indexing

	description:
		"Sequential lists, without commitment to a particular representation";

	status: "See notice at end of class";
	names: list, sequence;
	access: index, cursor, membership;
	contents: generic;
	date: "$Date$";
	revision: "$Revision$"

deferred class LIST [G] inherit

	CHAIN [G]
		redefine
			forth
		end

feature -- Cursor movement

	forth is
			-- Move to next position; if no next position,
			-- ensure that `exhausted' will be true.
		deferred
		ensure then
			moved_forth: index = old index + 1
		end;

feature -- Status report

	after: BOOLEAN is
			-- Is there no valid cursor position to the right of cursor?
		do
			Result := (index = count + 1)
		end;

	before: BOOLEAN is
			-- Is there no valid cursor position to the left of cursor?
		do
			Result := (index = 0)
		end;

invariant

	before_definition: before = (index = 0);
	after_definition: after = (index = count + 1);

end -- class LIST


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