Re: 4 beginner's questions on the PL Ada

[Adam Beneschan <adambeneschan@aol.com>]

On Friday, August 9, 2013 9:50:53 AM UTC-7, Emanuel Berg wrote:
> 1. How do you make a constant in Ada? Can I make one that is
> computed, for example an integer, set to Milliseconds(something)?

   Some_Constant : constant integer := <expression>.  The expression can be any expression that can be computed.

 
> 2. How do you get options from the CL? I.e., how do you do the C 
> argv in Ada?

Ada.Command_Line.  http://www.ada-auth.org/standards/12rm/html/RM-A-15.html

 
> 3. Is it possible to get the task *name* (from the code) into a 
> string, programatically? That way, a generic procedure could be
> used to communicate from tasks, with Put_Line, and without having
> to hard code the task name every time.

No, not really.  One thing to keep in mind is that Ada has task *types*, so that you can declare a task type and then start any number of tasks of that type.  And the tasks don't have to be associated with variables; you can start an array of tasks:

   type Task_Array is array (1 .. 10) of Task_Type;
   T : Task_Array;

will start 10 tasks, and they won't really have names.  Well, I guess you can call them T(1), T(2), ...  But tasks can also be record components, and you can have accesses to tasks, so there really isn't a concept of a "name" for a task.  So if you want to give tasks a name, you'll have to do this in the program.


> 4. How do you exit Ada altogether? For example, if there are 3 
> tasks, and one solves the problem, how can I terminate the whole
> application at once? (Rather than sending messages to all the
> tasks, "OK, we're done looking!")

I don't recommend having one task kill the entire program.  Ada allows you to define types that have finalization procedures associated with them (e.g. for a file, you might want a finalization procedure that makes sure any remaining data is flushed to the file).  Ada makes sure that when a procedure or task is exited, anything that needs to be finalized will be finalized.  Performing an operation that just exits the program suddenly will subvert that.  There's an "abort" statement to allow one task to terminate other tasks; that *does* ensure that finalization takes place.  But overall, I think it's better to do things cleanly; one way is to send a message to the other tasks with entry calls, but you can also create a variable (or a protected object) that's accessible to all tasks that they can check at certain points to see if they can quit.

                               -- Adam