    indexing
    	description: "Trees, without commitment to a particular representation"
    	legal: "See notice at end of class."
    	status: "See notice at end of class."
    	names: tree
    	access: cursor, membership
    	representation: recursive
    	contents: generic
    	date: "$Date: 2006-09-15 17:28:10 -0700 (Fri, 15 Sep 2006) $"
    	revision: "$Revision: 63620 $"

    deferred class interface
    	TREE [G]

    feature -- Access

    	child: like parent
    			-- Current child node
    		require
    			readable: readable_child

    	child_cursor: CURSOR
    			-- Current cursor position

    	child_index: INTEGER_32
    			-- Index of current child
    		ensure
    			valid_index: Result >= 0 and Result <= arity + 1

    	child_item: like item
    			-- Item in current child node
    		require
    			readable: child_readable

    	first_child: like parent
    			-- Leftmost child
    		require
    			is_not_leaf: not is_leaf

    	generating_type: STRING_8
    			-- Name of current object's generating type
    			-- (type of which it is a direct instance)
    			-- (from ANY)

    	generator: STRING_8
    			-- Name of current object's generating class
    			-- (base class of the type of which it is a direct instance)
    			-- (from ANY)

    	item: G
    			-- Item in current node

    	last_child: like first_child
    			-- Right most child
    		require
    			is_not_leaf: not is_leaf

    	left_sibling: like parent
    			-- Left neighbor (if any)
    		require
    			is_not_root: not is_root
    		ensure
    			is_sibling: Result /= Void implies is_sibling (Result)
    			right_is_current: (Result /= Void) implies (Result.right_sibling = Current)

    	parent: TREE [G]
    			-- Parent of current node

    	right_sibling: like parent
    			-- Right neighbor (if any)
    		require
    			is_not_root: not is_root
    		ensure
    			is_sibling: Result /= Void implies is_sibling (Result)
    			left_is_current: (Result /= Void) implies (Result.left_sibling = Current)

    feature -- Measurement

    	arity: INTEGER_32
    			-- Number of children

    	child_capacity: INTEGER_32
    			-- Maximal number of children

    	count: INTEGER_32
    			-- Number of items

    feature -- Comparison

    	frozen deep_equal (some: ANY; other: like arg #1): BOOLEAN
    			-- Are `some' and `other' either both void
    			-- or attached to isomorphic object structures?
    			-- (from ANY)
    		ensure -- from ANY
    			shallow_implies_deep: standard_equal (some, other) implies Result
    			both_or_none_void: (some = Void) implies (Result = (other = Void))
    			same_type: (Result and (some /= Void)) implies some.same_type (other)
    			symmetric: Result implies deep_equal (other, some)

    	frozen equal (some: ANY; other: like arg #1): BOOLEAN
    			-- Are `some' and `other' either both void or attached
    			-- to objects considered equal?
    			-- (from ANY)
    		ensure -- from ANY
    			definition: Result = (some = Void and other = Void) or else ((some /= Void and other /= Void) and then some.is_equal (other))

    	is_equal (other: like Current): BOOLEAN
    			-- Does `other' contain the same elements?
    			-- (Reference or object equality,
    			-- based on object_comparison.)
    		require -- from ANY
    			other_not_void: other /= Void
    		ensure -- from ANY
    			symmetric: Result implies other.is_equal (Current)
    			consistent: standard_is_equal (other) implies Result

    	node_is_equal (other: like Current): BOOLEAN
    			-- Is `other' equal to Current?
    		require
    			other_not_void: other /= Void

    	frozen standard_equal (some: ANY; other: like arg #1): BOOLEAN
    			-- Are `some' and `other' either both void or attached to
    			-- field-by-field identical objects of the same type?
    			-- Always uses default object comparison criterion.
    			-- (from ANY)
    		ensure -- from ANY
    			definition: Result = (some = Void and other = Void) or else ((some /= Void and other /= Void) and then some.standard_is_equal (other))

    	frozen standard_is_equal (other: like Current): 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
    		ensure -- from ANY
    			same_type: Result implies same_type (other)
    			symmetric: Result implies other.standard_is_equal (Current)

    feature -- Status report

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

    	child_after: BOOLEAN
    			-- Is there no valid child position to the right of cursor?

    	child_before: BOOLEAN
    			-- Is there no valid child position to the left of cursor?

    	child_isfirst: BOOLEAN
    			-- Is cursor under first child?
    		ensure
    			not_is_leaf: Result implies not is_leaf

    	child_islast: BOOLEAN
    			-- Is cursor under last child?
    		ensure
    			not_is_leaf: Result implies not is_leaf

    	child_off: BOOLEAN
    			-- Is there no current child?

    	child_readable: BOOLEAN
    			-- Is there a current child_item to be read?

    	child_writable: BOOLEAN
    			-- Is there a current child_item that may be modified?

    	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

    	has (v: G): BOOLEAN
    			-- Does subtree include `v'?
    			-- (Reference or object equality,
    			-- based on object_comparison.)
    		ensure -- from CONTAINER
    			not_found_in_empty: Result implies not is_empty

    	is_empty: BOOLEAN
    			-- Is structure empty of items?

    	is_leaf: BOOLEAN
    			-- Are there no children?

    	is_root: BOOLEAN
    			-- Is there no parent?

    	is_sibling (other: like parent): BOOLEAN
    			-- Are current node and `other' siblings?
    		require
    			other_exists: other /= Void
    		ensure
    			not_root: Result implies not is_root
    			other_not_root: Result implies not other.is_root
    			same_parent: Result = not is_root and other.parent = parent

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

    	readable: BOOLEAN is True

    	readable_child: BOOLEAN
    			-- Is there a current child to be read?

    	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
    		ensure -- from ANY
    			definition: Result = (conforms_to (other) and other.conforms_to (Current))

    	valid_cursor_index (i: INTEGER_32): BOOLEAN
    			-- Is `i' correctly bounded for cursor movement?
    		ensure
    			valid_cursor_index_definition: Result = (i >= 0) and (i <= child_capacity + 1)

    	writable: BOOLEAN is True
    			-- Is there a current item that may be modified?

    	writable_child: BOOLEAN
    			-- Is there a current child that may be modified?

    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: 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: changeable_comparison_criterion
    		ensure -- from CONTAINER
    			reference_comparison: not object_comparison

    feature -- Cursor movement

    	child_back
    			-- Move cursor to previous child.

    	child_finish
    			-- Move cursor to last child.

    	child_forth
    			-- Move cursor to next child.

    	child_go_i_th (i: INTEGER_32)
    			-- Move cursor to `i'-th child.
    		ensure then
    			position: child_index = i

    	child_go_to (p: CURSOR)
    			-- Move cursor to position `p'.

    	child_start
    			-- Move cursor to first child.

    feature -- Element change

    	child_put (v: like item)
    			-- Put `v' at current child position.
    			-- Was declared in TREE as synonym of child_replace.
    		require
    			child_writable: child_writable
    		ensure
    			item_inserted: child_item = v

    	child_replace (v: like item)
    			-- Put `v' at current child position.
    			-- Was declared in TREE as synonym of child_put.
    		require
    			child_writable: child_writable
    		ensure
    			item_inserted: child_item = v

    	fill (other: TREE [G])
    			-- Fill with as many items of `other' as possible.
    			-- The representations of `other' and current node
    			-- need not be the same.

    	prune (n: like parent)
    			-- Remove `n' from the children.
    		require
    			is_child: n.parent = Current
    		ensure
    			n_is_root: n.is_root

    	put (v: like item)
    			-- Replace element at cursor position by `v'.
    			-- Was declared in TREE as synonym of replace.
    		require
    			is_writable: writable
    		ensure
    			item_inserted: item = v

    	put_child (n: like parent)
    			-- Add `n' to the list of children.
    			-- Do not move child cursor.
    		require
    			non_void_argument: n /= Void

    	replace (v: like item)
    			-- Replace element at cursor position by `v'.
    			-- Was declared in TREE as synonym of put.
    		require
    			is_writable: writable
    		ensure
    			item_inserted: item = v

    	replace_child (n: like parent)
    			-- Put `n' at current child position.
    		require
    			writable_child: writable_child
    		ensure
    			child_replaced: child = n

    	sprout
    			-- Make current node a root.

    feature -- Removal

    	forget_left
    			-- Forget all left siblings.

    	forget_right
    			-- Forget all right siblings.

    	wipe_out
    			-- Remove all children.
    		ensure
    			is_leaf: is_leaf

    feature -- Conversion

    	binary_representation: BINARY_TREE [G]
    			-- Convert to binary tree representation:
    			-- first child becomes left child,
    			-- right sibling becomes right child.
    		ensure
    			result_is_root: Result.is_root
    			result_has_no_right_child: not Result.has_right

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

    feature -- Duplication

    	copy (other: like Current)
    			-- Copy contents from `other'.
    		require -- from ANY
    			other_not_void: other /= Void
    			type_identity: same_type (other)
    		ensure -- from ANY
    			is_equal: is_equal (other)

    	frozen deep_copy (other: like Current)
    			-- Effect equivalent to that of:
    			--		copy (`other' . deep_twin)
    			-- (from ANY)
    		require -- from ANY
    			other_not_void: other /= Void
    		ensure -- from ANY
    			deep_equal: deep_equal (Current, other)

    	frozen deep_twin: like Current
    			-- New object structure recursively duplicated from Current.
    			-- (from ANY)
    		ensure -- from ANY
    			deep_equal: deep_equal (Current, Result)

    	duplicate (n: INTEGER_32): like Current
    			-- Copy of sub-tree beginning at cursor position and
    			-- having min (`n', arity - child_index + 1)
    			-- children.
    		require
    			not_child_off: not child_off
    			valid_sublist: n >= 0

    	frozen standard_copy (other: like Current)
    			-- 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)
    		ensure -- from ANY
    			is_standard_equal: standard_is_equal (other)

    	frozen standard_twin: like Current
    			-- New object field-by-field identical to `other'.
    			-- Always uses default copying semantics.
    			-- (from ANY)
    		ensure -- from ANY
    			standard_twin_not_void: Result /= Void
    			equal: standard_equal (Result, Current)

    	frozen twin: like Current
    			-- New object equal to `Current'
    			-- twin calls copy; to change copying/twining semantics, redefine copy.
    			-- (from ANY)
    		ensure -- from ANY
    			twin_not_void: Result /= Void
    			is_equal: Result.is_equal (Current)

    feature -- Basic operations

    	frozen default: like Current
    			-- Default value of object's type
    			-- (from ANY)

    	frozen default_pointer: POINTER
    			-- Default value of type `POINTER'
    			-- (Avoid the need to write `p'.default for
    			-- some `p' of type `POINTER'.)
    			-- (from ANY)

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

    	frozen do_nothing
    			-- Execute a null action.
    			-- (from ANY)

    feature -- Output

    	io: STD_FILES
    			-- Handle to standard file setup
    			-- (from ANY)

    	out: STRING_8
    			-- New string containing terse printable representation
    			-- of current object
    			-- Was declared in ANY as synonym of tagged_out.
    			-- (from ANY)

    	print (some: ANY)
    			-- Write terse external representation of `some'
    			-- on standard output.
    			-- (from ANY)

    	frozen tagged_out: STRING_8
    			-- New string containing terse printable representation
    			-- of current object
    			-- Was declared in ANY as synonym of out.
    			-- (from ANY)

    feature -- Platform

    	operating_environment: OPERATING_ENVIRONMENT
    			-- Objects available from the operating system
    			-- (from ANY)

    invariant
    	tree_consistency: child_readable implies child.parent = Current
    	leaf_definition: is_leaf = (arity = 0)
    	child_off_definition: child_off = child_before or child_after
    	child_before_definition: child_before = (child_index = 0)
    	child_isfirst_definition: child_isfirst = (not is_leaf and child_index = 1)
    	child_islast_definition: child_islast = (not is_leaf and child_index = child_capacity)
    	child_after_definition: child_after = (child_index >= child_capacity + 1)

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

    indexing
    	library: "EiffelBase: Library of reusable components for Eiffel."
    	copyright: "Copyright (c) 1984-2006, Eiffel Software and others"
    	license: "Eiffel Forum License v2 (see http://www.eiffel.com/licensing/forum.txt)"
    	source: "[
    		Eiffel Software
    		356 Storke Road, 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 TREE