模块内部的多晶型(OCaml)

Question

我只是定义一个Matrix模块如下:

module Matrix =
  struct
    type element
    type t = element array array

    let make (nr: int) (nc: int) (init: element) : t =
      let result = Array.make nr (Array.make nc init) in
      for i = 0 to nr - 1 do
        result.(i) <- Array.make nc init
      done;
      result
  end

并let m = Matrix.make 3 4 0给我一个错误Error: This expression has type int but an expression was expected of type Matrix.element.然后我补充说'a:

module Matrix =
  struct
    type element = 'a
    type t = element array array

    let make (nr: int) (nc: int) (init: element) : t =
      let result = Array.make nr (Array.make nc init) in
      for i = 0 to nr - 1 do
        result.(i) <- Array.make nc init
      done;
      result
  end

模块的编译给出了错误Error: Unbound type parameter 'a.

谁能告诉我如何定义模块内部的类型？

Answer 1

两个问题:(1)类型变量不能通过绑定命名,就像你试过的那样element,(2)你的类型t需要将所有类型变量作为参数,如果它应该是多态的.也就是说,你要么想写

type 'a t = 'a array array

或者您必须将模块转换为仿函数,并将其element作为整个模块的参数.