Re: Gnat GPL 2010 available soon (conditional expressions)

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On Sun, 27 Jun 2010 10:35:02 -0400, Peter C. Chapin wrote:

> Also I find that when skimming program text just knowing that something
> is conditional is sometimes enough for me to decide if I have to read it
> more closely or not. If it says
> 
> X := (if Rare_Condition then
>          Complicated_Expression
>       else
>          Complicated_Expression);

In comparable cases earlier Ada's choices were opposite:

   Complicated_Expression and then Complicated_Expression
   Complicated_Expression or else Complicated_Expression
   (Type with Complicated_List)

> I might be able to quickly tell which complicated expression I need to
> look at without having to study both.

Do not use complicated expressions, that is the point! Note that you have
to format the expression so that it looked like a normal if. What is the
gain? It is unreadable when written as one line. It is as verbose as normal
if when formatted. And it does not save you writing a function in real-life
cases:

   File_Name := <add extension ".txt" if absent, do lower case, remove
forward "./"> Argument (1);

> Of course it all comes down to what one is used to. Dmitry says the
> leading 'if' makes things harder to read, but I find his examples much
> more difficult.

If you like prefix notation, then why not:

generic -- Built-in intrinsic generic for each type
   Type (<>) is limited private;
function "if" (Condition : Boolean; Then, Else : Type) return Type;

used as:

   if (A, B, C)
   if (A, then => B, else => C)

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de