Prolog唯一值检查错误

Question

我有4个人下订单，我希望他们每个人都吃不同的饮料和不同的甜点。但是uniq的饮料不起作用，我找不到原因？

person(X):- X=steve; X=sam; X=sue; X=sara.

desert(X):- X=fruit; X=pie; X=ice_cream; X=cake.

beverage(X):- X=water; X=coffee, X=milk; X=tea.

uniq(X,Y,Z,W):- dif(X,Y), dif(X,Z), dif(X,W), dif(Y,Z), dif(Y,W), dif(Z,W).

order_all(Person1,D1,B1,Person2,D2,B2,Person3,D3,B3,Person4,D4,B4):-    
   uniq(Person1,Person2,Person3,Person4) ,
   person(Person1),
   person(Person2),
   person(Person3),
   person(Person4),
   uniq(D1,D2,D3,D4),
   desert(D1),
   desert(D2),
   desert(D3),
   desert(D4).

order_b(B1,B2,B3,B4):-
   uniq(B1,B2,B3,B4),
   beverage(B1),
   beverage(B2),
   beverage(B3),
   beverage(B4).

Answer 1

你有一个错字：

beverage(X):- X=water; X=coffee, X=milk; X=tea.
                               ^
                           Right here

用分号代替冒号。