syntax - "Variable ... must occur on both sides of this | pattern"

Question

当我在 OCaml 中输入一些代码时，我想同时匹配两种情况(因为我正在编写的函数是可交换的):

type something = 
  | Two of int * int
  | One of int

let my_function p q =
  match p, q with
    | Two (_, _) as two, One (x)
    | One (x), Two (_, _) as two -> (* some value *)
    | _ -> (* some other value *)
;;

我收到以下错误:

Error: Variable two must occur on both sides of this | pattern

当我删除 as 语句时，问题没有发生，但出于逻辑目的我需要它。为什么我不能这样做？我是否必须重写逻辑两次？

Answer 1

as 的优先级低于 ,。因此，您应该在 Two (_,_) as two 两边加上括号。