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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: Defining a binary operator between function access types: Is it
  possible?
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Date: Thu, 16 Oct 2008 16:26:49 +0200
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Date: 2008-10-16T16:26:49+02:00
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On Thu, 16 Oct 2008 06:34:30 -0700 (PDT), soychangoman@gmail.com wrote:

> I'm trying to define a binary operator between function access types
> that returns the access to the function that is the binary operator
> acting on both functions.

You cannot create a new subprograms and return it from another subprogram.
To have the effect of an interpreted language you have to define
corresponding first-class types. For example:

   type Operation is abstract tagged private;
   function Evaluate (F : Operation; X : Real) return Real is abstract;
   ...
   type Squaring is new Operation with null record;
   overriding function Evaluate (F : Squaring; X : Real) return Real;
   Square : constant Squaring;
   ...

   type Composed_By_Plus is new Operation with private;
   function "+" (L, R : Operation'Class) return Composed_By_Plus;
   overriding
      function Evaluate (F : Composed_By_Plus; X : Real) return Real;
   ...

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