prolog - 如何将 if else 转换为 Prolog 中的完全声明式？

Question

这是我的类问题之一。

我能够使用一堆 if-else 创建自己的 Prolog 程序，但我被告知我的程序不是完全声明性的，因为它是 Prolog 的基本原则之一。

这是我的代码

%start with :- go.
is_spicy :-
  write('Do you want spicy? (yes/no)'),
  read(Preference),
  ( Preference == yes -> recommend("Curry"); recommend("Kurma") ).

is_fry :-
  write('Do you want fry food? (yes/no)'),
  read(Preference),
  ( Preference == yes -> recommend("StirFry"); recommend("Chicken") ).

is_chili :-
  write('Do you want chili? (yes/no)'),
  read(Preference),
  ( Preference == yes -> recommend("Sambal"); recommend("Singgang") ).

recommend(Food) :- write('We recommend you '), write(Food).

go :-
  write('Which food type do you prefer? (indian, chinese, malay): '),
  read(FoodType),
  (
    FoodType == indian -> is_spicy;
    FoodType == chinese -> is_fry;
    FoodType == malay -> is_chili;
    writeln('Please try again')
  ).

有人知道如何使其“完全声明式”吗？

Answer 1

如果解决代码中的冗余问题，从逻辑中提取数据，最终会得到更具声明性的代码。

因此，对数据结构进行编码，并提供一个能够提出问题并推断结果的“解释器”。

例如

dt(food_type,
    [indian  -> dt(spicy, [ y -> curry,   n -> curma ])
    ,chinese -> dt(fry,   [ y -> stirFry, n -> chicken ])
    ,malay   -> dt(chili, [ y -> sambal,  n -> singgang ])
    ]).

interpreter(dt(About, Choices), Choice) :-
   % present a menu for choices
   % recurse on selected path

% when it reach a leaf, just unify
interpreter(Choice, Choice).

您可能希望将菜单专门用于仅用于 y/n 的选择，但这取决于您

编辑

呈现菜单并接受选择需要额外的逻辑编程，例如:

solve(Choice) :-
    dt(About, Choices),
    interpreter(dt(About, Choices), Choice).

% present a menu for choices
% recurse on selected path
interpreter(dt(About, Choices), Choice) :-
  ask_user(About, Choices, ChoiceAbout),
  interpreter(ChoiceAbout, Choice).

% when it reach a leaf, just unify
interpreter(Choice, Choice).

ask_user(About, Choices, Choice) :-
  format('your choice about ~w ?~n', [About]), % show user the context of choice
  forall(member(C->_,Choices), format('   ~w~n', [C])),
  read(U),
  memberchk(U->Choice, Choices).

% note: if memberchk above fails (user doesn't input a correct choice)
% you should provide an alternate ask_user here, otherwise ...
% just see what the code does
%

示例 session :

% /home/carlo/Desktop/pl/choices compiled into choices 0.00 sec, 0 clauses

?- solve(C).

your choice about food_type ?
   indian
   chinese
   malay
|: chinese.

your choice about fry ?
   y
   n
|: n.

C = chicken .