Prolog-关于事实的小练习 [英] Prolog - Little exercise on facts

问题描述

好的.那是我的问题.我需要实现一个谓词，该谓词汇总列表中产品的所有价格.但是，到目前为止，我对此没有任何进一步的了解. 我究竟做错了什么? 预先感谢.

Ok. That's my problem. I need to implement a predicate that sums up all the prices of the products in the list. But, for now, I'm not getting any further with it. What am I doing wrong? Thanks in advance.

domains
    state =  reduced ; normal

database
    producte (string, integer, state)
predicates
    nondeterm calculate(integer)

clauses 
   % ---> producte( description , price , state )
    producte("Enciam",2,normal). 
    producte("Llet",1,reduced). 
    producte("Formatge",5,normal). 
    calculate(Import):-
        producte(_,Import,_).
    calculate(Import):-
        producte(_,Import,_),
        calculate(Import2),
        Import=Import2+Import,!.

Goal
    calculate(I). 

推荐答案

免责声明:关于序言，我有点傻.另外，我现在无法访问序言解释器.

Disclaimer: I'm a bit daft when it comes to prolog. Also, I don't have access to a prolog interpreter right now.

典型示例，列表总和:

sum([], 0).
sum([Head | Tail], Total) :- sum(Tail, Temp), Total is Head + Temp.

使用findall/3列出列表:

making a list with findall/3:

findall(Val, producte(_, Val, _), Vals).

Vals有您想要汇总的列表.

Vals has your list you want to sum.

更新:根据您的评论，我有点无法联系翻译了.

Update: per your comment, I'm a bit out of my depth without access to an interpreter.

calculate(I) :- sum(Vals, I), findall(Val, producte(_, Val, _), Vals).

我认为这是做什么的

使用您的单个目标I，该目标接收由findall生成的Vals列表求和的结果.但是自从我使用序言以来已经有很长时间了，以至于我什至都没有正确的语法来做自己想做的事情.但是，只需进行少量改动就可以实现一个目标.

uses your single goal I, which receives the result of summing your Vals list, which is generated by findall. But it's been so long since I've used prolog that I may not even have the syntax right for doing what I want. However, a small variation should accomplish what you want with a single goal.

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