Re: Gnat GPL 2010 available soon (conditional expressions)

["Randy Brukardt" <randy@rrsoftware.com>]

"Peter C. Chapin" <pcc482719@gmail.com> wrote in message 
news:4c276114$0$2378$4d3efbfe@news.sover.net...
...
> 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);
>
> I might be able to quickly tell which complicated expression I need to
> look at without having to study both.

Note that one advantage of conditional expressions is that they can avoid 
duplicating code. For instance,

X(Index_Expression*Index_Base + 1) :=
   (if Condition then
         Complicated_Expression
    else
         Other_Complicated_Expression);

Probably is preferable to

if Condition then
   X(Index_Expression*Index_Base + 1) := Complicated_Expression;
else

   X(Index_Expression*Index_Base - 1) := Other_Complicated_Expression;
end if;

because it is much less likely to have a subtle error (like the second 
example I wrote above). I find that I write quite a bit of code of the 
second form, and I know I'd save time debugging if I had the first.

                                   Randy.

P.S. But the resolution of conditional expressions is surprisingly complex. 
I think we've got it right, finally.