Pure function aspect?...

[Martin <martin@thedowies.com>]

Now Ada has bitten the bullet and allowed "in out" mode parameters in
functions, is it time to allow users to contract the other extreme and
allow a function to be declared Pure (no state changes, not even
hidden ones)? e.g.

package P is
   type T is tagged private;
   function Pure_F   (Self : T) return Integer
      with Pure;
   function Impure_F (Self : T) return Integer;
private
   type T is tagged record
      I : Integer := 0;
   end record;
end P;


Functions with a Pure contract would be allowed to call other
functions with pure contracts, read values/parameters but promise to
change nothing (not even via 'tricks' a la random number generator!!).

-- Martin