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From: Lutz Donnerhacke <lutz@iks-jena.de>
Newsgroups: comp.lang.ada
Subject: Re: Ideas for Ada 200X
Date: Tue, 3 Jun 2003 12:23:57 +0000 (UTC)
Organization: IKS GmbH Jena
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* Preben Randhol wrote:
> Lutz Donnerhacke wrote:
>> Yes, that's the Ada way. But for a lot of simple functions over simple data
>> types, defining such procedures is a pain.
>
> But if the data types are simple do you really need the optimisation?

Let X in "X := X + 4;" be an complicated expression.
Yes, evaluating this expression once or twice is an considerably optimisation.

> If you are adding two matrixes you need to do a lot of other things
> like check if they are of same dimentions etc. and you need to define
> the addition so you might as well do it as a procedure over a "+"
> function.

We are talking about a complex expression used twice in order to perform a
simple one. The function "+" itself is done on simple data types.

The proposal:

  "<>" in the RHS of an assignment is the same as the LHS of this assignment.
  So the LHS determines the type and the location of each occurence of the
  "<>" token in the RHS expression. The process to determine the LHS for every
  use in this statement runs only once.
  So the statement:
    LHS := <> + any_function(<>, ...);
  is equivalent to:
    declare
       X : LHS'Type renames LHS;
    begin
       X := X + any_function(X, ...);
    end;

does not aim to optimization of any simple operation on the RHS, but on the
uniquess of the evaluation of the LHS for the use in the right hand
expression.