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From: Gautier <Gautier.deMontmollin@Maths.UniNe.CH>
Subject: Re: C like op= proposal
Date: 1999/08/16
Message-ID: <37B7D172.DCE02FFA@Maths.UniNe.CH>#1/1
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Newsgroups: comp.lang.ada
Date: 1999-08-16T00:00:00+00:00
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> It's certainly not any more than syntactic sugar, but if I were designing
> my own Ada like language from scratch, would it be worth including
> such a facility?

Into the language I think it would be an overload. But there
are situation where there is not

  a:= a + 1;
or
  a:= a + b;

which is at the same time more readble than the "++"s macro-assembler
counterparts _and_ transformed into "++"s by optimizers, _but_

  a(b(c,d+e(f,g)).h(i,j)) :=   a(b(c,d+e(f,g)).h(i,j)) + 1;

which can be horribily long and unlikely to be catched by
the optimizer -> 2x too slow (at least: the extra code makes
a penalty for processor cache).

I these cases there are some solutions:

  - A "renames". But you have to make a declare..begin..end block each time :-(
  - Inlined procedures "Inc", "Add" etc. This is much better...

Both solutions may produce code near to a "a(b(c,d+e(f,g)).h(i,j))++" but
it has to be verified.

I'm using a generic Add_Inc package - but I'm sure that a standard
Ada.* equivalent with "intrinsic" pragmas would be the best solution!

generic
     type pm_elt is private;
     one: pm_elt;
     with function "+" (left,right:pm_elt) return pm_elt is <>;
     with function "-" (left,right:pm_elt) return pm_elt is <>;

package Add_Inc is
     procedure Add(a:in out pm_elt; b:pm_elt);
     procedure Sub(a:in out pm_elt; b:pm_elt);
     procedure Inc(a:in out pm_elt);
     procedure Dec(a:in out pm_elt);
end;

package body Add_Inc is
  procedure Add(a:in out pm_elt; b:pm_elt) is begin a:= a+b; end;   
  procedure Sub(a:in out pm_elt; b:pm_elt) is begin a:= a-b; end;
  procedure Inc(a:in out pm_elt) is begin a:=a+one; end;
  procedure Dec(a:in out pm_elt) is begin a:=a-one; end;

  pragma Inline(Add,Sub,Inc,Dec);
end;

-- 
Gautier

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