1
肯定是一個愚蠢的問題,但我不能自己回答。我有以下代碼:使用查詢結果進行計算
%% Ownedby-relationship in monopoly
ownedby(bank,weststation).
%% Account-Value:
account(player1,1500).
%% Prices
price(weststation,200).
%% Buy an estate in monopoly
buy(X,Y):-
ownedby(bank,X),
!,
retract(ownedby(bank, X)),
assert(ownedby(Y,X)),
price(X,Price),
account(Y,Accountold),
retract(account(Y,Accountold)),
assert(account(Y,Accountold-Price)).
%% Example:
buy(player1,weststation).
%% RESULT:
account(player1,X).
1500-200
所以串1500和200被連接起來,但沒有數字中減去... :(什麼原因德