如何让程序继续下去？

Question

如何在menu1/0出现后让程序继续false

mylist([a,b,c]).
myprog(X) :- mylist(L), member(X, L).

go :- start_message,menu1.

start_message :- 
    write('This is a program.'),nl,
    write('Below are a list:'),nl,
    myprog(X), 
    write(X),nl, 
    fail.

menu1 :-
    nl,write('Select operation:'),nl,
    write('1. Input time'),nl,
    write('2. Exit program'),nl.

以下是我的观点：

go.
This is a program.
Below are a list:
a
b
c
false

Answer 1

你可以这样做

start_message :- 
    write('This is a program.'),nl,
    write('Below are a list:'),nl,
    ( myprog(X),
      write(X),nl, 
      fail
    ; true ).

现在myprog/1不能再成功，控制权转到true/0，start_message/0成功。

Answer 2

删除fail的最后一行中的start_message语句。