Ada：编译指示列表

Question

谁能告诉我 Pragma List 的作用（具体来说，什么是“编译列表”）？我不明白 LRM 的描述(2.8.25)

A pragma List takes one of the identifiers On or Off as the single argument. This pragma is allowed anywhere a pragma is allowed. It specifies that listing of the compilation is to be continued or suspended until a List pragma with the opposite argument is given within the same compilation. The pragma itself is always listed if the compiler is producing a listing.

Answer 1

您应该回想一下编译器在 1970 年代后期是如何工作和使用的。我很确定意思和它写的一样简单（用 "outputs" 代替 "is producing"，以获得更现代的措辞）。

with Ada.Text_IO;
--  Now you see me.
pragma List (Off);
--  Now you do not.
private with Some_Secret_Package;
pragma List (On);

package Hello_World is
   ...

Answer 2

编译器可以输出，即“列出”其输入，以及它将生成的任何消息，例如错误消息。当您想要在上下文中清楚、详细地了解消息的内容时，这很有用。 IDE 通常会将 link 消息发送给代码，但即使在今天，考虑到对计算历史的提示，列表也可以逐字指出。使用 pragma List，程序员可以排除不需要列出的内容（如果他或她知道的话）。或者，出于保密原因，排除不应列出的内容。

先是列表，再是原程序正文，pragma List:

Compiling: /some/path/some_proc.adb
Source file time stamp: 2017-01-30 08:30:40
Compiled at: 2017-01-30 09:30:42

     1. procedure Some_Proc is
     2.     procedure Inner;
     3.     --  Does this and that...
     4.
     5.     pragma List (Off);
    10. pragma List (On);
    11.
    12. begin
    13.     Inner (42);
            |
        >>> too many arguments in call to "Inner"

    14. end Some_Proc;

 14 lines: 1 error
gprbuild: *** compilation phase failed

（如果你的编译器是GNAT，在开关中指定-gnatl，用于列表和编译：）

procedure Some_Proc is
    procedure Inner;
    --  Does this and that...

    pragma List (Off);
    procedure Inner is
    begin
        null;
    end Inner;
    pragma List (On);

begin
    Inner (42);
end Some_Proc;

Ada：编译指示列表

Ada: Pragma List

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