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From: "Steve" <nospam_steved94@comcast.net>
Newsgroups: comp.lang.ada
References: 
 <18b41828-bda4-4484-8884-ad62ce1c831d@f36g2000hsa.googlegroups.com>
Subject: Re: and then... (a curiosity)
Date: Mon, 1 Sep 2008 20:41:33 -0700
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Date: 2008-09-01T20:41:33-07:00
List-Id: <comp.lang.ada>

"mockturtle" <framefritti@gmail.com> wrote in message 
news:18b41828-bda4-4484-8884-ad62ce1c831d@f36g2000hsa.googlegroups.com...
> Dear.all,
> today while I was writing in my favorite language
> (PERL with C extensions, of course :-)))) I wondered why in Ada the
> "shortcut and"  is "and then", while the simple "and" has not
> a shortcut  behaviour.  My curiosity stems from the fact that
> I am not able to envision any situation where the "non shortcut"
> version would preferable, but I immagine that there was some
> reason for this choice.  Do anyone have any hint?
>
> Thank you in advance.

There are cases where both arguments to an "and" operator should always be 
used.  For example if you have Function A and Functon B involved in a 
condition:

  if A(x) and B(y) then
    ... do something
  end if;

If short circuit evalution is permitted then more complex logic is required 
to assure that both arguments are evaluated:

  resultA := A(x);
  resultB := B(z);
  if resultA and resultB then
    ... do something
  end if;

With Ada you can choose whether or not you want short circuit evaluation. 
If you require short circuit evaluation you must convey that information to 
the compiler.  If you do not require short circuit evaluation you can convey 
that information as well.  The more the compiler knows about your 
requirements, the greater the potential for optimization.

The form used also conveys information about the code to programmers reading 
the code.

Regards,
Steve