farmer.pl
Version 1
Based on this version from UCSD.
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%% Travel E -> W travel(e,w). %% Travel W -> E travel(w,e). %% Possible moves. move([X,X,Goat,Cabbage],wolf,[Y,Y,Goat,Cabbage]) :- travel(X,Y). move([X,Wolf,X,Cabbage],goat,[Y,Wolf,Y,Cabbage]) :- travel(X,Y). move([X,Wolf,Goat,X],cabbage,[Y,Wolf,Goat,Y]) :- travel(X,Y). move([X,Wolf,Goat,Cabbage],nothing,[Y,Wolf,Goat,Cabbage]) :- travel(X,Y). %% Safe conditions. safe([X,_,X,_]). % Goat is on the same bank as farmer. safe([X,X,_,X]). % Wolf and cabbage are on the same bank as farmer solve([e,e,e,e],[]). solve(State,[FirstMove|OtherMoves]) :- move(State, FirstMove, NextState), safe(NextState), solve(NextState, OtherMoves). % ?- length(X,7), solve([w,w,w,w],X). % X = [goat, nothing, wolf, goat, cabbage, nothing, goat] ; % X = [goat, nothing, wolf, goat, cabbage, nothing, goat] ; % X = [goat, nothing, cabbage, goat, wolf, nothing, goat] ; % X = [goat, nothing, cabbage, goat, wolf, nothing, goat] ; % false. % ?- length(X,7), setof(t,solve([w,w,w,w],X),_). % X = [goat, nothing, cabbage, goat, wolf, nothing, goat] ; % X = [goat, nothing, wolf, goat, cabbage, nothing, goat]. |
Version 2 Additions
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not_member(_, []) :- !. not_member(X, [Head|Tail]) :- X \= Head, not_member(X, Tail). solve2(AnsPath) :- solve2([[w,w,w,w]], AnsPath). solve2([S|_], [S]) :- S = [e,e,e,e], !. solve2([S|Path], [S|AnsPath]) :- move(S, _, NextState), safe(NextState), not_member(NextState,[S|Path]), solve2([NextState, S | Path], AnsPath). % ?- solve2(X). % X = [[w, w, w, w], [e, w, e, w], [w, w, e, w], [e, e, e, w], [w, e, w, w], [e, e, w, e], [w, e, w, e], [e, e, e, e]] ; % X = [[w, w, w, w], [e, w, e, w], [w, w, e, w], [e, e, e, w], [w, e, w, w], [e, e, w, e], [w, e, w, e], [e, e, e, e]] ; % X = [[w, w, w, w], [e, w, e, w], [w, w, e, w], [e, w, e, e], [w, w, w, e], [e, e, w, e], [w, e, w, e], [e, e, e, e]] ; % X = [[w, w, w, w], [e, w, e, w], [w, w, e, w], [e, w, e, e], [w, w, w, e], [e, e, w, e], [w, e, w, e], [e, e, e, e]] ; |