description: "Multi-level undo mechanism"
	author: "Patrick Schoenbach"

deferred class interface

feature -- Measurement

	commands_remembered: INTEGER
			-- Number of commands actually remembered

	history_capacity: INTEGER
			-- Capacity of command history
feature -- Status report

	is_recording: BOOLEAN
			-- Is mechanism recording a history entry at the moment?
			-- (from UNDO_MECHANISM)

	redoable: BOOLEAN
			-- Is there a redoable command in the history?

	undoable: BOOLEAN
			-- Is there an undoable command in the history?
feature -- Basic operations

			-- Redo command.
			-- (from UNDO_MECHANISM)
		require -- from UNDO_MECHANISM
			redoable_command: redoable;
			not_recording: not is_recording

			-- Undo command.
			-- (from UNDO_MECHANISM)
		require -- from UNDO_MECHANISM
			undoable_command: undoable;
			not_recording: not is_recording

		-- from GENERAL
	reflexive_equality: standard_is_equal (Current);
	reflexive_conformance: conforms_to (Current);
	history_exists: history /= void;

end -- class MULTI_LEVEL_UNDO