跨多个模块定义谓词的部分 [英] Define parts of a predicate across several modules

问题描述

我正在尝试编写一个谓词 move/3 来处理多种术语，每种术语都在一个单独的文件中定义.我正在尝试为此使用模块，因为文件包含其他应适当命名空间的谓词.

I'm trying to write a predicate move/3 which handles several kinds of terms, each kind of which is defined in a separate file. I'm trying to use modules for this, because the files contain other predicates which should be namespaced appropriately.

所以，我创建了一个包含内容的模块 cat.prolog:

So, I've created a module cat.prolog with contents:

:- module(cat, [move/3]).
:- multifile(move/3).

move(cat(C), P, cat(C2)) :-
   ...

dog.prolog 类似.

和 main.prolog 与:

:- use_module(['cat.prolog'], [move/3]).
:- use_module(['dog.prolog'], [move/3]).

(various predicates that use move/3 and expecting the clauses from all imported modules to be applicable.)

尝试在 SWI-Prolog 中运行:

Trying to run this in SWI-Prolog:

?- ['main.prolog'].
%  cat.prolog compiled into cat 0.00 sec, 4,800 bytes
ERROR: Cannot import dog:move/3 into module user: already imported from cat
Warning: /home/edmund/main.prolog:2:
        Goal (directive) failed: user:use_module([dog.prolog],[move/3])
% main.prolog compiled 0.00 sec, 10,176 bytes
true.

此时我可以使用 dog:move/3 和 cat:move/3 但不能使用 move/3.它适用于 cat 情况，但不适用于 dog 情况.

At this point I can use dog:move/3 and cat:move/3 but not move/3. It works for the cat case but not the dog case.

我觉得有一种非常明显的方法可以做到这一点.我已经尝试以多种方式组合模块和导入以及多文件指令，但仍然没有找到它......

I get the feeling there's a really obvious way to do this. I've tried combining modules and imports and multifile directives in many ways and still not found it yet...

推荐答案

multifile/1 语法很简单，但是 文档 缺少一个简单的例子...

The multifile/1 syntax is simple, but the documentation lacks a simple example...

我创建了 3 个 modules 文件:pets.pl、cat.pl、dog.pl.

I created 3 modules files: pets.pl, cat.pl, dog.pl.

:- module(pets, [test/0, move/3]).
:- multifile move/3.
move(A,B,C) :- writeln(pets-move(A,B,C)).
test :- forall(move(A,B,C), writeln(move(A,B,C))).

:- module(cat, []).
:- use_module(pets).
pets:move(A,B,C) :- writeln(cat-move(A,B,C)).

:- module(dog, []).
:- use_module(pets).
pets:move(A,B,C) :- writeln(dog-move(A,B,C)).

注意相关语法 Module:Pred :- ... 在依赖"文件中

Note the relevant syntax Module:Pred :- ... in the 'dependent' files

?- [cat,dog].
%  pets compiled into pets 0.00 sec, 3 clauses
% cat compiled into cat 0.01 sec, 7 clauses
% dog compiled into dog 0.00 sec, 3 clauses
true.

?- test.
Correct to: "pets:test"? yes
pets-move(_G41,_G42,_G43)
move(_G41,_G42,_G43)
cat-move(_G41,_G42,_G43)
move(_G41,_G42,_G43)
dog-move(_G41,_G42,_G43)
move(_G41,_G42,_G43)
true.

?- 

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