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indexing
	description: "[
		Possibly circular sequences of items,
		without commitment to a particular representation
	]"
	status: "See notice at end of class"
	names: chain, sequence
	access: index, cursor, membership
	contents: generic
	date: "$Date: 2001-11-16 20:32:23 +0000 (Fri, 16 Nov 2001) $"
	revision: "$Revision: 51435 $"

deferred class 
	CHAIN [G]

feature -- Access

	cursor: CURSOR is
			-- Current cursor position
			-- (from CURSOR_STRUCTURE)
		deferred
		end

	first: like item is
			-- Item at first position
		require
			not_empty: not is_empty
		local
			pos: CURSOR
		do
			pos := cursor
			start
			Result := item
			go_to (pos)
		end

	has (v: like item): BOOLEAN is
			-- Does chain include v?
			-- (Reference or object equality,
			-- based on object_comparison.)
		local
			pos: CURSOR
		do
			pos := cursor
			Result := sequential_has (v)
			go_to (pos)
		ensure -- from CONTAINER
			not_found_in_empty: Result implies not is_empty
		end

	i_th (i: INTEGER): like item is
			-- Item at i-th position
			-- Was declared in CHAIN as synonym of @.
		require -- from TABLE
			valid_key: valid_index (k)
		local
			pos: CURSOR
		do
			pos := cursor
			go_i_th (i)
			Result := item
			go_to (pos)
		end

	index: INTEGER is
			-- Current cursor index
		deferred
		end

	index_of (v: like item; i: INTEGER): INTEGER is
			-- Index of i-th occurrence of item identical to v.
			-- (Reference or object equality,
			-- based on object_comparison.)
			-- 0 if none.
		require -- from LINEAR
			positive_occurrences: i > 0
		local
			pos: CURSOR
		do
			pos := cursor
			Result := sequential_index_of (v, i)
			go_to (pos)
		ensure -- from LINEAR
			non_negative_result: Result >= 0
		end

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

	last: like item is
			-- Item at last position
		require
			not_empty: not is_empty
		local
			pos: CURSOR
		do
			pos := cursor
			finish
			Result := item
			go_to (pos)
		end

	sequential_occurrences (v: G): INTEGER is
			-- Number of times v appears.
			-- (Reference or object equality,
			-- based on object_comparison.)
			-- (from LINEAR)
		do
			from
				start
				search (v)
			until
				exhausted
			loop
				Result := Result + 1
				forth
				search (v)
			end
		ensure -- from BAG
			non_negative_occurrences: Result >= 0
		end

	infix "@" (i: INTEGER): like item is
			-- Item at i-th position
			-- Was declared in CHAIN as synonym of i_th.
		require -- from TABLE
			valid_key: valid_index (k)
		local
			pos: CURSOR
		do
			pos := cursor
			go_i_th (i)
			Result := item
			go_to (pos)
		end
	
feature {NONE} -- Access

	sequential_has (v: like item): BOOLEAN is
			-- Does structure include an occurrence of v?
			-- (Reference or object equality,
			-- based on object_comparison.)
			-- (from LINEAR)
		do
			start
			if not off then
				search (v)
			end
			Result := not exhausted
		ensure -- from CONTAINER
			not_found_in_empty: Result implies not is_empty
		end

	sequential_index_of (v: like item; i: INTEGER): INTEGER is
			-- Index of i-th occurrence of v.
			-- 0 if none.
			-- (Reference or object equality,
			-- based on object_comparison.)
			-- (from LINEAR)
		require -- from LINEAR
			positive_occurrences: i > 0
		local
			occur, pos: INTEGER
		do
			if object_comparison and v /= void then
				from
					start
					pos := 1
				until
					off or (occur = i)
				loop
					if item /= void and then v.is_equal (item) then
						occur := occur + 1
					end
					forth
					pos := pos + 1
				end
			else
				from
					start
					pos := 1
				until
					off or (occur = i)
				loop
					if item = v then
						occur := occur + 1
					end
					forth
					pos := pos + 1
				end
			end
			if occur = i then
				Result := pos - 1
			end
		ensure -- from LINEAR
			non_negative_result: Result >= 0
		end

	sequential_search (v: like item) is
			-- Move to first position (at or after current
			-- position) where item and v are equal.
			-- (Reference or object equality,
			-- based on object_comparison.)
			-- If no such position ensure that exhausted will be true.
			-- (from LINEAR)
		do
			if object_comparison and v /= void then
				from
				until
					exhausted or else (item /= void and then v.is_equal (item))
				loop
					forth
				end
			else
				from
				until
					exhausted or else v = item
				loop
					forth
				end
			end
		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
		end
	
feature -- Measurement

	count: INTEGER is
			-- Number of items
			-- (from FINITE)
		deferred
		end

	index_set: INTEGER_INTERVAL is
			-- Range of acceptable indexes
		do
			create Result.make (1, count)
		ensure -- from INDEXABLE
			not_void: Result /= void
		ensure then
			count_definition: Result.count = count
		end

	occurrences (v: like item): INTEGER is
			-- Number of times v appears.
			-- (Reference or object equality,
			-- based on object_comparison.)
		local
			pos: CURSOR
		do
			pos := cursor
			Result := sequential_occurrences (v)
			go_to (pos)
		ensure -- from BAG
			non_negative_occurrences: Result >= 0
		end
	
feature -- Status report

	after: BOOLEAN is
			-- Is there no valid position to the right of current one?
			-- (from LINEAR)
		deferred
		end

	changeable_comparison_criterion: BOOLEAN is
			-- May object_comparison be changed?
			-- (Answer: yes by default.)
			-- (from CONTAINER)
		do
			Result := True
		end

	empty: BOOLEAN is
		obsolete "ELKS 2000: Use `is_empty' instead"
			-- Is there no element?
			-- (from CONTAINER)
		do
			Result := is_empty
		end

	exhausted: BOOLEAN is
			-- Has structure been completely explored?
			-- (from LINEAR)
		do
			Result := off
		ensure -- from LINEAR
			exhausted_when_off: off implies Result
		end

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

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

	is_empty: BOOLEAN is
			-- Is structure empty?
			-- (from FINITE)
		do
			Result := (count = 0)
		end

	is_inserted (v: G): BOOLEAN is
			-- 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)
		do
			Result := has (v)
		end

	isfirst: BOOLEAN is
			-- Is cursor at first position?
		do
			Result := not is_empty and (index = 1)
		ensure
			valid_position: Result implies not is_empty
		end

	islast: BOOLEAN is
			-- Is cursor at last position?
		do
			Result := not is_empty and (index = count)
		ensure
			valid_position: Result implies not is_empty
		end

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

	off: BOOLEAN is
			-- Is there no current item?
		do
			Result := (index = 0) or (index = count + 1)
		end

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

	readable: BOOLEAN is
			-- Is there a current item that may be read?
			-- (from SEQUENCE)
		do
			Result := not off
		end

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

	valid_cursor_index (i: INTEGER): BOOLEAN is
			-- Is i correctly bounded for cursor movement?
		do
			Result := (i >= 0) and (i <= count + 1)
		ensure
			valid_cursor_index_definition: Result = ((i >= 0) and (i <= count + 1))
		end

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

	writable: BOOLEAN is
			-- Is there a current item that may be modified?
			-- (from SEQUENCE)
		do
			Result := not off
		end
	
feature -- Status setting

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

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

	back is
			-- Move to previous position.
			-- (from BILINEAR)
		require -- from BILINEAR
			not_before: not before
		deferred
		end

	before: BOOLEAN is
			-- Is there no valid position to the left of current one?
			-- (from BILINEAR)
		deferred
		end

	finish is
			-- Move cursor to last position.
			-- (No effect if empty)
		do
			if not is_empty then
				go_i_th (count)
			end
		ensure then
			at_last: not is_empty implies islast
		end

	forth is
			-- Move to next position; if no next position,
			-- ensure that exhausted will be true.
			-- (from LINEAR)
		require -- from LINEAR
			not_after: not after
		deferred
		end

	go_i_th (i: INTEGER) is
			-- Move cursor to i-th position.
		require
			valid_cursor_index: valid_cursor_index (i)
		do
			move (i - index)
		ensure
			position_expected: index = i
		end

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

	move (i: INTEGER) is
			-- Move cursor i positions. The cursor
			-- may end up off if the absolute value of i
			-- is too big.
		local
			counter, pos, final: INTEGER
		do
			if i > 0 then
				from
				until
					(counter = i) or else off
				loop
					forth
					counter := counter + 1
				end
			elseif i < 0 then
				final := index + i;
				if final <= 0 then
					start;
					back
				else
					from
						start
						pos := 1
					until
						pos = final
					loop
						forth
						pos := pos + 1
					end
				end
			end
		ensure
			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)
		end

	search (v: like item) is
			-- 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)
		do
			if before and not is_empty then
				forth
			end
			sequential_search (v)
		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
		end

	start is
			-- Move cursor to first position.
			-- (No effect if empty)
		do
			if not is_empty then
				go_i_th (1)
			end
		ensure then
			at_first: not is_empty implies isfirst
		end
	
feature -- Element change

	append (s: SEQUENCE [G]) is
			-- Append a copy of s.
			-- (from SEQUENCE)
		require -- from SEQUENCE
			argument_not_void: s /= void
		local
			l: like s
		do
			if s = Current then
				l := deep_clone (s)
			else
				l := s
			end
			from
				l.start
			until
				l.exhausted
			loop
				extend (l.item)
				l.forth
			end
		ensure -- from SEQUENCE
			new_count: count >= old count
		end

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

	fill (other: CONTAINER [G]) is
			-- 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
		local
			lin_rep: LINEAR [G]
		do
			lin_rep := other.linear_representation
			from
				lin_rep.start
			until
				not extendible or else lin_rep.off
			loop
				extend (lin_rep.item)
				lin_rep.forth
			end
		end

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

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

	put_i_th (v: like item; i: INTEGER) is
			-- Put v at i-th position.
		require -- from TABLE
			valid_key: valid_index (k)
		local
			pos: CURSOR
		do
			pos := cursor
			go_i_th (i)
			replace (v)
			go_to (pos)
		ensure then -- from INDEXABLE
			insertion_done: i_th (k) = v
		end

	replace (v: G) is
			-- Replace current item by v.
			-- (from ACTIVE)
		require -- from ACTIVE
			writable: writable
		deferred
		ensure -- from ACTIVE
			item_replaced: item = v
		end
	
feature {NONE} -- Element change

	sequence_put (v: like item) is
			-- Add v to end.
			-- (from SEQUENCE)
		require -- from COLLECTION
			extendible: extendible
		do
			extend (v)
		ensure -- from COLLECTION
			item_inserted: is_inserted (v)
		ensure then -- from SEQUENCE
			new_count: count = old count + 1
		end
	
feature -- Removal

	prune (v: like item) is
			-- Remove the first occurrence of v if any.
			-- If no such occurrence go off.
			-- (from SEQUENCE)
		require -- from COLLECTION
			prunable: prunable
		do
			start
			search (v)
			if not exhausted then
				remove
			end
		end

	prune_all (v: like item) is
			-- Remove all occurrences of v; go off.
			-- (from SEQUENCE)
		require -- from COLLECTION
			prunable
		do
			from
				start
			until
				exhausted
			loop
				search (v)
				if not exhausted then
					remove
				end
			end
		ensure -- from COLLECTION
			no_more_occurrences: not has (v)
		end

	wipe_out is
			-- Remove all items.
			-- (from COLLECTION)
		require -- from COLLECTION
			prunable
		deferred
		ensure -- from COLLECTION
			wiped_out: is_empty
		end
	
feature -- Transformation

	swap (i: INTEGER) is
			-- Exchange item at i-th position with item
			-- at cursor position.
		require
			not_off: not off
			valid_index: valid_index (i)
		local
			old_item, new_item: like item
			pos: CURSOR
		do
			pos := cursor
			old_item := item
			go_i_th (i)
			new_item := item
			replace (old_item)
			go_to (pos)
			replace (new_item)
		ensure
			swapped_to_item: item = old i_th (i)
			swapped_from_item: i_th (i) = old item
		end
	
feature -- Conversion

	linear_representation: LINEAR [G] is
			-- Representation as a linear structure
			-- (from LINEAR)
		do
			Result := Current
		end
	
feature -- Duplication

	duplicate (n: INTEGER): like Current is
			-- 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.
		require
			not_off_unless_after: off implies after
			valid_subchain: n >= 0
		deferred
		end
	
feature {NONE} -- Inapplicable

	bag_put (v: G) is
			-- (from TABLE)
		require -- from COLLECTION
			extendible: extendible
		do
		ensure -- from COLLECTION
			item_inserted: is_inserted (v)
		end

	remove is
			-- Remove current item.
		require -- from ACTIVE
			prunable: prunable
			writable: writable
		do
		end
	
feature -- Iteration

	do_all (action: PROCEDURE [ANY, TUPLE [G]]) is
			-- 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
		local
			t: TUPLE [G]
		do
			create t.make
			from
				start
			until
				after
			loop
				t.put (item, 1)
				action.call (t)
				forth
			end
		end

	do_if (action: PROCEDURE [ANY, TUPLE [G]]; test: FUNCTION [ANY, TUPLE [G], BOOLEAN]) is
			-- 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
		local
			t: TUPLE [G]
		do
			create t.make
			from
				start
			until
				after
			loop
				t.put (item, 1)
				if test.item (t) then
					action.call (t)
				end
				forth
			end
		end

	for_all (test: FUNCTION [ANY, TUPLE [G], BOOLEAN]): BOOLEAN is
			-- Is test true for all items?
			-- (from LINEAR)
		require -- from TRAVERSABLE
			test_exits: test /= void
		local
			cs: CURSOR_STRUCTURE [G]
			c: CURSOR
			t: TUPLE [G]
		do
			create t.make
			cs ?= Current
			if cs /= void then
				c := cs.cursor
			end
			from
				start
				Result := True
			until
				after or not Result
			loop
				t.put (item, 1)
				Result := test.item (t)
				forth
			end
			if cs /= void then
				cs.go_to (c)
			end
		end

	there_exists (test: FUNCTION [ANY, TUPLE [G], BOOLEAN]): BOOLEAN is
			-- Is test true for at least one item?
			-- (from LINEAR)
		require -- from TRAVERSABLE
			test_exits: test /= void
		local
			cs: CURSOR_STRUCTURE [G]
			c: CURSOR
			t: TUPLE [G]
		do
			create t.make
			cs ?= Current
			if cs /= void then
				c := cs.cursor
			end
			from
				start
			until
				after or Result
			loop
				t.put (item, 1)
				Result := test.item (t)
				forth
			end
			if cs /= void then
				cs.go_to (c)
			end
		end
	
invariant

	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 ANY
	reflexive_equality: standard_is_equal (Current)
	reflexive_conformance: conforms_to (Current)
		-- 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 CHAIN


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