我正在Prolog中开发一个程序，就像一个快餐店的培训视频。我的代码可以编译，但是无论我回答什么，一旦进入第二种状态，我都会看到一条错误消息
“未捕获的异常：错误（existence_error（procedure，a / 0），top_level / 0）”
%Taylor Loslo
%Program 15
%Krusty Krab Training PRogram
start_state(uniformshirt).
next_state(uniformshirt,a,uniformshoes).
next_state(uniformshirt,b,uniformshoes).
next_state(uniformshoes,a,makekrabbypattystart).
next_state(uniformshoes,b,makekrabbypattystart).
next_state(uniformshoes,c,makekrabbypattystart).
next_state(uniformshoes,d,makekrabbypattystart).
next_state(makekrabbypattystart,a,cookedpattysv).
next_state(makekrabbypattystart,b,veggiesadded).
next_state(makekrabbypattystart,c,sauceadded).
next_state(makekrabbypattystart,d,makekrabbypattystart).
next_state(cookedpattysv,a,pattyveggies).
next_state(cookedpattysv,b,pattysauce).
next_state(veggiesadded,a,pattyveggies).
next_state(veggiesadded,b,veggiesauce).
next_state(sauceadded,a,pattysauce).
next_state(sauceadded,b,veggiesauce).
next_state(pattysauce,s,pattyfinished).
next_state(pattysauce,b,pattyfinished).
next_state(veggiesauce,s,pattyfinished).
next_state(veggiesauce,b,pattyfinished).
next_state(pattyveggies,s,pattyfinished).
next_state(pattyveggies,b,pattyfinished).
next_state(pattyfinished,s,pattyserved).
display_intro :-
write('WELCOME TO THE KRUSTY KRAB TRAINING PROGRAM'),nl,
write('Congratulations on your new job as FRY COOK '),nl,nl,
write('Lets get started!'),nl.
initialize :-
asserta(stored_answer(money,0)),
asserta(stored_answer(toes,10)),
asserta(stored_answer(handswashed,no)),
asserta(stored_answer(patty,no)),
asserta(stored_answer(veggies,no)),
asserta(stored_answer(secretsauce,no)).
goodbye :-
write('Training Results:'),nl,
write('Money: $'),stored_answer(money,_),nl,
write('Toes: '),stored_answer(toes,_),nl,nl.
show_state(uniformshirt) :-
write('You are deciding what to wear for your first day of work.'),nl,
write('Do you...'),nl,
write('(a) Wear your clean Krusty Krab polo shirt'),nl,
write('(b) Wear your favorite t-shirt that youve been wearing for 3 days straight'),nl,
write('(q) Quit'),nl,nl.
show_state(uniformshoes) :-
write('Before heading to work you have to put on shoes'),nl,
write('Do you pick...'),nl,
write('(a) Comfortable skater shoes'),nl,
write('(b) Non-slip sneakers'),nl,
write('(c) Flip flops'),nl,
write('(q) Quit'),nl,nl.
show_state(makekrabbypattystart) :-
write('Now that you are properly dressed lets make a Krabby Patty'),nl,nl,
write('Do you want to...'),nl,
write('(a) Start cooking the patty'),nl,
write('(b) Chop the veggies'),nl,
write('(c) Add secret sauce'),nl,
write('(d) Wash your hands'),nl,
write('(q) Quit'),nl,nl.
show_state(cookedpattysv) :-
write('Next do you want to...'),nl,
write('(a) Chop the veggies'),nl,
write('(b) Add secret sauce'),nl,
write('(q) Quit'),nl,nl.
show_state(pattysauce) :-
write('Next do you want to...'),nl,
write('(s) Serve it to the customer'),nl,
write('(b) Chop the Veggies'),nl,
write('(q) Quit'),nl,nl.
show_state(pattyveggies) :-
write('Next do you want to...'),nl,
write('(s) Serve it to the customer'),nl,
write('(b) Add the secret sauce'),nl,
write('(q) Quit'),nl,nl.
show_state(veggiesadded) :-
write('Next do you want to...'),nl,
write('(a) Cook the patty'),nl,
write('(b) Add secret sauce'),nl,
write('(q) Quit'),nl,nl.
show_state(veggiesauce) :-
write('(s) Serve it to the customer'),nl,
write('(b) Cook the patty'),nl,
write('(q) Quit'),nl,nl.
show_state(sauceadded) :-
write('Next do you want to...'),nl,
write('(a) Cook the patty'),nl,
write('(b) Chop the veggies'),nl,
write('(q) Quit'),nl,nl.
show_state(pattyfinished) :-
write('Next do you want to...'),nl,
write('(s) Serve it to the customer'),nl,
write('(q) Quit'),nl,nl.
show_state(pattyserved) :-
stored_answer(patty,yes),
stored_answer(veggies,yes),
stored_answer(secretsauce,no),
write('You forgot to add the secretsauce!'),nl,
write('The customer complains its dry and you have to make another'),nl,nl,
show_state(washedhands),
goodbye.
show_state(pattyserved) :-
stored_answer(patty,yes),
stored_answer(veggies,yes),
stored_answer(secretsauce,yes),
write('You served a perfect Krabby Patty!'),nl,nl,
show_state(washedhands),
goodbye.
show_state(pattyserved) :-
stored_answer(patty,no),
stored_answer(veggies,yes),
stored_answer(secretsauce,yes),
write('You forgot to add the patty!'),nl,
write('The customer complains and you have to make another'),nl,nl,
show_state(washedhands),
goodbye.
show_state(pattyserved) :-
stored_answer(patty,yes),
stored_answer(veggies,no),
stored_answer(secretsauce,yes),
write('You forgot to add the veggies!'),nl,
write('The customer does no complain because he always picks those off anyways'),nl,nl,
show_state(washedhands),
goodbye.
show_state(washedhands) :-
stored_answer(handswashed,yes),
write('Thank you for remembering to wash your hands before you started'),nl,nl.
show_state(washedhands) :-
stored_answer(handswashed,no),
write('You did not wash your hands before cooking the patty'),nl,
write('The customer gets sick and sues you.'),nl,nl,
stored_answer(money,Amount),
retract(stored_answer(money,_)),
Newamount is Amount - 10000,
asserta(stored_answer(money,Newamount)).
show_transition(uniformshirt,b) :-
write('Mr Krabs notices how filthy your shirt is and sends you home to put on a clean one'),nl,
write('You lost $5 in wages from missing work'),nl,nl,
stored_answer(money,Amount),
retract(stored_answer(money,_)),
Newamount is Amount - 5,
asserta(stored_answer(money,Newamount)).
show_transition(uniformshirt,a) :-
write('Looking good!'),nl,nl.
show_transition(uniformshoes,a) :-
write('You come into work and immediately slip on grease.'),nl,
write('You crack your skull open and have to miss work for 6 weeks'),nl,
write('Mr Krabs refuses to pay you workmans compensation'),nl,
write('Next time you come into work you wear non-slip shoes...'),nl,nl.
show_transition(uniformshoes,c) :-
write('OUCH!'),nl,
write('You lose your big toe when you drop a knife while you are cutting onions'),nl,
write('You come into work the next day with crutches and non-slip shoes...'),nl,nl,
stored_answer(toes,_),
retract(stored_answer(toes,_)),
asserta(stored_answer(toes,9)).
show_transition(uniformshoes,b) :-
write('Perfect! Those are the most practical shoes for the job'),nl,nl.
show_transition(sauceadded,a) :-
retract(stored_answer(patty,no)),
asserta(stored_answer(patty,yes)),
write('You cook the patty to perfection.'),nl,nl.
show_transition(sauceadded,b) :-
retract(stored_answer(veggies,no)),
asserta(stored_answer(veggies,yes)),
write('You chopped the onions, lettuce, and tomato. '),nl,
write('You added the veggies to the burger. '),nl,nl.
show_transition(makekrabbypattystart,a) :-
retract(stored_answer(patty,no)),
asserta(stored_answer(patty,yes)),
write('You cook the patty to perfection.'),nl,nl.
show_transition(makekrabbypattystart,d) :-
retract(stored_answer(handswashed,no)),
asserta(stored_answer(handswashed,yes)),
write('You washed your hands.'),nl,nl.
show_transition(pattysauce,b) :-
retract(stored_answer(veggies,no)),
asserta(stored_answer(veggies,yes)),
write('You chopped the onions, lettuce, and tomato. '),nl,
write('You added the veggies to the burger. '),nl,nl.
show_transition(veggiesauce,b) :-
retract(stored_answer(patty,no)),
asserta(stored_answer(patty,yes)),
write('You cook the patty to perfection.'),nl,nl.
show_transition(makekrabbypattystart,c) :-
retract(stored_answer(secretsauce,no)),
asserta(stored_answer(secretsauce,yes)),
write('You added the secret sauce to the burger. '),nl,nl.
show_transition(veggiesadded,b) :-
retract(stored_answer(secretsauce,no)),
asserta(stored_answer(secretsauce,yes)),
write('You added the secret sauce to the burger. '),nl,nl.
show_transition(veggiesadded,a) :-
retract(stored_answer(patty,no)),
asserta(stored_answer(patty,yes)),
write('You cook the patty to perfection.'),nl,nl.
show_transition(pattyveggies,b) :-
retract(stored_answer(secretsauce,no)),
asserta(stored_answer(secretsauce,yes)),
write('You added the secret sauce to the burger. '),nl,nl.
show_transition(makekrabbypattystart,b) :-
retract(stored_answer(veggies,no)),
asserta(stored_answer(veggies,yes)),
write('You chopped the onions, lettuce, and tomato. '),nl,
write('You added the veggies to the burger. '),nl,nl.
show_transition(cookpattysv,b) :-
retract(stored_answer(secretsauce,no)),
asserta(stored_answer(secretsauce,yes)),
write('You added the secret sauce to the burger. '),nl,nl.
show_transition(cookpattysv,a) :-
retract(stored_answer(veggies,no)),
asserta(stored_answer(veggies,yes)),
write('You chopped the onions, lettuce, and tomato. '),nl,
write('You added the veggies to the burger. '),nl,nl.
show_transition(_,s) :-
show_state(pattyserved).
go :-
intro,
start_state(X),
show_state(X),
get_choice(X,Y),
go_to_next_state(X,Y).
intro :-
display_intro,
clear_stored_answers,
initialize.
go_to_next_state(_,q) :-
goodbye,!.
go_to_next_state(S1,Cin) :-
next_state(S1,Cin,S2),
show_transition(S1,Cin),
show_state(S2),
stored_answer(moves,K),
OneMoreMove is K + 1,
retract(stored_answer(moves,_)),
asserta(stored_answer(moves,OneMoreMove)),
get_choice(S2,Cnew),
go_to_next_state(S2,Cnew).
go_to_next_state(S1,Cin) :-
\+ next_state(S1,Cin,_),
show_transition(S1,fail),
get_choice(S1,Cnew),
go_to_next_state(S1,Cnew).
get_choice(_,C) :-
write('Next entry (letter followed by a period)? '),
read(C).
% case knowledge base - user responses
:- dynamic(stored_answer/2).
% procedure to get rid of previous responses
% without abolishing the dynamic declaration
clear_stored_answers :- retract(stored_answer(_,_)),fail.
clear_stored_answers.
我完全被卡住了，如何丢失此错误并继续执行程序的其余部分？
答案 0 :(得分：0)
我添加了许多trace/1调用来弄清楚您的问题是什么，但是您可以通过执行trace(stored_answer/2)来找到它，因为您会看到以下内容：
Before heading to work you have to put on shoes
Do you pick...
(a) Comfortable skater shoes
(b) Non-slip sneakers
(c) Flip flops
(q) Quit
T Exit: (10) show_state(uniformshoes)
T Call: (10) stored_answer(moves, _5580)
T Fail: (10) stored_answer(moves, _5580)
T Redo: (10) show_transition(uniformshirt, a)
T Fail: (10) show_transition(uniformshirt, a)
T Redo: (9) go_to_next_state(uniformshirt, a)
T Call: (10) next_state(uniformshirt, a, _5582)
T Exit: (10) next_state(uniformshirt, a, uniformshoes)
T Fail: (9) go_to_next_state(uniformshirt, a)
false.
这表明stored_answer(moves, K)在循环的第一次迭代中失败，因为尚未初始化。因此，解决方案就是在您的initialize谓词上添加一行初始化该变量的行：
initialize :-
asserta(stored_answer(money,0)),
asserta(stored_answer(toes,10)),
asserta(stored_answer(handswashed,no)),
asserta(stored_answer(patty,no)),
asserta(stored_answer(veggies,no)),
asserta(stored_answer(secretsauce,no)),
asserta(stored_answer(moves,0)). %% <-- new
更改之后，该程序似乎可以按预期运行。