note
	description: "[
		Objects that are able to iterate over two-way chains,
		on which they can perform repeated actions and tests according
		to a number of predefined control structures such as if,
		until and others.
	]"
	library: "Free implementation of ELKS library"
	legal: "See notice at end of class."
	status: "See notice at end of class."
	names: iterators, iteration, two_way_chain_iterators, two_way_chain_iteration
	traversal: sequential
	exploration: forward, backward
	date: "$Date: 2017-04-10 07:37:21 +0000 (Mon, 10 Apr 2017) $"
	revision: "$Revision: 100119 $"

class 
	TWO_WAY_CHAIN_ITERATOR [G]

create 
	set

feature -- Initialization

	set (s: like target)
			-- Make s the new target of iterations.
			-- (from LINEAR_ITERATOR)
		require -- from ITERATOR
			target_exists: s /= Void
		do
			target := s
		ensure -- from ITERATOR
				target = s
				target /= Void
		end
	
feature {NONE} -- Initialization

	default_create
			-- Process instances of classes with no creation clause.
			-- (Default: do nothing.)
			-- (from ANY)
		do
		end
	
feature -- Access

	generating_type: TYPE [detachable TWO_WAY_CHAIN_ITERATOR [G]]
			-- Type of current object
			-- (type of which it is a direct instance)
			-- (from ANY)
		external
			"built_in"
		ensure -- from ANY
			generating_type_not_void: Result /= Void
		end

	generator: STRING_8
			-- Name of current object's generating class
			-- (base class of the type of which it is a direct instance)
			-- (from ANY)
		external
			"built_in"
		ensure -- from ANY
			generator_not_void: Result /= Void
			generator_not_empty: not Result.is_empty
		end

	item: G
			-- The item at cursor position in target
			-- (from LINEAR_ITERATOR)
		require -- from LINEAR_ITERATOR
			not_off: not target.off
		do
			Result := target.item
		end

	item_tuple: TUPLE [G]
			-- Tuple containing a single element,
			-- the item at cursor position in target''
			-- (from LINEAR_ITERATOR)
		require -- from LINEAR_ITERATOR
			not_off: not target.off
		do
			Result := [target.item]
		ensure -- from LINEAR_ITERATOR
			item_tuple_attached: Result /= Void
		end

	target: CHAIN [G]
			-- The structure to which iteration features will apply.
	
feature -- Comparison

	frozen deep_equal (a: detachable ANY; b: like arg #1): BOOLEAN
			-- Are a and b either both void
			-- or attached to isomorphic object structures?
			-- (from ANY)
		do
			if a = Void then
				Result := b = Void
			else
				Result := b /= Void and then a.is_deep_equal (b)
			end
		ensure -- from ANY
			instance_free: class
			shallow_implies_deep: standard_equal (a, b) implies Result
			both_or_none_void: (a = Void) implies (Result = (b = Void))
			same_type: (Result and (a /= Void)) implies (b /= Void and then a.same_type (b))
			symmetric: Result implies deep_equal (b, a)
		end

	frozen equal (a: detachable ANY; b: like arg #1): BOOLEAN
			-- Are a and b either both void or attached
			-- to objects considered equal?
			-- (from ANY)
		do
			if a = Void then
				Result := b = Void
			else
				Result := b /= Void and then a.is_equal (b)
			end
		ensure -- from ANY
			instance_free: class
			definition: Result = (a = Void and b = Void) or else ((a /= Void and b /= Void) and then a.is_equal (b))
		end

	frozen is_deep_equal alias "≡≡≡" (other: TWO_WAY_CHAIN_ITERATOR [G]): BOOLEAN
			-- Are Current and other attached to isomorphic object structures?
			-- (from ANY)
		require -- from ANY
			other_not_void: other /= Void
		external
			"built_in"
		ensure -- from ANY
			shallow_implies_deep: standard_is_equal (other) implies Result
			same_type: Result implies same_type (other)
			symmetric: Result implies other.is_deep_equal (Current)
		end

	is_equal (other: TWO_WAY_CHAIN_ITERATOR [G]): BOOLEAN
			-- Is other attached to an object considered
			-- equal to current object?
			-- (from ANY)
		require -- from ANY
			other_not_void: other /= Void
		external
			"built_in"
		ensure -- from ANY
			symmetric: Result implies other ~ Current
			consistent: standard_is_equal (other) implies Result
		end

	frozen standard_equal (a: detachable ANY; b: like arg #1): BOOLEAN
			-- Are a and b either both void or attached to
			-- field-by-field identical objects of the same type?
			-- Always uses default object comparison criterion.
			-- (from ANY)
		do
			if a = Void then
				Result := b = Void
			else
				Result := b /= Void and then a.standard_is_equal (b)
			end
		ensure -- from ANY
			instance_free: class
			definition: Result = (a = Void and b = Void) or else ((a /= Void and b /= Void) and then a.standard_is_equal (b))
		end

	frozen standard_is_equal alias "≜" (other: TWO_WAY_CHAIN_ITERATOR [G]): BOOLEAN
			-- Is other attached to an object of the same type
			-- as current object, and field-by-field identical to it?
			-- (from ANY)
		require -- from ANY
			other_not_void: other /= Void
		external
			"built_in"
		ensure -- from ANY
			same_type: Result implies same_type (other)
			symmetric: Result implies other.standard_is_equal (Current)
		end
	
feature -- Status report

	conforms_to (other: ANY): BOOLEAN
			-- Does type of current object conform to type
			-- of other (as per Eiffel: The Language, chapter 13)?
			-- (from ANY)
		require -- from ANY
			other_not_void: other /= Void
		external
			"built_in"
		end

	invariant_value: BOOLEAN
			-- Is the invariant satisfied?
			-- (Redefinitions of this feature will usually involve
			-- target; if so, make sure that the result is defined
			-- when target = Void.)
			-- (from ITERATOR)
		do
			Result := True
		end

	same_type (other: ANY): BOOLEAN
			-- Is type of current object identical to type of other?
			-- (from ANY)
		require -- from ANY
			other_not_void: other /= Void
		external
			"built_in"
		ensure -- from ANY
			definition: Result = (conforms_to (other) and other.conforms_to (Current))
		end
	
feature -- Cursor movement

	back
			-- Move cursor of target backward one position.
		do
			target.back
		end

	exhausted: BOOLEAN
			-- Is target exhausted?
			-- (from LINEAR_ITERATOR)
		do
			Result := target.exhausted
		end

	finish
			-- Move cursor of target to last position.
		do
			target.finish
		end

	forth
			-- Move to next position of target.
			-- (from LINEAR_ITERATOR)
		do
			target.forth
		end

	off: BOOLEAN
			-- Is position of target off?
			-- (from LINEAR_ITERATOR)
		do
			Result := target.off
		end

	start
			-- Move to first position of target.
			-- (from LINEAR_ITERATOR)
		do
			target.start
		end
	
feature -- Duplication

	frozen clone (other: detachable ANY): like other
		obsolete "Use `twin' instead. [2017-05-31]"
			-- Void if other is void; otherwise new object
			-- equal to other
			--
			-- For non-void other, clone calls copy;
			-- to change copying/cloning semantics, redefine copy.
			-- (from ANY)
		do
			if other /= Void then
				Result := other.twin
			end
		ensure -- from ANY
			instance_free: class
			equal: Result ~ other
		end

	copy (other: TWO_WAY_CHAIN_ITERATOR [G])
			-- Update current object using fields of object attached
			-- to other, so as to yield equal objects.
			-- (from ANY)
		require -- from ANY
			other_not_void: other /= Void
			type_identity: same_type (other)
		external
			"built_in"
		ensure -- from ANY
			is_equal: Current ~ other
		end

	frozen deep_clone (other: detachable ANY): like other
		obsolete "Use `deep_twin' instead. [2017-05-31]"
			-- Void if other is void: otherwise, new object structure
			-- recursively duplicated from the one attached to other
			-- (from ANY)
		do
			if other /= Void then
				Result := other.deep_twin
			end
		ensure -- from ANY
			instance_free: class
			deep_equal: deep_equal (other, Result)
		end

	frozen deep_copy (other: TWO_WAY_CHAIN_ITERATOR [G])
			-- Effect equivalent to that of:
			--		copy (other . deep_twin)
			-- (from ANY)
		require -- from ANY
			other_not_void: other /= Void
		do
			copy (other.deep_twin)
		ensure -- from ANY
			deep_equal: deep_equal (Current, other)
		end

	frozen deep_twin: TWO_WAY_CHAIN_ITERATOR [G]
			-- New object structure recursively duplicated from Current.
			-- (from ANY)
		external
			"built_in"
		ensure -- from ANY
			deep_twin_not_void: Result /= Void
			deep_equal: deep_equal (Current, Result)
		end

	frozen standard_clone (other: detachable ANY): like other
		obsolete "Use `standard_twin' instead. [2017-05-31]"
			-- Void if other is void; otherwise new object
			-- field-by-field identical to other.
			-- Always uses default copying semantics.
			-- (from ANY)
		do
			if other /= Void then
				Result := other.standard_twin
			end
		ensure -- from ANY
			instance_free: class
			equal: standard_equal (Result, other)
		end

	frozen standard_copy (other: TWO_WAY_CHAIN_ITERATOR [G])
			-- Copy every field of other onto corresponding field
			-- of current object.
			-- (from ANY)
		require -- from ANY
			other_not_void: other /= Void
			type_identity: same_type (other)
		external
			"built_in"
		ensure -- from ANY
			is_standard_equal: standard_is_equal (other)
		end

	frozen standard_twin: TWO_WAY_CHAIN_ITERATOR [G]
			-- New object field-by-field identical to other.
			-- Always uses default copying semantics.
			-- (from ANY)
		external
			"built_in"
		ensure -- from ANY
			standard_twin_not_void: Result /= Void
			equal: standard_equal (Result, Current)
		end

	frozen twin: TWO_WAY_CHAIN_ITERATOR [G]
			-- New object equal to Current
			-- twin calls copy; to change copying/twinning semantics, redefine copy.
			-- (from ANY)
		external
			"built_in"
		ensure -- from ANY
			twin_not_void: Result /= Void
			is_equal: Result ~ Current
		end
	
feature -- Basic operations

	frozen as_attached: attached TWO_WAY_CHAIN_ITERATOR [G]
		obsolete "Remove calls to this feature. [2017-05-31]"
			-- Attached version of Current.
			-- (Can be used during transitional period to convert
			-- non-void-safe classes to void-safe ones.)
			-- (from ANY)
		do
			Result := Current
		end

	frozen default: detachable TWO_WAY_CHAIN_ITERATOR [G]
			-- Default value of object's type
			-- (from ANY)
		do
		end

	frozen default_pointer: POINTER
			-- Default value of type POINTER
			-- (Avoid the need to write p.default for
			-- some p of type POINTER.)
			-- (from ANY)
		do
		ensure -- from ANY
			instance_free: class
		end

	default_rescue
			-- Process exception for routines with no Rescue clause.
			-- (Default: do nothing.)
			-- (from ANY)
		do
		end

	frozen do_nothing
			-- Execute a null action.
			-- (from ANY)
		do
		ensure -- from ANY
			instance_free: class
		end
	
feature -- Iteration

	continue_for_back (action: PROCEDURE [G]; n, k: INTEGER_32)
			-- Apply action to every k-th item,
			-- n times if possible.
			-- (from LINEAR_ITERATOR)
		require -- from LINEAR_ITERATOR
			valid_repetition: n >= 0
			valid_skip: k >= 1
		local
			i, j: INTEGER_32
		do
			from
			invariant
					i >= 0 and i <= n
			variant
					n - i
			until
				exhausted or else i = n
			loop
				action.call ([target.item])
				i := i + 1
				from
					j := 0
				invariant
						j >= 0 and j <= k
				variant
						k - j
				until
					exhausted or else j = k
				loop
					forth
					j := j + 1
				end
			end
		end

	continue_for (action: PROCEDURE [G]; n, k: INTEGER_32)
			-- Apply action to every k-th item,
			-- n times if possible.
			-- (from LINEAR_ITERATOR)
		require -- from LINEAR_ITERATOR
			valid_repetition: n >= 0
			valid_skip: k >= 1
		local
			i, j: INTEGER_32
		do
			from
			invariant
					i >= 0 and i <= n
			variant
					n - i
			until
				exhausted or else i = n
			loop
				action.call ([target.item])
				i := i + 1
				from
					j := 0
				invariant
						j >= 0 and j <= k
				variant
						k - j
				until
					exhausted or else j = k
				loop
					forth
					j := j + 1
				end
			end
		end

	continue_search (test: FUNCTION [G, BOOLEAN]; b: BOOLEAN)
			-- Search the first item of target
			-- satisfying: test equals to b
			-- (from the current position of target).
			-- (from LINEAR_ITERATOR)
		do
			from
			invariant
					invariant_value
			until
				exhausted or else (b = test.item ([target.item]))
			loop
				forth
			end
		ensure then -- from LINEAR_ITERATOR
			found: not exhausted = (b = test.item ([target.item]))
		end

	continue_search_back (test: FUNCTION [G, BOOLEAN]; b: BOOLEAN)
			-- Search the first item of target
			-- satisfying: test equals to b
			-- (from the current position of target).
			-- (from LINEAR_ITERATOR)
		do
			from
			invariant
					invariant_value
			until
				exhausted or else (b = test.item ([target.item]))
			loop
				forth
			end
		ensure then -- from LINEAR_ITERATOR
			found: not exhausted = (b = test.item ([target.item]))
		end

	continue_until_back (action: PROCEDURE [G]; test: FUNCTION [G, BOOLEAN])
			-- Apply action to every item of target up to
			-- and including first one satisfying test.
			-- (from the current position of target).
			-- (from LINEAR_ITERATOR)
		require -- from LINEAR_ITERATOR
			invariant_satisfied: invariant_value
		do
			from
				if not exhausted then
					action.call ([target.item])
				end
			invariant
					invariant_value
			until
				exhausted or else test.item ([target.item])
			loop
				forth
				if not exhausted then
					action.call ([target.item])
				end
			end
		ensure then -- from LINEAR_ITERATOR
			achieved: not exhausted implies test.item ([target.item])
		end

	continue_until (action: PROCEDURE [G]; test: FUNCTION [G, BOOLEAN])
			-- Apply action to every item of target up to
			-- and including first one satisfying test.
			-- (from the current position of target).
			-- (from LINEAR_ITERATOR)
		require -- from LINEAR_ITERATOR
			invariant_satisfied: invariant_value
		do
			from
				if not exhausted then
					action.call ([target.item])
				end
			invariant
					invariant_value
			until
				exhausted or else test.item ([target.item])
			loop
				forth
				if not exhausted then
					action.call ([target.item])
				end
			end
		ensure then -- from LINEAR_ITERATOR
			achieved: not exhausted implies test.item ([target.item])
		end

	continue_while (action: PROCEDURE [G]; test: FUNCTION [G, BOOLEAN])
			-- Apply action to every item of target up to
			-- and including first one not satisfying test
			-- (from the current position of target).
			-- (from LINEAR_ITERATOR)
		require else -- from LINEAR_ITERATOR
			invariant_satisfied: invariant_value
		do
			from
				if not exhausted then
					action.call ([target.item])
				end
			invariant
					invariant_value
			until
				exhausted or else not test.item ([target.item])
			loop
				forth
				if not exhausted then
					action.call ([target.item])
				end
			end
		ensure then -- from LINEAR_ITERATOR
			finished: not exhausted implies not test.item ([target.item])
		end

	continue_while_back (action: PROCEDURE [G]; test: FUNCTION [G, BOOLEAN])
			-- Apply action to every item of target up to
			-- and including first one not satisfying test
			-- (from the current position of target).
			-- (from LINEAR_ITERATOR)
		require else -- from LINEAR_ITERATOR
			invariant_satisfied: invariant_value
		do
			from
				if not exhausted then
					action.call ([target.item])
				end
			invariant
					invariant_value
			until
				exhausted or else not test.item ([target.item])
			loop
				forth
				if not exhausted then
					action.call ([target.item])
				end
			end
		ensure then -- from LINEAR_ITERATOR
			finished: not exhausted implies not test.item ([target.item])
		end

	do_all (action: PROCEDURE [G])
			-- Apply action to every item of target.
			-- (from ITERATOR)
		require -- from ITERATOR
			action_exists: action /= Void
		do
			target.do_all (action)
		end

	do_all_back (action: PROCEDURE [G])
			-- Apply action to every item of target.
			-- (from ITERATOR)
		require -- from ITERATOR
			action_exists: action /= Void
		do
			target.do_all (action)
		end

	do_for_back (action: PROCEDURE [G]; i, n, k: INTEGER_32)
			-- Apply action to every k-th item,
			-- n times if possible, starting from i-th.
			-- (from LINEAR_ITERATOR)
		require -- from LINEAR_ITERATOR
			valid_start: i >= 1
			valid_repetition: n >= 0
			valid_skip: k >= 1
		local
			j: INTEGER_32
		do
			from
				start
				j := 1
			invariant
					j >= 1 and j <= i
			variant
					i - j
			until
				exhausted or else j = i
			loop
				forth
				j := j + 1
			end
			continue_for (action, n, k)
		end

	do_for (action: PROCEDURE [G]; i, n, k: INTEGER_32)
			-- Apply action to every k-th item,
			-- n times if possible, starting from i-th.
			-- (from LINEAR_ITERATOR)
		require -- from LINEAR_ITERATOR
			valid_start: i >= 1
			valid_repetition: n >= 0
			valid_skip: k >= 1
		local
			j: INTEGER_32
		do
			from
				start
				j := 1
			invariant
					j >= 1 and j <= i
			variant
					i - j
			until
				exhausted or else j = i
			loop
				forth
				j := j + 1
			end
			continue_for (action, n, k)
		end

	do_if (action: PROCEDURE [G]; test: FUNCTION [G, BOOLEAN])
			-- Apply action to every item of target satisfying test.
			-- (from ITERATOR)
		require -- from ITERATOR
			action_exists: action /= Void
			test_exists: test /= Void
		do
			target.do_if (action, test)
		end

	do_if_back (action: PROCEDURE [G]; test: FUNCTION [G, BOOLEAN])
			-- Apply action to every item of target satisfying test.
			-- (from ITERATOR)
		require -- from ITERATOR
			action_exists: action /= Void
			test_exists: test /= Void
		do
			target.do_if (action, test)
		end

	do_until_back (action: PROCEDURE [G]; test: FUNCTION [G, BOOLEAN])
			-- Apply action to every item of target up to
			-- and including first one satisfying test.
			-- (from LINEAR_ITERATOR)
		require -- from ITERATOR
			action_exists: action /= Void
			test_exists: test /= Void
		do
			start
			continue_until (action, test)
		ensure then -- from LINEAR_ITERATOR
			achieved: not exhausted implies test.item ([target.item])
		end

	do_until (action: PROCEDURE [G]; test: FUNCTION [G, BOOLEAN])
			-- Apply action to every item of target up to
			-- and including first one satisfying test.
			-- (from LINEAR_ITERATOR)
		require -- from ITERATOR
			action_exists: action /= Void
			test_exists: test /= Void
		do
			start
			continue_until (action, test)
		ensure then -- from LINEAR_ITERATOR
			achieved: not exhausted implies test.item ([target.item])
		end

	do_while (action: PROCEDURE [G]; test: FUNCTION [G, BOOLEAN])
			-- Apply action to every item of target up to
			-- and including first one not satisfying test.
			-- (from the start of target)
			-- (from LINEAR_ITERATOR)
		require -- from ITERATOR
			action_exists: action /= Void
			test_exists: test /= Void
		do
			start
			continue_while (action, test)
		ensure then -- from LINEAR_ITERATOR
			finished: not exhausted implies not test.item ([target.item])
		end

	do_while_back (action: PROCEDURE [G]; test: FUNCTION [G, BOOLEAN])
			-- Apply action to every item of target up to
			-- and including first one not satisfying test.
			-- (from the start of target)
			-- (from LINEAR_ITERATOR)
		require -- from ITERATOR
			action_exists: action /= Void
			test_exists: test /= Void
		do
			start
			continue_while (action, test)
		ensure then -- from LINEAR_ITERATOR
			finished: not exhausted implies not test.item ([target.item])
		end

	for_all (test: FUNCTION [G, BOOLEAN]): BOOLEAN
			-- Does test return true for
			-- all items of target?
			-- (from LINEAR_ITERATOR)
		require -- from ITERATOR
			test_exists: test /= Void
		do
			search (test, False)
			Result := exhausted
		end

	for_all_back (test: FUNCTION [G, BOOLEAN]): BOOLEAN
			-- Does test return true for
			-- all items of target?
			-- (from LINEAR_ITERATOR)
		require -- from ITERATOR
			test_exists: test /= Void
		do
			search (test, False)
			Result := exhausted
		end

	search (test: FUNCTION [G, BOOLEAN]; b: BOOLEAN)
			-- Search the first item of target for which test
			-- has the same value as b (both true or both false).
			-- (from LINEAR_ITERATOR)
		do
			start
			continue_search (test, b)
		end

	search_back (test: FUNCTION [G, BOOLEAN]; b: BOOLEAN)
			-- Search the first item of target for which test
			-- has the same value as b (both true or both false).
			-- (from LINEAR_ITERATOR)
		do
			start
			continue_search (test, b)
		end

	there_exists (test: FUNCTION [G, BOOLEAN]): BOOLEAN
			-- Does test return true for
			-- at least one item of target?
			-- (from LINEAR_ITERATOR)
		require -- from ITERATOR
			test_exists: test /= Void
		do
			search (test, True)
			Result := not exhausted
		end

	there_exists_back (test: FUNCTION [G, BOOLEAN]): BOOLEAN
			-- Does test return true for
			-- at least one item of target?
			-- (from LINEAR_ITERATOR)
		require -- from ITERATOR
			test_exists: test /= Void
		do
			search (test, True)
			Result := not exhausted
		end

	until_continue (action: PROCEDURE [G]; test: FUNCTION [G, BOOLEAN])
			-- Apply action to every item of target from current
			-- position, up to but excluding first one satisfying test.
			-- (from LINEAR_ITERATOR)
		require -- from LINEAR_ITERATOR
			invariant_satisfied: invariant_value
		do
			from
			invariant
					invariant_value
			until
				exhausted or else test.item ([target.item])
			loop
				action.call ([item])
				forth
			end
		ensure -- from LINEAR_ITERATOR
			achieved: exhausted or else test.item ([target.item])
			invariant_satisfied: invariant_value
		end

	until_continue_back (action: PROCEDURE [G]; test: FUNCTION [G, BOOLEAN])
			-- Apply action to every item of target from current
			-- position, up to but excluding first one satisfying test.
			-- (from LINEAR_ITERATOR)
		require -- from LINEAR_ITERATOR
			invariant_satisfied: invariant_value
		do
			from
			invariant
					invariant_value
			until
				exhausted or else test.item ([target.item])
			loop
				action.call ([item])
				forth
			end
		ensure -- from LINEAR_ITERATOR
			achieved: exhausted or else test.item ([target.item])
			invariant_satisfied: invariant_value
		end

	until_do_back (action: PROCEDURE [G]; test: FUNCTION [G, BOOLEAN])
			-- Apply action to every item of target up to
			-- but excluding first one satisfying test.
			-- (Apply to full list if no item satisfies test.)
			-- (from LINEAR_ITERATOR)
		require -- from ITERATOR
			action_exists: action /= Void
			test_exists: test /= Void
		do
			start
			until_continue (action, test)
		ensure then -- from LINEAR_ITERATOR
			achieved: not exhausted implies test.item ([target.item])
		end

	until_do (action: PROCEDURE [G]; test: FUNCTION [G, BOOLEAN])
			-- Apply action to every item of target up to
			-- but excluding first one satisfying test.
			-- (Apply to full list if no item satisfies test.)
			-- (from LINEAR_ITERATOR)
		require -- from ITERATOR
			action_exists: action /= Void
			test_exists: test /= Void
		do
			start
			until_continue (action, test)
		ensure then -- from LINEAR_ITERATOR
			achieved: not exhausted implies test.item ([target.item])
		end

	while_continue (action: PROCEDURE [G]; test: FUNCTION [G, BOOLEAN])
			-- Apply action to every item of target up to
			-- but excluding first one not satisfying test.
			-- (from LINEAR_ITERATOR)
		do
			from
			invariant
					invariant_value
			until
				exhausted or else not test.item ([target.item])
			loop
				action.call ([target.item])
				forth
			end
		ensure -- from LINEAR_ITERATOR
			finished: not exhausted implies not test.item ([target.item])
		end

	while_continue_back (action: PROCEDURE [G]; test: FUNCTION [G, BOOLEAN])
			-- Apply action to every item of target up to
			-- but excluding first one not satisfying test.
			-- (from LINEAR_ITERATOR)
		do
			from
			invariant
					invariant_value
			until
				exhausted or else not test.item ([target.item])
			loop
				action.call ([target.item])
				forth
			end
		ensure -- from LINEAR_ITERATOR
			finished: not exhausted implies not test.item ([target.item])
		end

	while_do_back (action: PROCEDURE [G]; test: FUNCTION [G, BOOLEAN])
			-- Apply action to every item of target up to
			-- but excluding first one not satisfying test.
			-- (Apply to full list if all items satisfy test.)
			-- (from LINEAR_ITERATOR)
		require -- from ITERATOR
			action_exists: action /= Void
			test_exists: test /= Void
		do
			start
			while_continue (action, test)
		ensure then -- from LINEAR_ITERATOR
			finished: not exhausted implies not test.item ([target.item])
		end

	while_do (action: PROCEDURE [G]; test: FUNCTION [G, BOOLEAN])
			-- Apply action to every item of target up to
			-- but excluding first one not satisfying test.
			-- (Apply to full list if all items satisfy test.)
			-- (from LINEAR_ITERATOR)
		require -- from ITERATOR
			action_exists: action /= Void
			test_exists: test /= Void
		do
			start
			while_continue (action, test)
		ensure then -- from LINEAR_ITERATOR
			finished: not exhausted implies not test.item ([target.item])
		end
	
feature -- Output

	Io: STD_FILES
			-- Handle to standard file setup
			-- (from ANY)
		once
			create Result;
			Result.set_output_default
		ensure -- from ANY
			instance_free: class
			io_not_void: Result /= Void
		end

	out: STRING_8
			-- New string containing terse printable representation
			-- of current object
			-- (from ANY)
		do
			Result := tagged_out
		ensure -- from ANY
			out_not_void: Result /= Void
		end

	print (o: detachable ANY)
			-- Write terse external representation of o
			-- on standard output.
			-- (from ANY)
		local
			s: READABLE_STRING_8
		do
			if attached o then
				s := o.out
				if attached {READABLE_STRING_32} s as s32 then
					Io.put_string_32 (s32)
				elseif attached {READABLE_STRING_8} s as s8 then
					Io.put_string (s8)
				else
					Io.put_string_32 (s.as_string_32)
				end
			end
		ensure -- from ANY
			instance_free: class
		end

	frozen tagged_out: STRING_8
			-- New string containing terse printable representation
			-- of current object
			-- (from ANY)
		external
			"built_in"
		ensure -- from ANY
			tagged_out_not_void: Result /= Void
		end
	
feature -- Platform

	Operating_environment: OPERATING_ENVIRONMENT
			-- Objects available from the operating system
			-- (from ANY)
		once
			create Result
		ensure -- from ANY
			instance_free: class
			operating_environment_not_void: Result /= Void
		end
	
feature {NONE} -- Retrieval

	frozen internal_correct_mismatch
			-- Called from runtime to perform a proper dynamic dispatch on correct_mismatch
			-- from MISMATCH_CORRECTOR.
			-- (from ANY)
		local
			l_msg: STRING_32
			l_exc: EXCEPTIONS
		do
			if attached {MISMATCH_CORRECTOR} Current as l_corrector then
				l_corrector.correct_mismatch
			else
				create l_msg.make_from_string ("Mismatch: ".as_string_32)
				create l_exc;
				l_msg.append (generating_type.name_32);
				l_exc.raise_retrieval_exception (l_msg)
			end
		end
	
invariant
		-- from LINEAR_ITERATOR
	target_exists: target /= Void

		-- from ITERATOR
	traversable_exists: target /= Void

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

note
	copyright: "Copyright (c) 1984-2012, Eiffel Software and others"
	license: "Eiffel Forum License v2 (see http://www.eiffel.com/licensing/forum.txt)"
	source: "[
		Eiffel Software
		5949 Hollister Ave., Goleta, CA 93117 USA
		Telephone 805-685-1006, Fax 805-685-6869
		Website http://www.eiffel.com
		Customer support http://support.eiffel.com
	]"

end -- class TWO_WAY_CHAIN_ITERATOR

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