does not
need to eat, or ensure yourself an infinite supply of food. Relying
on prayer won't do, because the upper limit to prayer timeout is
very large. The poster on rgrn chose to polymorph into a xorn and
eat amulets of unchanging until he gained the unchanging intrinsic.
(Wearing the amulet won't do, as amulets cause food consumption.)
Ensuring an infinite supply of food is trickier but workable. Once
you've been everywhere in the dungeon and rendered every species of
monster extinct (which takes a very long, but finite, time), nothing
more will be generated. The exception for quest levels still
applies, but as before, we can't prove that you'd get enough food to
survive there, or that you wouldn't run out of hit points. So what
you need is a horn of plenty and the Platinum Yendorian Express
Card (to recharge the horn). This is not guaranteed to keep you
alive forever - perhaps the horn generates nothing but potions of
acid for a very long time. When you use this strategy, the total
amount of nutrition available to you, including a stockpile of food
you can't eat yet because you are satiated, goes up and down in an
unbounded random walk. Your probability of surviving forever is not
unity, but since the gain when you get a food ration is much greater
than the loss when you get a potion of acid, it is very high.