为什么在顶层之外的某些语句中需要双分号 [英] Why do I need a double semicolon in some statements outside the toplevel

问题描述

我有以下两行代码:

let a = [1;2;3;4;5;6;7;8;9;0]
print_string (String.concat " " (List.map string_of_int a))

它给了我这个错误:

文件test.ml"，第 65 行，字符 0-0:错误:语法错误

File "test.ml", line 65, characters 0-0: Error: Syntax error

但是，如果我以双分号结束该行:

However, if I end the line with a double semicolon:

let a = [1;2;3;4;5;6;7;8;9;0];;
print_string (String.concat " " (List.map string_of_int a))

效果很好.

我读过，双分号只能用在顶层，所以我为什么要在这里使用它.如果我不这样做，我应该写什么?

I've read, double semicolon should only be used in the top level, so why do I need it here. If I don't, what should I have written instead?

推荐答案

可以使用双分号来引入顶级表达式:

Double semicolons can be used to introduce a toplevel expression:

let x = 0
let do_something () = Printf.printf "x=%d" x
;; do_something ()
;; do_something ()

这里没有分隔 ;; 第一个 do_something() 仍然是函数`do_something 定义的一部分.

Here without the separating ;; the first do_something () would still be part of the definition of the function `do_something.

通常认为使用单元顶级绑定更惯用:

It is generally considered more idiomatic to use an unit toplevel binding:

let x = 0
let do_something () = Printf.printf "x=%d" x
let () =
  do_something (); do_something ()

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