% nacteni:
/* ['7.1_11.pl']. */
% minimax( Pos, BestSucc, Val ):
% Pos is a position , Val is its minimax value ;
% best move from Pos leads to position BestSucc
minimax(Pos, BestSucc, Val) :-
moves(Pos, PosList), ! , % Legal moves in Pos produce PosList
best(PosList, BestSucc, Val)
;
staticval( Pos, Val ). % Pos has no successors : evaluate statically
best([Pos], Pos, Val) :-
minimax(Pos,_, Val), ! .
best([Pos1 | PosList], BestPos, BestVal) :-
minimax(Pos1,_, Val1),
best(PosList, Pos2, Val2),
betterof(Pos1, Val1, Pos2, Val2, BestPos, BestVal).
betterof(Pos0, Val0, _Pos1, Val1, Pos0, Val0) :- % Pos0 better than Pos1
min_to_move(Pos0), % MIN to move in Pos0
Val0 > Val1, ! % MAX prefers the greater value
;
max_to_move(Pos0), % MAX to move in Pos0
Val0 < Val1, ! . % MIN prefers the lesser value
betterof(_Pos0, _Val0, Pos1, Val1, Pos1, Val1). % Otherwise Pos1 better than Pos0