读取 prolog 中的输入并打印结果 [英] Read input in prolog and print result

问题描述

我正在学习 Prolog 的想法，这是我想要练习的内容:

I am learning Prolog ideas and here is what I want to practice:

我想写一个可以像这样工作的 Prolog 程序:

I want to write a Prolog program that can work like this:

?- input([apple,is,fruit]).
?- input([chicken,is,meat]).
?- input([Is,apple,meat]).
No, it is a fruit
?- input[(Is,chicken,meat])
Yes.

当我尝试实施这个程序时，我遇到了一些问题:

And when I was trying to implement this program, I got some problem:

(1) 我用这段代码试图读取输入并区分问题和断言，但失败了:

(1) I used this code trying to read the input and distinguish between questions and assertions, but it fails:

input([]).
input([X|R]) :- X is 'Is', write('test code read question'); write("test code read assertion").

(2) 我仍然对如何从输入消息中过滤有用信息感到困惑.例如，在 [Apple,is,fruit] 输入数组中，我只需要 apple 和 fruit.跳is字我们一般怎么做?

(2) I am still confused about How I can filter the useful information out from the input message. For example, in the [Apple,is,fruit]input array, all I need is apple and fruit. How do we normally do to jump the is word?

我不想给程序硬编码太多东西，更喜欢好的函数式编程风格来解决可以帮助我从中学习的问题.

I don't want to hardcode too many things to the program, and prefer a good functional programming style to solve the problem that can help me learn from it.

提前致谢.

推荐答案

仅仅因为我喜欢它们，我就倾向于使用定语从句语法 (DCG).然后你就可以很容易地做出语句并解析它们:

Just because I enjoy them, I'd be inclined towards a definite clause grammar (DCG). Then you can make statements and parse them fairly easily:

word(Word) --> [Word].
statement(Statement) --> 
    word(Thing), [is], word(Category), 
    { Statement =.. [Category, Thing] }.

这里使用 DCG 的技巧是您的语法正在转换为差异列表表示.括号内为普通Prolog代码；它周围的部分被解释为列表的文字部分或其他语法规则.所以 [Word] 匹配一个原子.我们实际上可以这样编写规则:

The trick going on here with DCGs is that your grammar is being transformed to a difference list representation. The part in brackets is normal Prolog code; the part around it is interpreted either as literal parts of the list or as other grammar rules. So [Word] is matching one atom. We could actually write the rule like this:

statement(Statement) -->
    [Thing, is, Category],
    { Statement =.. [Category, Thing] }.

它会产生相同的效果，而且可能更具可读性，但我喜欢迂腐.请特别注意 =.. 的使用，它将列表转换为事实，反之亦然(所以 [fruit, apple] 变成 fruit(apple)).

and it would have the same effect, and perhaps be more readable, but I like being pedantic. Note especially the use of =.., which converts lists into facts and vice versa (so [fruit, apple] becomes fruit(apple)).

使用 DCG 进行解析非常简单:使用 phrase/2:

Parsing with DCGs is quite easy: use phrase/2:

?- phrase(statement(X), [apple,is,fruit]).
X = fruit(apple).

然后你可以使用asserta将这些子句插入到动态存储中:

Then you can use asserta to insert these clauses into the dynamic store:

input(Text) :- 
    phrase(statement(Statement), Text),
    asserta(Statement).

例如:

?- input([apple,is,fruit]).
true.

?- fruit(X).
X = apple.

现在您可以编写另一个子句来解析查询:

Now you can write another clause for parsing queries:

query(Query) --> 
    ['Is'], word(Word), word(Category), 
    { Query =.. [Category, Word] }.

看起来非常相似！同样，如果您愿意，可以使用以下语法:

Looks very similar! And again, if you wanted, you could use this syntax:

query(Query) -->
    ['Is', Word, Category],
    { Query =.. [Category, Word] }.

现在您可能想编写一个子句，将两个语法规则组合成一个句子"规则:

Now you might want to write a clause to combine both grammar rules into one "sentence" rule:

sentence(statement(S)) --> statement(S).
sentence(query(Q))     --> query(Q).

试试看:

?- phrase(sentence(X), ['Is', apple, fruit]).
X = query(fruit(apple)).

?- phrase(sentence(X), [apple, 'is', fruit]).
X = statement(fruit(apple)) ;

您现在看到，我们不仅得到了解析的事实，而且还得到了一个包装器，它告诉我们它是语句还是查询.我们现在可以用这个代替语句和查询来解析，并像这样重写 input :

You see now we get not just the parsed fact, but also a wrapper that tells us whether it was a statement or a query. We can now parse with this instead of statement and query, and rewrite input like so:

input(Text) :-
    phrase(sentence(S), Text), perform(S).

我添加了一个辅助来处理工作:

I've added an auxiliary to handle the work:

perform(statement(S)) :- asserta(S).
perform(query(Q))     :- Q.

当您添加更多语法抽象时，这将在以后方便:每个 perform 子句处理不同的句子"类型，因此您进行上面的解析并处理下面的工作.现在我们或多或少有了你想要的:

This will be convenient later as you add more grammatical abstractions: each perform clause handles a different "sentence" type, so you do your parsing above and handle the work below. And now we have, more or less, what you wanted:

?- input([apple,is,fruit]).
true ;
false.

?- input(['Is',apple,fruit]).
true.

?- input(['Is',banana,fruit]).
false.

您可以通过在您的 sentence 规则中引入删减并使用特殊输出处理真/假来改进事情，但我认为这是我想要进入的方向，特别是如果您愿意以便将来能够处理不同的语法.

You can improve things by introducing a cut in your sentence rule and handling true/false with special output, but I think this is the direction I'd want to go in, particularly if you want to be able to handle different syntax in the future.

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