如何在 Prolog 中请求用户选择？

Question

我刚开始学习 Prolog。我正在练习水果样本。但我无法创建允许用户按数字 select 的结构。我在网上看的例子，对水果样例无效

当我在SWISH-Prolog上运行下面的代码时，我要将列表中的值一一写上去。我怎样才能 select "1,2,3,4" 而不是红色、橙色、黄色、绿色、紫色、桃红色？

错误代码块：

menuask(Attr, Val, List) :- 
    write('What is the value for '), write(Attr), write('? '), nl,
    write (1. red), nl,
    write (2. orange), nl,
    read(Ans),
    check_val(Ans, Attr, Val, List),
    asserta(known(yes, Attr, Ans)),
    Ans == Val.

中的"menuask"报错。我试过了。

序言所有代码：

:- dynamic(known/3).
:- discontiguous menuask/3.
:- discontiguous ask/2.
% 
% % Data: fruit(X) :- attributes(Y)
fruit(banana) :- colour(yellow), shape(crescent).
fruit(apple) :- (colour(green); colour(red)), shape(sphere), stem(yes).
fruit(lemon) :- colour(yellow), (shape(sphere);shape('tapered sphere')), acidic(yes).
fruit(lime) :- colour(green), shape(sphere), acidic(yes).
fruit(pear) :- colour(green), shape('tapered sphere').
fruit(plum) :- colour(purple), shape(sphere), stone(yes).
fruit(grape) :- (colour(purple);colour(green)), shape(sphere).
fruit(orange) :- colour(orange), shape(sphere).
fruit(satsuma) :- colour(orange), shape('flat sphere').
fruit(peach) :- colour(peach).
fruit(rhubarb) :- (colour(red); colour(green)), shape(stick).
fruit(cherry) :- colour(red), shape(sphere), stem(yes), stone(yes).

% Expert recogniser
% Asks
colour(X) :- menuask(colour, X, [red, orange, yellow, green, purple, peach]).
shape(X) :- menuask(shape, X, [sphere, crescent, 'tapered sphere', 'flat sphere', stick]).
acidic(X) :- ask(acidic, X).
stem(X) :- ask(stem, X).
stone(X) :- ask(stone, X).

% Remember what I've been told is correct
ask(Attr, Val) :- known(yes, Attr, Val), !.
menuask(Attr, Val, _) :- known(yes, Attr, Val), !.
% % Remember what I've been told is wrong
ask(Attr, Val) :- known(_, Attr, Val), !, fail.
menuask(Attr, Val, _) :- known(_, Attr, Val), !, fail.
% Remember when I've been told an attribute has a different value
ask(Attr, Val) :- known(yes, Attr, V), V \== Val, !, fail.
menuask(Attr, Val, _) :- known(yes, Attr, V), V \== Val, !, fail.
% % I don't know this, better ask!
ask(Attr, Val) :- write(Attr:Val), write('? '), read(Ans), asserta(known(Ans, Attr, Val)), Ans == yes.
menuask(Attr, Val, List) :- 
    write('What is the value for '), write(Attr), write('? '), nl,
    write(List), nl,
    read(Ans),
    check_val(Ans, Attr, Val, List),
    asserta(known(yes, Attr, Ans)),
    Ans == Val.

check_val(Ans, _, _, List) :- member(Ans, List), !.
check_val(Ans, Attr, Val, List) :- 
    write(Ans), write(' is not a known answer, please try again.'), nl,
    menuask(Attr, Val, List).

go :- fruit(Fruit), write('The fruit is '), write(Fruit), nl.

Answer 1

我不是很清楚问题的重点，但也许这会有所帮助。下面是一个如何获取与输入的数字对应的名称的简单示例：

fruit(1, apple).
fruit(2, pear).
fruit(3, orange).

read_fruit(FruitName) :-
    repeat,
    write('Please select a fruit:'), nl,
    write_fruit_list,
    read(FruitNumber),
    (   fruit(FruitNumber, FruitName)
    ->  write('You selected: '), write(FruitName), nl, !
    ;   write('Not a valid choice, try again...'), nl, fail
    ).

write_fruit_list :-
    fruit(N, Name),
    write(N), write('. '), write(Name), nl,
    fail.
write_fruit_list.

这是您使用时的样子：

2 ?- read_fruit(F).
Please select a fruit:
1. apple
2. pear
3. orange
|: 4.
Not a valid choice, try again...
Please select a fruit:
1. apple
2. pear
3. orange
|: 3.
You selected: orange
F = orange.

3 ?-

如果你想让它不断地请求水果输入，你可以去掉切割。

如何在 Prolog 中请求用户选择？

How to ask for user choice in Prolog?

menu

prolog

user-input

choice

text-based