loops - ada中的循环和实现

Question

下面是一段代码，对循环的实现有疑问

               C := character'last; --'// SO code colorizer hack
               I := 1;
               K : loop
                  Done := C = character'first; --'
                  Count2 := I;
                  Exit K when Done;
                  C := character'pred(c);  --'
                  I := I + 1;
               end loop K;

谁能告诉我'K'代表什么。我猜它不是一个变量。'K'如何控制循环的执行？

Answer 1

K是循环的名称。end loopand语句引用该Exit名称，以明确退出哪个循环。

Ada 参考手册称其为“loop_statement_identifier” 。

Answer 2

如前所述，K 是循环的标签。它允许您识别特定循环以提高可读性，并且还可以从一组嵌套的封闭循环中选择性地退出特定循环（即成为“goto”......嘘！:-)

这是一个人为的示例（未编译检查）：

   S : Unbounded_String;
   F : File_Type;
   Done_With_Line : Boolean := False;
   All_Done       : Boolean := False;
begin
    Open(F, In_File, "data_file.dat");
  File_Processor:
    while not End_Of_File(F) loop
        S := Get_Line(F);
       Data_Processor:
        for I in 1 .. Length(S) loop
           Process_A_Character
                (Data_Char => Element(S, I),   -- Mode in
                 Line_Done => Done_With_Line,  -- Mode out
                 Finished  => All_Done);       -- Mode out

           -- If completely done, leave the outermost (file processing) loop
           exit File_Processor when All_Done;

           -- If just done with this line of data, go on to the next one.
           exit Data_Processor when Done_With_Line;
        end loop;
    end loop File_Processor;
    Close(F);
 end;

Answer 3

K is essentially the name of the loop. The exit k tells the code to stop looping and go to the next statement after loop k ends.

You usually don't need to name loops, as you can just say exit and it will exit the enclosing loop. However, if you have a loop nested inside another loop, and you'd like to exit not the one immediately around the exit statement, but the outermost one, then doing something like this may be required.

Answer 4

K 是一个命名循环的标签。哇，好久没看到阿达了……