functional-programming - 如何缩短这个 OCaml 代码？

Question

我只是想知道如何缩短这些代码，因为我怀疑它太多余了

let get ename doc = 
  try Some (StringMap.find ename doc) with Not_found -> None;;

let get_double ename doc = 
  let element = get ename doc in
  match element with
    | None -> None
    | Some (Double v) -> Some v
    | _ -> raise Wrong_bson_type;;

let get_string ename doc = 
  let element = get ename doc in
  match element with
    | None -> None
    | Some (String v) -> Some v
    | _ -> raise Wrong_bson_type;;

let get_doc ename doc = 
  let element = get ename doc in
  match element with
    | None -> None
    | Some (Document v) -> Some v
    | _ -> raise Wrong_bson_type;;

所以，基本上，我有不同类型的值，我将所有这些类型的值放入 map 中。

上面的代码用于从 map 中获取相应类型的值。我所做的是，对于每种类型，我都有一个 get。要获得一种类型的值(value)，我必须看到 a)。它是否存在； b).是否确实是该类型，如果不是，则抛出异常。

但是如您所见，上面的代码似乎是多余的。每种类型的 get 之间的唯一区别只是类型本身。

如何缩短这段代码？

Answer 1

你可以这样做:

let get_generic extract ename doc =
  let element = get ename doc in
  match element with
    | None -> None
    | Some v -> Some (extract v)

let get_double = get_generic (function Double v -> v | _ -> raise Wrong_bson_type)
let get_string = get_generic (function String v -> v | _ -> raise Wrong_bson_type)
let get_doc = get_generic (function Document v -> v | _ -> raise Wrong_bson_type)

编辑:要删除多余的 raise Wrong_bson_type(但它很难看):

let get_generic extract ename doc = try
  let element = get ename doc in
  match element with
    | None -> None
    | Some v -> Some (extract v)
with Match_failure _ -> raise Wrong_bson_type

let get_double = get_generic (fun (Double v) -> v)
let get_string = get_generic (fun (String v) -> v)
let get_doc = get_generic (fun (Document v)-> v)