On Tue, 28 Jul 2015, EGarrulo wrote:

> On Tuesday, July 28, 2015 at 2:54:50 PM UTC+2, Dmitry A. Kazakov wrote:
>
>> You can inline the suggested wrapper and hope that the compiler indeed does
>> inlining than effectively will make it lazily evaluated.
>
> I can't understand what you mean here.  Would you please explain
> further?  Thank you.

I am not Dmitry, but here is what I frequently do (I actually have a 
package Debug for that). The declaration is as follows:

procedure Trace(Do_It: Boolean; Message: String) with Inline;

The implementation is

procedure Trace(Do_It: Boolean; Message: String) is
begin
   if Do_It then
       Ada.Text_IO.Put_Line(Trace_File, Message);
   end if;
end Trace;

In your program, you just write

Me_Active: Constant Boolean := True;
   -- change this to False if you don't want to trace Me.

Debug.Trace(Me_Active, "Performing Step " & Step(Me));

Now the compiler (well, gnat -- I have no clue what other compilers will 
do) will first inline the code inside Debug.Trace and, if Active_Me is 
False, and the function Step has no side effects, the compiler will 
eliminate the dead code -- at least, if you switch on the optimization.

Actually, this is *not* lazy evaluation: If Step has side effects, Ada 
requires to evaluate it, even if Me_Active is False. A lazy language would 
not evaluate Step. But in the given case, who would want to call some 
function Step with side effects?


--------  I  love  the  taste  of  Cryptanalysis  in  the morning!  --------
www.uni-weimar.de/de/medien/professuren/mediensicherheit/people/stefan-lucks
----Stefan.Lucks (at) uni-weimar.de, Bauhaus-Universität Weimar, Germany----