是否可以在函数内定义异常 [英] Is it possible to define an exception inside a function

问题描述

在OCaml中实现提前回报"的一种方法是通过异常:

One way to implement "early returns" in OCaml is via exceptions:

exception Exit

let myfunc () = 
    try
      for i = 0 to .... do
        if .. then raise Exit
      done; false
    with Exit -> true

但是，有没有一种方法可以在函数的主体中声明此Exit异常，因此其名称对模块中的其他函数不可见?

However, is there a way to declare this Exit exception in the body of the function, so its name is not visible to other functions in the module?

(* I would like to do this, but it gives a syntax error *)
let myfunc () = 
    exception Exit
    try
      for i = 0 to .... do
        if .. then raise Exit
      done; false
    with Exit -> true

推荐答案

是的，可以通过使用本地模块来实现所需的操作:

Yes, what you want is possible by using a local module:

let myfunc () = 
  let module M = struct exception Exit end in
  try
    for i = 0 to 3 do
      if true then raise M.Exit
    done; false
  with M.Exit -> true

但是，这种风格并不特别令人愉快，因此我不推荐使用.如果要在程序的大多数其余部分中隐藏Exit，则只需在下一个模块界面上显示Exit就足够了.

That style is not particularly pleasant to read, though, so I wouldn't recommend it. It is enough to omit showing Exit at the next module interface if you want to hide it from most of the rest of the program.

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