使用强大的 Ada 枚举功能（以及一些糟糕的输入处理策略，例如异常），您的整个问题一开始就可以避免。您的trans 程序将毫无用处。
如果你对你的枚举值的顺序关系感兴趣，你也可以使用Ada的'First*（第一个枚举字面量），'Last（最后一个枚举文字），'Pos（枚举内的位置），'Succ（下一个枚举文字），'Pred（上一个枚举字面量）。
如果您为变量执行内存映射，您可以使用 'Valid 来检查变量是否具有有效值，并省去对约束错误进行异常捕获的需要。
请看下面的例子：
with Ada.Text_IO; use Ada.Text_IO;
with Ada.Exceptions; use Ada.Exceptions;
procedure Hello is
-- miwing chars and literal values in enum
-- note that jack is 'J' and not the single source code character J
type My_Awesome_Enum is ('1', '2', '3', 'J', Q, K, Ace);
for My_Awesome_Enum use
('1' => -1,
'2' => 2,
'3' => 3,
-- ...
'J' => 11,
Q => 12,
K => 13,
Ace => 14);
temp : Integer;
prev : My_Awesome_Enum;
succ : My_Awesome_Enum;
temp2 : My_Awesome_Enum;
begin
-- ------------------------------------------
-- Ada enum power
declare
begin
for value in My_Awesome_Enum loop
temp := My_Awesome_Enum'Enum_Rep(value);
Put_Line("Enum litteral value: " & value'Image & " - memory representation: " & Integer'Image(temp));
if value /= My_Awesome_Enum'First then
prev := My_Awesome_Enum'Pred(value);
Put_Line("Previous: " & prev'Image);
else
Put_Line("No previous");
end if;
if value /= My_Awesome_Enum'Last then
succ := My_Awesome_Enum'Succ(value);
Put_Line("Next: " & succ'Image);
else
Put_Line("No next");
end if;
Put_Line("");
end loop;
end;
-- ------------------------------------------
-- conversion from some input source
Put_Line("");
declare
strInput : String := "Unknown user value";
begin
Put_Line("Handling of user input: " & strInput);
temp2 := My_Awesome_Enum'Value (strInput);
exception
when E: others =>
Put_Line("Exception catched: " & Exception_Information (E));
Put_Line("Setting value to Ace instead");
temp2 := Ace;
end;
Put_Line("tmp2 value: " & temp2'Image & " - memory representation: " & Integer'Image(My_Awesome_Enum'Enum_Rep(temp2)));
-- ------------------------------------------
-- mmemory mapping
Put_Line("");
declare
my_int : Integer := -3;
mapped_Enum : My_Awesome_Enum;
for mapped_Enum'Address use my_int'Address;
last_enum : My_Awesome_Enum := (My_Awesome_Enum'Last);
stop_condition : Integer := (last_enum'Enum_Rep) + 2;
begin
while (my_int < stop_condition) loop
if mapped_Enum'Valid then
Put_Line("Enum with value: " & my_int'Image & " is valid.");
else
Put_Line("Memory mapping would result in invalid enum for value: " & my_int'Image);
end if;
my_int := my_int + 1;
end loop;
end;
end Hello;
这会给出以下输出（https://www.tutorialspoint.com/compile_ada_online.php，使用 GNATMAKE v7.1.1）：
构建：
$gnatmake -o hello *.adb
gcc -c hello.adb
gnatbind -x hello.ali
gnatlink hello.ali -o hello
执行：
Enum litteral value: '1' - memory representation: -1
No previous
Next: '2'
Enum litteral value: '2' - memory representation: 2
Previous: '1'
Next: '3'
Enum litteral value: '3' - memory representation: 3
Previous: '2'
Next: 'J'
Enum litteral value: 'J' - memory representation: 11
Previous: '3'
Next: Q
Enum litteral value: Q - memory representation: 12
Previous: J
Next: K
Enum litteral value: K - memory representation: 13
Previous: Q
Next: ACE
Enum litteral value: ACE - memory representation: 14
Previous: K
No next
Handling of user input: Unknown user value
Exception catched: raised CONSTRAINT_ERROR : bad input for 'Value: "Unknown user value"
Setting value to Ace instead
tmp2 value: ACE - memory representation: 14
Memory mapping would result in invalid enum for value: -3
Memory mapping would result in invalid enum for value: -2
Enum with value: -1 is valid.
Memory mapping would result in invalid enum for value: 0
Memory mapping would result in invalid enum for value: 1
Enum with value: 2 is valid.
Enum with value: 3 is valid.
Memory mapping would result in invalid enum for value: 4
Memory mapping would result in invalid enum for value: 5
Memory mapping would result in invalid enum for value: 6
Memory mapping would result in invalid enum for value: 7
Memory mapping would result in invalid enum for value: 8
Memory mapping would result in invalid enum for value: 9
Memory mapping would result in invalid enum for value: 10
Enum with value: 11 is valid.
Enum with value: 12 is valid.
Enum with value: 13 is valid.
Enum with value: 14 is valid.
Memory mapping would result in invalid enum for value: 15