indexing
	description: "Circular chains, without commitment to a particular representation"
	status: "See notice at end of class"
	names: circular, ring, sequence
	access: index, cursor, membership
	contents: generic
	date: "$Date$"
	revision: "$Revision$"

deferred class interface
	CIRCULAR [G]

feature -- Access

	cursor: CURSOR
			-- Current cursor position
			-- (from CURSOR_STRUCTURE)

	first: G
			-- Item at position currently defined as first
		require -- from CHAIN
			not_empty: not is_empty

	has (v: like item): BOOLEAN
			-- Does chain include v?
			-- (Reference or object equality,
			-- based on object_comparison.)
			-- (from CHAIN)
		ensure -- from CONTAINER
			not_found_in_empty: Result implies not is_empty

	i_th (i: INTEGER): like item
			-- Item at i-th position
			-- Was declared in CHAIN as synonym of @.
			-- (from CHAIN)
		require -- from TABLE
			valid_key: valid_index (k)

	index: INTEGER
			-- Current cursor index, with respect to position
			-- currently defined as first

	index_of (v: like item; i: INTEGER): INTEGER
			-- Index of i-th occurrence of item identical to v.
			-- (Reference or object equality,
			-- based on object_comparison.)
			-- 0 if none.
			-- (from CHAIN)
		require -- from LINEAR
			positive_occurrences: i > 0
		ensure -- from LINEAR
			non_negative_result: Result >= 0

	item: G
			-- Item at current position
			-- (from TRAVERSABLE)
		require -- from TRAVERSABLE
			not_off: not off
		require -- from ACTIVE
			readable: readable

	last: like first
			-- Item at position currently defined as last
		require -- from CHAIN
			not_empty: not is_empty

	sequential_occurrences (v: G): INTEGER
			-- Number of times v appears.
			-- (Reference or object equality,
			-- based on object_comparison.)
			-- (from LINEAR)
		ensure -- from BAG
			non_negative_occurrences: Result >= 0

	infix "@" (i: INTEGER): like item
			-- Item at i-th position
			-- Was declared in CHAIN as synonym of i_th.
			-- (from CHAIN)
		require -- from TABLE
			valid_key: valid_index (k)

feature -- Measurement

	count: INTEGER
			-- Number of items
			-- (from FINITE)

	index_set: INTEGER_INTERVAL
			-- Range of acceptable indexes
			-- (from CHAIN)
		ensure -- from INDEXABLE
			not_void: Result /= void
		ensure then -- from CHAIN
			count_definition: Result.count = count

	occurrences (v: like item): INTEGER
			-- Number of times v appears.
			-- (Reference or object equality,
			-- based on object_comparison.)
			-- (from CHAIN)
		ensure -- from BAG
			non_negative_occurrences: Result >= 0

	occurrences (v: like item): INTEGER
			-- Number of times v appears.
			-- (Reference or object equality,
			-- based on object_comparison.)
			-- (from CHAIN)
		ensure -- from BAG
			non_negative_occurrences: Result >= 0

feature -- Status report

	after: BOOLEAN
			-- Is there no valid cursor position to the right of cursor?
		ensure then
			empty_and_std_after: Result = (is_empty and standard_after)

	before: BOOLEAN
			-- Is there no valid cursor position to the right of cursor?
		ensure then
			empty_and_std_before: Result = (is_empty and standard_before)

	changeable_comparison_criterion: BOOLEAN
			-- May object_comparison be changed?
			-- (Answer: yes by default.)
			-- (from CONTAINER)

	exhausted: BOOLEAN
			-- Has structure been completely explored?
		ensure -- from LINEAR
			exhausted_when_off: off implies Result

	extendible: BOOLEAN
			-- May new items be added?
			-- (from COLLECTION)

	full: BOOLEAN
			-- Is structure filled to capacity?
			-- (from BOX)

	is_empty: BOOLEAN
			-- Is structure empty?
			-- (from FINITE)

	is_inserted (v: G): BOOLEAN
			-- Has v been inserted by the most recent insertion?
			-- (By default, the value returned is equivalent to calling
			-- `has (v)'. However, descendants might be able to provide more
			-- efficient implementations.)
			-- (from COLLECTION)

	isfirst: BOOLEAN
			-- Is cursor at first position?
			-- (from CHAIN)
		ensure -- from CHAIN
			valid_position: Result implies not is_empty

	islast: BOOLEAN
			-- Is cursor at last position?
			-- (from CHAIN)
		ensure -- from CHAIN
			valid_position: Result implies not is_empty

	object_comparison: BOOLEAN
			-- Must search operations use equal rather than =
			-- for comparing references? (Default: no, use =.)
			-- (from CONTAINER)

	off: BOOLEAN
			-- Is there no current item?
		ensure then
			only_when_empty: Result = is_empty

	prunable: BOOLEAN
			-- May items be removed?
			-- (from COLLECTION)

	readable: BOOLEAN
			-- Is there a current item that may be read?
			-- (from SEQUENCE)

	valid_cursor (p: CURSOR): BOOLEAN
			-- Can the cursor be moved to position p?
			-- (from CURSOR_STRUCTURE)

	valid_cursor_index (i: INTEGER): BOOLEAN
			-- Is i a possible cursor position?
		ensure -- from CHAIN
			valid_cursor_index_definition: Result = ((i >= 0) and (i <= count + 1))
		ensure then
			valid_cursor_index_definition: Result = ((i >= 0) and (i <= count))

	valid_index (i: INTEGER): BOOLEAN
			-- Is i within allowable bounds?
			-- (from CHAIN)
		ensure then -- from INDEXABLE
			only_if_in_index_set: Result implies ((i >= index_set.lower) and (i <= index_set.upper))
		ensure then -- from CHAIN
			valid_index_definition: Result = ((i >= 1) and (i <= count))

	writable: BOOLEAN
			-- Is there a current item that may be modified?
			-- (from SEQUENCE)

feature -- Status setting

	compare_objects
			-- Ensure that future search operations will use equal
			-- rather than = for comparing references.
			-- (from CONTAINER)
		require -- from CONTAINER
			changeable_comparison_criterion
		ensure -- from CONTAINER
			object_comparison

	compare_references
			-- Ensure that future search operations will use =
			-- rather than equal for comparing references.
			-- (from CONTAINER)
		require -- from CONTAINER
			changeable_comparison_criterion
		ensure -- from CONTAINER
			reference_comparison: not object_comparison

feature -- Cursor movement

	back
			-- Move cursor to previous item, cyclically.
		require -- from BILINEAR
			not_before: not before

	finish
			-- Move cursor to last position.
			-- (No effect if empty)
			-- (from CHAIN)
		ensure then -- from CHAIN
			at_last: not is_empty implies islast

	forth
			-- Move cursor to next item, cyclically.
		require -- from LINEAR
			not_after: not after
		ensure then
			moved_forth_at_end: (old index = count) implies (index = 1)

	go_i_th (i: INTEGER)
			-- Move cursor to i-th position from current start, cyclically.
		require -- from CHAIN
			valid_cursor_index: valid_cursor_index (i)
		require else
			index_big_enough: i >= 1
			not_empty: not is_empty
		ensure -- from CHAIN
			position_expected: index = i

	go_to (p: CURSOR)
			-- Move cursor to position p.
			-- (from CURSOR_STRUCTURE)
		require -- from CURSOR_STRUCTURE
			cursor_position_valid: valid_cursor (p)

	move (i: INTEGER)
			-- Move cursor to i-th item from current position,
			-- cyclically.
		ensure -- from CHAIN
			too_far_right: (old index + i > count) implies exhausted
			too_far_left: (old index + i < 1) implies exhausted
			expected_index: (not exhausted) implies (index = old index + i)

	search (v: like item)
			-- Move to first position (at or after current
			-- position) where item and v are equal.
			-- If structure does not include v ensure that
			-- exhausted will be true.
			-- (Reference or object equality,
			-- based on object_comparison.)
			-- (from BILINEAR)
		ensure -- from LINEAR
			object_found: (not exhausted and object_comparison) implies equal (v, item)
			item_found: (not exhausted and not object_comparison) implies v = item

	set_start
			-- Define current position as the first.
		require
			not_empty: not is_empty

	start
			-- Move cursor to first position.
			-- (No effect if empty)
			-- (from CHAIN)
		ensure then -- from CHAIN
			at_first: not is_empty implies isfirst

feature -- Element change

	append (s: SEQUENCE [G])
			-- Append a copy of s.
			-- (from SEQUENCE)
		require -- from SEQUENCE
			argument_not_void: s /= void
		ensure -- from SEQUENCE
			new_count: count >= old count

	extend (v: G)
			-- Add a new occurrence of v.
			-- (from BAG)
		require -- from COLLECTION
			extendible: extendible
		ensure -- from COLLECTION
			item_inserted: is_inserted (v)
		ensure then -- from BAG
			one_more_occurrence: occurrences (v) = old (occurrences (v)) + 1

	fill (other: CONTAINER [G])
			-- Fill with as many items of other as possible.
			-- The representations of other and current structure
			-- need not be the same.
			-- (from COLLECTION)
		require -- from COLLECTION
			other_not_void: other /= void
			extendible

	force (v: like item)
			-- Add v to end.
			-- (from SEQUENCE)
		require -- from SEQUENCE
			extendible: extendible
		ensure then -- from SEQUENCE
			new_count: count = old count + 1
			item_inserted: has (v)

	put (v: like item)
			-- Replace current item by v.
			-- (Synonym for replace)
			-- (from CHAIN)
		require -- from COLLECTION
			extendible: extendible
		ensure -- from COLLECTION
			item_inserted: is_inserted (v)
		ensure then -- from CHAIN
			same_count: count = old count

	put_i_th (v: like item; i: INTEGER)
			-- Put v at i-th position.
			-- (from CHAIN)
		require -- from TABLE
			valid_key: valid_index (k)
		ensure then -- from INDEXABLE
			insertion_done: i_th (k) = v

	replace (v: G)
			-- Replace current item by v.
			-- (from ACTIVE)
		require -- from ACTIVE
			writable: writable
		ensure -- from ACTIVE
			item_replaced: item = v

feature -- Removal

	prune (v: like item)
			-- Remove the first occurrence of v if any.
			-- If no such occurrence go off.
			-- (from SEQUENCE)
		require -- from COLLECTION
			prunable: prunable

	prune_all (v: like item)
			-- Remove all occurrences of v; go off.
			-- (from SEQUENCE)
		require -- from COLLECTION
			prunable
		ensure -- from COLLECTION
			no_more_occurrences: not has (v)

	remove
			-- Remove item at cursor position.
			-- Move cursor to right neighbor (cyclically).
			-- If removed item was at current starting position,
			-- move starting position to right neighbor.
		require -- from ACTIVE
			prunable: prunable
			writable: writable

	wipe_out
			-- Remove all items.
			-- (from COLLECTION)
		require -- from COLLECTION
			prunable
		ensure -- from COLLECTION
			wiped_out: is_empty

feature -- Transformation

	swap (i: INTEGER)
			-- Exchange item at i-th position with item
			-- at cursor position.
			-- (from CHAIN)
		require -- from CHAIN
			not_off: not off
			valid_index: valid_index (i)
		ensure -- from CHAIN
			swapped_to_item: item = old i_th (i)
			swapped_from_item: i_th (i) = old item

feature -- Conversion

	linear_representation: LINEAR [G]
			-- Representation as a linear structure
			-- (from LINEAR)

feature -- Duplication

	duplicate (n: INTEGER): like Current
			-- Copy of sub-chain beginning at current position
			-- and having min (n, from_here) items,
			-- where from_here is the number of items
			-- at or to the right of current position.
			-- (from CHAIN)
		require -- from CHAIN
			not_off_unless_after: off implies after
			valid_subchain: n >= 0

feature -- Iteration

	do_all (action: PROCEDURE [ANY, TUPLE [G]])
			-- Apply action to every item.
			-- Semantics not guaranteed if action changes the structure;
			-- in such a case, apply iterator to clone of structure instead.
			-- (from LINEAR)
		require -- from TRAVERSABLE
			action_exists: action /= void

	do_if (action: PROCEDURE [ANY, TUPLE [G]]; test: FUNCTION [ANY, TUPLE [G], BOOLEAN])
			-- Apply action to every item that satisfies test.
			-- Semantics not guaranteed if action or test changes the structure;
			-- in such a case, apply iterator to clone of structure instead.
			-- (from LINEAR)
		require -- from TRAVERSABLE
			action_exists: action /= void
			test_exits: test /= void

	for_all (test: FUNCTION [ANY, TUPLE [G], BOOLEAN]): BOOLEAN
			-- Is test true for all items?
			-- (from LINEAR)
		require -- from TRAVERSABLE
			test_exits: test /= void

	there_exists (test: FUNCTION [ANY, TUPLE [G], BOOLEAN]): BOOLEAN
			-- Is test true for at least one item?
			-- (from LINEAR)
		require -- from TRAVERSABLE
			test_exits: test /= void

invariant

	not_before_unless_empty: before implies is_empty
	not_after_unless_empty: after implies is_empty
	not_off_unless_empty: off implies is_empty
		-- from ANY
	reflexive_equality: standard_is_equal (Current)
	reflexive_conformance: conforms_to (Current)
		-- from CHAIN
	non_negative_index: index >= 0
	index_small_enough: index <= count + 1
	off_definition: off = ((index = 0) or (index = count + 1))
	isfirst_definition: isfirst = ((not is_empty) and (index = 1))
	islast_definition: islast = ((not is_empty) and (index = count))
	item_corresponds_to_index: (not off) implies (item = i_th (index))
	index_set_has_same_count: index_set.count = count
		-- from ACTIVE
	writable_constraint: writable implies readable
	empty_constraint: is_empty implies (not readable) and (not writable)
		-- from INDEXABLE
	index_set_not_void: index_set /= void
		-- from BILINEAR
	not_both: not (after and before)
	before_constraint: before implies off
		-- from LINEAR
	after_constraint: after implies off
		-- from TRAVERSABLE
	empty_constraint: is_empty implies off
		-- from FINITE
	empty_definition: is_empty = (count = 0)
	non_negative_count: count >= 0

indexing
	library: "[
			EiffelBase: Library of reusable components for Eiffel.
	]"
	status: "[
			Copyright 1986-2001 Interactive Software Engineering (ISE).
			For ISE customers the original versions are an ISE product
			covered by the ISE Eiffel license and support agreements.
	]"
	license: "[
			EiffelBase may now be used by anyone as FREE SOFTWARE to
			develop any product, public-domain or commercial, without
			payment to ISE, under the terms of the ISE Free Eiffel Library
			License (IFELL) at http://eiffel.com/products/base/license.html.
	]"
	source: "[
			Interactive Software Engineering Inc.
			ISE Building
			360 Storke Road, Goleta, CA 93117 USA
			Telephone 805-685-1006, Fax 805-685-6869
			Electronic mail <info@eiffel.com>
			Customer support http://support.eiffel.com
	]"
	info: "[
			For latest info see award-winning pages: http://eiffel.com
	]"

end -- class CIRCULAR