如何获取Prolog的往返旅行结果？

Question

我有这个Prolog问题，我想检查三件事。

1. 可以从a到b，也可以从b到a
2. 可以从a到b，也可以从b到a，它告诉我从a到b的路线。
3. 与路线上的每一次旅行使用何种运输方式有关的第2号和补充信息相同。

目前，我设法得到了这个程序的第(1)部分，但当我运行，程序出来‘是’，即使它是一个错误的路线。不知道为什么。

byCar(auckland,hamilton).
byCar(hamilton,raglan).
byCar(valmont,saarbruecken).
byCar(valmont,metz).

byTrain(metz,frankfurt).
byTrain(saarbruecken,frankfurt).
byTrain(metz,paris).
byTrain(saarbruecken,paris).

byPlane(frankfurt,bangkok).
byPlane(frankfurt,singapore).
byPlane(paris,losAngeles).
byPlane(bangkok,auckland).
byPlane(losAngeles,auckland).

(1)

connect(X,Y):-byCar(X,Y);byCar(Y,X).
connect(X,Y):-byTrain(X,Y);byTrain(Y,X).
connect(X,Y):-byPlane(X,Y);byPlane(Y,X).

travel(X,Y):-travelLoop(X,Y,[]).
travelLoop(X,Y,_):-connect(X,Y).
travelLoop(X,Y,Passed):-connect(X,Thru),
    \+memberchk(Thru,Passed),
    travelLoop(Thru,Y,[Thru|Passed]),X\=Y.
travel(_,_):-write('Wrong travel input, please try again.'),nl.

(2)

travel(X,Y,go(X,Y)):-byCar(X,Y).
travel(X,Y,go(X,Y)):-byTrain(X,Y).
travel(X,Y,go(X,Y)):-byPlane(X,Y).
travel(X,Y,go(X,Z,W)):-travel(X,Z,go(X,Z)),travel(Z,Y,W).

(3)

travel1(X,Y,go(X,Y,car)):-byCar(X,Y).
travel1(X,Y,go(X,Y,train)):-byTrain(X,Y).
travel1(X,Y,go(X,Y,plane)):-byPlane(X,Y).
travel1(X,Y,go(X,Z,V,W)):-travel1(X,Z,go(X,Z,V)),travel1(Z,Y,W).

P.S. (2)和(3)不能想到来回谓词，只能得到一个方法。请帮帮忙。非常感谢。

Answer 1

首先，您的connect谓词忘记了传输模式。改为：

connect(X,Y,byCar):-   byCar(X,Y)   ; byCar(Y,X).
connect(X,Y,byTrain):- byTrain(X,Y) ; byTrain(Y,X).
connect(X,Y,byPlane):- byPlane(X,Y) ; byPlane(Y,X).

其次，在使用travelLoop的path参数时存在不一致之处：

travel(X,Y):-travelLoop(X,Y,[]).            %// -- start empty. Why not [X]?
travelLoop(X,Y,_):-connect(X,Y).            %// (1)
travelLoop(X,Y,Passed):-connect(X,Thru),
    \+memberchk(Thru,Passed),
    travelLoop(Thru,Y,[Thru|Passed]),       %// -- start from [Thru|...].
    X\=Y.                                   %// why here? should be at (1)

只有当第一个子句不成功时，travel的第二个子句才需要触发。为什么它是分离的？这两个子句在文件中应该是一个相邻的。

travel(_,_):-write('Wrong travel input, please try again.'),nl.
%// This says: succeed always, and tell the user it didn't. 
%// Need to join both clauses into one IF: (success -> true; wrong).

travelLoop的success子句缺失了：

travelLoop(X,Y, Path):- X=Y, %// report the Path to user: ... 
                        writeln( ... ).

至于返航，不是很简单吗？因此，将travelLoop重命名为travel_path，并将travel重写为

travel(X,Y):-   %// the to and fro loop
  travel_path(X,Y,[X]), travel_path(Y,X,[Y]) -> true ; wrong.

wrong:- writeln("Wrong input. Try again."), nl.

Answer 2

实际上，下面是我的程序的一部分，我们需要写一个菜单形式，所以这是菜单的一部分。我插入了你为我修正的内容，我尝试过，因为我认为它是有效的，因为我认为选择的任何两个目的地都会有“是”的答案，因为有一个来回循环。但是，我认为这会影响(c)和(d)项。所以我不知道矛盾在哪里。

choice(3):- write('Select the way: '),nl,nl,
  write('a. Travel by using the same transportation.'),nl,
  write('b. Travel by chaining together car, train, and plane journeys.'),nl,
  write('c. How to travel from one place to another: cities.'),nl,
  write('d. How to travel from one place to another: cities and transportation.'),nl,
  read(Option),nl,nl,
  write('Enter the place start from: '),read(Start),
  write('Enter the place end at: '),read(End),
  option(Option,Start,End),nl,nl.

option(a,A,B):- travelSimple(A,B),nl,write('yes'),nl,nl,menu. 
option(b,A,B):- travel(A,B),nl,write('yes'),nl,nl,menu.
option(c,A,B):- findall(X,travel(A,B,X),List),nl,writelist(List),nl,nl,menu.    
option(d,A,B):- findall(Y,travel1(A,B,Y),List1),nl,writelist(List1),nl,nl,menu.
option(_,_,_):- write('Wrong option input, please try again.'),nl,nl,menu.

travel1(X,Y):-byCar(X,Y).
travel1(Y,X):-byCar(X,Y).
travel2(P,Q):-byTrain(P,Q).
travel2(Q,P):-byTrain(P,Q).
travel3(M,N):-byPlane(M,N).
travel3(N,M):-byPlane(M,N).

travelSimple(X,Y):-byCar(X,Z),travel1(Z,Y);byCar(X,Y).
travelSimple(Y,X):-byCar(X,Z),travel1(Z,Y);byCar(X,Y).
travelSimple(P,Q):-byTrain(P,R),travel2(R,Q);byTrain(P,Q).
travelSimple(Q,P):-byTrain(P,R),travel2(R,Q);byTrain(P,Q).
travelSimple(M,N):-byPlane(M,L),travel3(L,N);byPlane(M,N).
travelSimple(N,M):-byPlane(M,L),travel3(L,N);byPlane(M,N).
travelSimple(_,_):-write('Wrong travel simple input, please try again.'),nl.

connect(X,Y,byCar):-   byCar(X,Y)   ; byCar(Y,X).
connect(X,Y,byTrain):- byTrain(X,Y) ; byTrain(Y,X).
connect(X,Y,byPlane):- byPlane(X,Y) ; byPlane(Y,X).

travel(X,Y):-travelLoop(X,Y,[X]).          
travelLoop(X,Y,_):- connect(X,Y,byCar);
                    connect(X,Y,byTrain);
                    connect(X,Y,byPlane), X\=Y.           
travelLoop(X,Y,Passed):-connect(X,Thru,byCar);
                    connect(X,Thru,byTrain);
                    connect(X,Thru,byPlane);
                    \+memberchk(Thru,Passed),travelLoop([Thru|Passed],Y,Thru). 
travelLoop(X,Y,Path):- X=Y, writeln('Yes')-> true ; wrong.      
travel(X,Y):-travel_Path(X,Y,[X]), 
     travel_Path(Y,X,[Y]) -> true ; wrong. 
wrong:- writeln('Wrong travel input, please try again.'), nl.

travel(X,Y,go(X,Y)):-byCar(X,Y).
travel(X,Y,go(X,Y)):-byTrain(X,Y).
travel(X,Y,go(X,Y)):-byPlane(X,Y).
travel(X,Y,go(X,Z,W)):-travel(X,Z,go(X,Z)),travel(Z,Y,W).
travel1(X,Y,go(X,Y,car)):-byCar(X,Y).
travel1(X,Y,go(X,Y,train)):-byTrain(X,Y).
travel1(X,Y,go(X,Y,plane)):-byPlane(X,Y).
travel1(X,Y,go(X,Z,V,W)):-travel1(X,Z,go(X,Z,V)),travel1(Z,Y,W).

writelist([]).
writelist([L|Lt]):-write(L),nl,writelist(Lt).