尝试进一步了解OCaml的接口/模块 [英] Try to further understanding the interface/module of OCaml

问题描述

我在OCaml中理解了 interfaces 和 module 的概念。

现在我明白如何使用它们了。

然而，我不明白如何充分利用它们。

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例如，在Java中，假设我们有一个接口 Map ，并且我们还有 Hashtable 和 HashMap ，它们实现了 Map 。

我可以这样做：

  Map m = new Hashtable（）; 
 m.put（key，value）; 
  

有一天，如果我改变了主意，可以改为 Hashmap Map m = new Hashtable（）; 为 Map m = new HashMap（）; c>，对吗？

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但是我怎么能在Ocaml中轻松做到这一点？ MapSig 和'HashMap：MapSig 和Hashtable：MapSig code> in OCaml。

如何轻松更改实施？

我不认为我可以，因为在OCaml中我必须这样做：

  let m = Hashtable.create（ ）;; 
 
 Hashtable.put m键值;; 
  

如果我我想用 HashMap 代替每一个 Hashtable 和 HashMap $ b

编辑：

我不仅在寻找一种对模块进行别名的方法，我还考虑了im的有效性例如，在上面的Java示例中，只有 HashMap 已经实现了 Map 接口，我可以用 HashMap Hashtable >。否则，Java编译器会报错。

但是如果我在OCaml中执行 module M = Hashtable ，并且 HashMap 不会跟随 MapSig ，而用<$ c替换 Hashtable $ c> HashMap ，会发生什么？我认为编译器不会抱怨，对吗？

解决方案

下面是一个示例，显示我认为您要求的内容：

 ＃模块类型HASH = sig类型t val哈希值：t  - > int end ;; 
模块类型HASH = sig类型t val哈希值：t  - > int end 
＃module I = struct type t = int let hash i = i end ;; 
模块I：sig类型t = int val哈希：'a  - > 'a end 
＃module J = struct type t = int end ;; 
模块J：sig类型t = int结束
＃模块M：HASH = I ;; 
模块M：HASH 
＃模块N：HASH = J ;; 
错误：签名不匹配：
模块不匹配：sig类型t = int结束不包含在HASH 
字段`hash'是必需的但未提供
  

额外的：HASH 指定模块必须匹配HASH签名（它也限制了它的签名）。

就像一面评论，我相信OCaml模块系统以其表现力而闻名于世（至少在模块系统界）。我仍然是初学者，但值得研究。

I understand in OCaml there are concepts of interfaces and module.

And I understand how to use them now.

However, what I don't understand is how to fully utilise them.

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For example, in Java, let's say we have a interface Map and we also have Hashtable and HashMap that implement Map.

In code, I can do like:

Map m = new Hashtable();
m.put("key", value);

Someday, if I change my mind, I can change to Hashmap very quickly by changing Map m = new Hashtable(); to Map m = new HashMap();, right?

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But how can I easily do that in Ocaml?

For example, I have MapSig and 'HashMap:MapSigand "Hashtable:MapSig in OCaml.

How can I change the implementation easily?

I don't think I can because in OCaml I have to do like:

let m = Hashtable.create ();;

Hashtable.put m key value;;

if I want to use HashMap instead, I have to replace every Hashtable with HashMap in the code, right?

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Edit:

I am not only seeking a way to make a alias to modules. I also consider the validity of implementations, i.e., whether the implementation follow the desired interface.

For example, in above Java example, only if HashMap has implemented Map interface, I can replace Hashtable with HashMap. otherwise, Java compiler will complain.

but if I do module M = Hashtable in OCaml, and if HashMap does not follow MapSig and I replace Hashtable with HashMap, what will happen? I think compiler won't complain, right?

解决方案

Here's an example that shows what I think you're asking for:

# module type HASH = sig type t val hash : t -> int end ;;
module type HASH = sig type t val hash : t -> int end
# module I = struct type t = int let hash i = i end ;;
module I : sig type t = int val hash : 'a -> 'a end
# module J = struct type t = int end ;;
module J : sig type t = int end
# module M : HASH = I ;;
module M : HASH
# module N : HASH = J ;;
Error: Signature mismatch:
       Modules do not match: sig type t = int end is not included in HASH
       The field `hash' is required but not provided

The extra ": HASH" specifies that the module must match the HASH signature (and it also restricts it to that signature).

Just as a side comment, I believe the OCaml module system is world famous for its expressivity (at least in module system circles). I'm still a beginner at it, but it is worth studying.

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