OCaml:设置模块 [英] OCaml: Set modules

问题描述

我想使用OCaml生成数据集并在它们之间进行比较.我看过有关Set.OrderType，Set.Make等模块类型的文档，但是我不知道如何初始化集合或以其他方式使用它们.

I want to use OCaml to generates sets of data and make comparisons between them. I have seen the documentation for Module types like Set.OrderType, Set.Make, etc, but I can't figure out how to initialize a set or otherwise use them.

推荐答案

使用函数接口定义集合.对于任何给定的类型，必须使用Set.Make函子为该类型创建一个Set模块.不幸的是，标准库没有为内置类型定义Set实例.在大多数简单情况下，使用Pervasives.compare就足够了.这是适用于int的定义:

Sets are defined using a functorial interface. For any given type, you have to create a Set module for that type using the Set.Make functor. An unfortunate oversight of the standard libraries is that they don't define Set instances for the built-in types. In most simple cases, it's sufficient to use Pervasives.compare. Here's a definition that works for int:

module IntSet = Set.Make( 
  struct
    let compare = Pervasives.compare
    type t = int
  end )

模块IntSet将实现Set.S接口.现在，您可以使用IntSet模块对集合进行操作:

The module IntSet will implement the Set.S interface. Now you can operate on sets using the IntSet module:

let s = IntSet.empty ;;
let t = IntSet.add 1 s ;;
let u = IntSet.add 2 s ;;
let tu = IntSet.union t u ;;

请注意，您不必将Set.Make的输入结构明确定义为OrderedType；类型推断将为您完成工作.另外，您可以使用以下定义:

Note that you don't have to explicitly define the input structure for Set.Make as an OrderedType; type inference will do the work for you. Alternatively, you could use the following definition:

module IntOrder : Set.OrderedType = struct
  type t = int
  let compare = Pervasives.compare
end

module IntSet = Set.Make( IntOrder )

这样的好处是您可以重新使用同一模块来实例化Map:

This has the advantage that you can re-use the same module to instantiate a Map:

module IntMap = Map.Make( IntOrder )

使用函子会失去一些通用性，因为元素的类型是固定的.例如，您将无法定义一个函数，该函数采用某种任意类型的Set并对其执行某些操作. (幸运的是，Set模块本身在Set上声明了许多有用的操作.)

You lose some genericity in using functors, because the type of the elements is fixed. For example, you won't be able to define a function that takes a Set of some arbitrary type and performs some operation on it. (Luckily, the Set module itself declares many useful operations on Sets.)

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