创建一个模块以便在ocaml中打印嵌套函数

Question

我有这样的类型：

type lT = LV of name
        | LC of name
        | LA of lT * lT
        | LAb of name  * lT

我想以一种方式实现一个叫做s的函数，它将以以下方式运行：

let println x = printf "%s\n" (s x)
s (`App(`App(`App(`Bs, `K), `K), `K))  ==>  "B* K K K”

因此，我实现了以下模块：

module type L2C = 
sig
  val c1 : lT -> ([> `T | `L | `J
                        | `A of 'b * 'b | `V of name | `C of name] as 'b)

  val c2 : lT -> ([> `T | `L | `J | `C | `D
                        | `A of 'b * 'b | `V of name | `C of name] as 'b)

  val c3 : lT -> ([> `T | `L | `J | `C | `D | `Sp | `Bp | `Bs | `Cp
                        | `A of 'b * 'b | `V of name | `C of name] as 'b)

  val e : ([< `T | `L | `J | `C | `D | `Sp | `Bp | `Bs | `Cp
                        | `A of 'b * 'b | `V of name | `C of name] as 'b) ->
             ([ `T | `L | `J | `C | `D | `Sp | `Bp | `Bs | `Cp
                        | `A of 'b * 'b | `V of name | `C of name] as 'b)
end

但是由于我是ocaml的新手，所以我无法创建“ s”函数来获得所需的输出。

这样做的可能方法是什么？

Answer 1

我不太了解您要执行的操作的详细信息，但我希望这可以有所帮助：

let s expr =
  let rec loop acc = function
    | `Bs -> "B* "^acc
    | `K -> "K "^acc
    | `App(a,b) -> (loop acc a)^(loop acc b)
  in
  loop "" expr

上面对于您给出的示例非常有效：

s (`App(`App(`App(`Bs, `K), `K), `K));;

- : string = "B* K K K "

如果需要有用的类型推断，而不是难看的多态变体类型，则需要在模式匹配中添加额外的大小写，并可能添加一些类型注释。

Answer 2

如果您不必坚持：

s (`App(`App(`App(`Bs, `K), `K), `K))  ==>  "B* K K K”

您可以使用ppx_deriving自动生成一个将您的类型转换为字符串的函数（下面的utop中的示例）：

#require "ppx_deriving.std";;
type t = [`App of (t * t) | `B | `K] [@@deriving show];; (* assuming your type is like this *)
> type t = [ `App of t * t | `B | `K ]
> val pp : Format.formatter -> t -> unit = <fun>
> val show : t -> string = <fun> ...
show (`App (`B , `App (`K , `K)));;
- : string = "`App ((`B, `App ((`K, `K))))"