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	description: "Objects that are able to iterate over linear structures"
	status: "See notice at end of class"
	names: iterators, iteration, linear_iterators, linear_iteration
	date: "$Date: 2001-11-16 20:32:23 +0000 (Fri, 16 Nov 2001) $"
	revision: "$Revision: 51435 $"

class 
	LINEAR_ITERATOR [G]

create 
	set

feature -- Initialization

	set (s: like target) is
			-- Make s the new target of iterations.
		require -- from ITERATOR
			target_exists: s /= void
		do
			Precursor  (s)
			create internal_item_tuple.make
		ensure -- from ITERATOR
			target = s
			target /= void
		end
	
feature -- Access

	item: G is
			-- The item at cursor position in target
		require
			traversable_exists: target /= void
		do
			Result := target.item
		end

	item_tuple: TUPLE [G] is
			-- Tuple containing a single element,
			-- the item at cursor position in target''
		do
			internal_item_tuple.put (target.item, 1)
			Result := internal_item_tuple
		end

	target: LINEAR [G]
			-- The structure to which iteration features will apply.
	
feature -- Status report

	invariant_value: BOOLEAN is
			-- 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
	
feature -- Cursor movement

	exhausted: BOOLEAN is
			-- Is target exhausted?
		do
			Result := target.exhausted
		end

	forth is
			-- Move to next position of target.
		do
			target.forth
		end

	off: BOOLEAN is
			-- Is position of target off?
		do
			Result := target.off
		end

	start is
			-- Move to first position of target.
		do
			target.start
		end
	
feature -- Implementation

	internal_item_tuple: TUPLE [G]
			-- Field holding the last item of target
	
feature -- Iteration

	continue_for (action: PROCEDURE [ANY, TUPLE [G]]; n, k: INTEGER) is
			-- Apply action to every k-th item,
			-- n times if possible.
		require
			valid_repetition: n >= 0
			valid_skip: k >= 1
		local
			i, j: INTEGER
		do
			from
			invariant
				i >= 0 and i <= n
			variant
				n - i
			until
				exhausted or else i = n
			loop
				action.call (item_tuple)
				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 [ANY, TUPLE [G], BOOLEAN]; b: BOOLEAN) is
			-- Search the first item of target
			-- satisfying: test equals to b
			-- (from the current position of target).
		do
			from
			invariant
				invariant_value
			until
				exhausted or else (b = test.item (item_tuple))
			loop
				forth
			end
		ensure then
			found: not exhausted = (b = test.item (item_tuple))
		end

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

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

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

	do_for (action: PROCEDURE [ANY, TUPLE [G]]; i, n, k: INTEGER) is
			-- Apply action to every k-th item,
			-- n times if possible, starting from i-th.
		require
			valid_start: i >= 1
			valid_repetition: n >= 0
			valid_skip: k >= 1
		local
			j: INTEGER
		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 [ANY, TUPLE [G]]; test: FUNCTION [ANY, TUPLE [G], BOOLEAN]) is
			-- 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 (action: PROCEDURE [ANY, TUPLE [G]]; test: FUNCTION [ANY, TUPLE [G], BOOLEAN]) is
			-- Apply action to every item of target up to
			-- and including first one satisfying test.
		require -- from ITERATOR
			action_exists: action /= void
			test_exists: test /= void
		do
			start
			continue_until (action, test)
		ensure then
			achieved: not exhausted implies test.item (item_tuple)
		end

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

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

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

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

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

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

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

	while_do (action: PROCEDURE [ANY, TUPLE [G]]; test: FUNCTION [ANY, TUPLE [G], BOOLEAN]) is
			-- 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.)
		require -- from ITERATOR
			action_exists: action /= void
			test_exists: test /= void
		do
			start
			while_continue (action, test)
		ensure then
			finished: not exhausted implies not test.item (item_tuple)
		end
	
invariant

	target_exists: target /= void
	item_tuple_exists: item_tuple /= void
	internal_item_tuple_exists: internal_item_tuple /= void
		-- from ANY
	reflexive_equality: standard_is_equal (Current)
	reflexive_conformance: conforms_to (Current)
		-- from ITERATOR
	traversable_exists: target /= void

end -- class LINEAR_ITERATOR


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