带有Core_unix.exec的OCaml Core_unix.fork永不返回

Question

我在以以下方式执行fork时遇到麻烦，因为子进程返回a Core_kernel.Std.never_returns，而父进程试图返回()。

我得到了错误This expression has type unit but an expression was expected of type Core_kernel.Std.never_returns = Core_kernel.Nothing0.t。似乎找不到使用的正确方法Core.Std。

open Core.Std
open Unix

let () = 
  let prog = "ls" in
  let args = ["ls"; "-l"] in
  match Unix.fork () with
  | `In_the_child ->
     Unix.exec ~prog:prog ~args:args ();
  | `In_the_parent _ ->
     (* continue on with the program *)

Answer 1

该never_returns类型是专门为never_returns功能性消费而设计的。这就要求程序员在代码中清楚地说明，他明白表达式不会终止。这是一个工作示例：

let () =
  let prog = "ls" in
  let args = ["ls"; "-l"] in
  match Unix.fork () with
  | `In_the_child ->
    Unix.exec ~prog ~args () |>
    never_returns
  | `In_the_parent _ -> ()