----------------------------------------------------------------------------
-- PACKAGE:
--      Abstract_Sets
-- AUTHOR:
--      Yoav Tzruya
-- EXPRTED TYPES:
--      Set - A generic (on set_element) controlled set of elements 
-- EXPORTED PROCEDURES:
--      Empty - return an empty set
--      Unit  - return a set of one element
--      Union - unify two sets into one (no duplicates of course)
--      Intersection - the intersection of two sets.
--      Take         - take an arbitrary element out of the set.
--      to_string    - represent the set by a string of chars.
-- EXPORTED EXCEPTIONS:
--      set_is_empty_exception - may be raised by the Take procedure when
--              trying to take an element out of the empty set.
----------------------------------------------------------------------------

-- ** SPECIFICATION IMPORTS **
with Ada.Finalization;

generic
        -- the generic element of the set
        type Set_Element is private;

        -- a function to convert one element to a string
        with function to_string (
                        element_arg : in     set_element )
             return string;

package Abstract_Sets is

        -- ** EXPORTED EXCEPTIONS **

        set_is_empty_exception : exception;

        -- ** EXPORTED TYPES **

        type Set is abstract new Ada.Finalization.Controlled with private;


        -- ** EXPORTED SUBPROGRAMS **

        function Empty
                return Set is abstract;
                -- empty set

        function Unit (
                        Element : in     Set_Element)
                return Set is abstract;
                -- build set with 1 element

        function Union (
                        Left  : in    Set;
                        Right : in    Set)
                return Set is abstract;

        function Intersection (
                        Left  : in    Set;
                        Right : in    Set)
                return Set is abstract;

        procedure Take (
                        From    : in out Set;
                        Element :    out Set_Element)
                 is abstract;

        function to_string (
                        set_arg : in     set'class)
                return string;

private
        type Set is abstract new Ada.Finalization.Controlled with null record;
end Abstract_Sets;