Since we have complete the translation of Hunt the Wumpus to
Prolog, we might also report on how we did it. The game play
is basically a discovery of a tunnel system, whereby the discovery
only happens in the brain of the player. In larger editions of the
game the tunnel system is not fixed, but we went with a fixed version.
The only variable per game are the locations of the player, wumpus
holes and bats, and during the game the location of the player and the
wumpus. And there are also arrows. We found a BASIC source of the
game in an Atari archive about creative computing. We based our
translation to Prolog strictly on this 1972 source by Gregory Yob:
Original Hunt the Wumpus BASIC Program from 1972
https://www.atariarchives.org/bcc1/showpage.php?page=247
To realize the game we didn't use any assert and retract. We also didn't use
any repeat fail loops, except for asking the end user about some choice. This
was the prevalent pattern for user interaction. Here is an example from the
code wumpus.pl, asking whether the end-user wants to move or shoot:
choose(O) :- repeat,
write('SHOOT OR MOVE (S-M)? '), flush_output,
read_line(I),
( 'S' = I
-> O = 1
; 'M' = I
-> O = 2; fail), !.
On the otherhand the game play itself was coded Erlang Style.
The intial state was generate into a list. And the game state is just
passed along and modified along tail-recursive and mutally-recursive
predicate calls. This is already seen in the main loop:
% 0400 REM-MOVE OR SHOOT
% play(+List, +List, +Integer)
play(M, L, A) :-
location(L),
choose(O),
( O = 2
-> move(L, H),
check(H, R, F),
B = A
; rooms(N),
path(N, [], P),
shoot(P, L, A, R, B, F)),
result(F, M, R, B).
% result(+Integer, +List, +List, +Integer)
result(0, M, L, A) :- !,
play(M, L, A).
In the above play/3 calls result/4, and result/4 calls play/3. But the game
also contains many sub loops. Like bats might carry away the player
multiple times, or an arrow can be shot along a path with many steps.
Hunt the Wumpus as a Prolog Package at Jekejeke
https://github.com/jburse/jekejeke-samples/tree/master/pack/games
Hunt the Wumpus as a Prolog Package at SWI-Prolog
https://www.swi-prolog.org/pack/list?p=wumpus