indexing
	description: "Terminal constructs with just one specimen, representing a language keyword or special symbol"
	legal: "See notice at end of class."
	status: "See notice at end of class."
	date: "$Date: 2006-01-22 18:25:44 -0800 (Sun, 22 Jan 2006) $"
	revision: "$Revision: 56675 $"

class interface
	KEYWORD

create 
	make (s: STRING_8)
			-- Set up terminal to represent `s'.
		ensure
			construct_name = s
			lex_code = document.keyword_code (s)

feature -- Initialization

	make (s: STRING_8)
			-- Set up terminal to represent `s'.
		ensure
			construct_name = s
			lex_code = document.keyword_code (s)

	construct_make
			-- Set up construct.
			-- (from CONSTRUCT)
	
feature -- Access

	child_cursor: TWO_WAY_TREE_CURSOR [CONSTRUCT]
			-- Current cursor position
			-- (from TWO_WAY_TREE)
		require -- from  CURSOR_STRUCTURE
			True
		require -- from  TREE
			True
		ensure -- from CURSOR_STRUCTURE
			cursor_not_void: Result /= Void

	construct_name: STRING_8
			-- Name of the keyword

	document: INPUT
			-- The document to be parsed
			-- (from CONSTRUCT)

	first: like child_item
			-- Item at first position
			-- (from LINKED_LIST)
		require -- from CHAIN
			not_empty: not is_leaf

	first_child: like parent
			-- Leftmost child
			-- (from TWO_WAY_TREE)

	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)

	i_th alias "[]" (i: INTEGER_32): like child_item assign put_i_th
			-- Item at `i'-th position
			-- Was declared in CHAIN as synonym of infix "@".
			-- (from CHAIN)
		require -- from TABLE
			valid_key: valid_index (i)

	child_index: INTEGER_32
			-- Index of current position
			-- (from LINKED_LIST)
		require -- from  LINEAR
			True
		require -- from  TREE
			True
		ensure -- from TREE
			valid_index: Result >= 0 and Result <= arity + 1

	index_of (v: like child_item; i: INTEGER_32): INTEGER_32
			-- 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: CONSTRUCT
			-- Content of cell.
			-- (from CELL)

	child_item: CONSTRUCT
			-- Current item
			-- (from LINKED_LIST)
		require -- from TRAVERSABLE
			not_off: not child_off
		require -- from ACTIVE
			readable: child_readable
		require -- from TREE
			readable: child_readable

	last: like child_item
			-- Item at last position
			-- (from LINKED_LIST)
		require -- from CHAIN
			not_empty: not is_leaf

	last_child: like parent
			-- (from TWO_WAY_TREE)

	left_sibling: like Current
			-- Left neighbor
			-- (from BI_LINKABLE)

	lex_code: INTEGER_32
			-- Code of keyword in the lexical anayser

	sequential_occurrences (v: like child_item): INTEGER_32
			-- Number of times `v' appears.
			-- (Reference or object equality,
			-- based on object_comparison.)
			-- (from LINEAR)
		require -- from  BAG
			True
		ensure -- from BAG
			non_negative_occurrences: Result >= 0

	right_sibling: like Current
			-- Right neighbor
			-- (from LINKABLE)

	sublist: like Current
			-- Result produced by last split
			-- (from TWO_WAY_LIST)

	token: TOKEN
			-- Token associated with terminal
			-- (from TERMINAL)

	infix "@" (i: INTEGER_32): like child_item assign put_i_th
			-- Item at `i'-th position
			-- Was declared in CHAIN as synonym of i_th.
			-- (from CHAIN)
		require -- from TABLE
			valid_key: valid_index (i)
	
feature -- Measurement

	child_capacity: INTEGER_32
			-- Maximal number of children
			-- (from TREE)

	count: INTEGER_32
			-- Number of items
			-- (from TREE)

	arity: INTEGER_32
			-- Number of items
			-- (from LINKED_LIST)

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

	occurrences (v: like child_item): INTEGER_32
			-- Number of times `v' appears.
			-- (Reference or object equality,
			-- based on object_comparison.)
			-- (from CHAIN)
		require -- from  BAG
			True
		require -- from  LINEAR
			True
		ensure -- from BAG
			non_negative_occurrences: Result >= 0
	
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.)
			-- (from TREE)
		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
		ensure then -- from LIST
			indices_unchanged: child_index = old child_index and other.child_index = old other.child_index
			true_implies_same_size: Result implies arity = other.arity

	node_is_equal (other: like Current): BOOLEAN
			-- Is `other' equal to Current?
			-- (from TREE)
		require -- from TREE
			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

	child_after: BOOLEAN
			-- Is there no valid cursor position to the right of cursor?
			-- (from LINKED_LIST)

	child_before: BOOLEAN
			-- Is there no valid cursor position to the left of cursor?
			-- (from LINKED_LIST)

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

	child_isfirst: BOOLEAN
			-- Is cursor under first child?
			-- (from TREE)
		require -- from  CHAIN
			True
		ensure -- from CHAIN
			valid_position: Result implies not is_leaf
		ensure -- from TREE
			not_is_leaf: Result implies not is_leaf

	child_islast: BOOLEAN
			-- Is cursor under last child?
			-- (from TWO_WAY_TREE)
		require -- from  CHAIN
			True
		require -- from  TREE
			True
		ensure -- from CHAIN
			valid_position: Result implies not is_leaf
		ensure -- from TREE
			not_is_leaf: Result implies not is_leaf

	child_readable: BOOLEAN
			-- Is there a current child_item to be read?
			-- (from TREE)
		require -- from  ACTIVE
			True

	child_writable: BOOLEAN
			-- Is there a current child_item that may be modified?
			-- (from TREE)
		require -- from  ACTIVE
			True

	committed: BOOLEAN
			-- Have enough productions been recognized to interpret
			-- failure of parsing as a syntax error in this construct?
			-- (Otherwise the parsing process will backtrack, trying
			-- other possible interpretations of the part already read.)
			-- (from CONSTRUCT)

	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

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

	child_extendible: BOOLEAN is True
			-- May new items be added? (Answer: yes.)
			-- (from DYNAMIC_CHAIN)

	extendible: BOOLEAN is True
			-- May new items be added?
			-- (from DYNAMIC_TREE)

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

	is_empty: BOOLEAN
			-- Is structure empty of items?
			-- (from TREE)

	is_inserted (v: CONSTRUCT): BOOLEAN
			-- Has `v' been inserted at the end by the most recent put or
			-- extend?
			-- (from LINKED_LIST)

	is_leaf: BOOLEAN
			-- Are there no children?
			-- (from TREE)
		require -- from  CONTAINER
			True

	is_optional: BOOLEAN
			-- Is construct optional? 
			-- (from CONSTRUCT)

	is_root: BOOLEAN
			-- Is there no parent?
			-- (from TREE)

	is_sibling (other: like parent): BOOLEAN
			-- Are current node and `other' siblings?
			-- (from TREE)
		require -- from TREE
			other_exists: other /= Void
		ensure -- from TREE
			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)

	child_off: BOOLEAN
			-- Is there no current item?
			-- (from LINKED_LIST)
		require -- from  TRAVERSABLE
			True
		require -- from  TREE
			True

	parsed: BOOLEAN
			-- Has construct been successfully parsed?
			-- (True for optional components not present)
			-- (from CONSTRUCT)

	print_mode: CELL [BOOLEAN]
			-- Must the left-recursion test also print the production?
			-- (Default: no.)
			-- (from CONSTRUCT)

	prunable: BOOLEAN
			-- May items be removed? (Answer: yes.)
			-- (from DYNAMIC_CHAIN)
		require -- from  COLLECTION
			True

	readable: BOOLEAN is True
			-- (from TREE)

	readable_child: BOOLEAN
			-- Is there a current child to be read?
			-- (from TREE)

	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 (p: CURSOR): BOOLEAN
			-- Can the cursor be moved to position `p'?
			-- (from LINKED_LIST)

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

	valid_index (i: INTEGER_32): BOOLEAN
			-- Is `i' within allowable bounds?
			-- (from CHAIN)
		require -- from  TABLE
			True
		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 <= arity))

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

	writable_child: BOOLEAN
			-- Is there a current child that may be modified?
			-- (from TREE)
	
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

	set_optional
			-- Define this construct as optional.
			-- (from CONSTRUCT)
		ensure -- from CONSTRUCT
			optional_construct: is_optional
	
feature -- Cursor movement

	child_back
			-- Move cursor to previous position, if any.
			-- (from TWO_WAY_LIST)
		require -- from BILINEAR
			not_before: not child_before
		require -- from  TREE
			True

	child_finish
			-- Move cursor to last position.
			-- (Go before if empty)
			-- (from TWO_WAY_LIST)
		require -- from  LINEAR
			True
		require -- from  TREE
			True
		ensure then -- from CHAIN
			at_last: not is_leaf implies child_islast
		ensure then -- from LINKED_LIST
			empty_convention: is_leaf implies child_before
		ensure then -- from TWO_WAY_LIST
			not_after: not child_after

	child_forth
			-- Move cursor to next position, if any.
			-- (from TWO_WAY_LIST)
		require -- from LINEAR
			not_after: not child_after
		require -- from  TREE
			True
		ensure then -- from LIST
			moved_forth: child_index = old child_index + 1

	child_go_i_th (i: INTEGER_32)
			-- Move cursor to `i'-th position.
			-- (from LINKED_LIST)
		require -- from CHAIN
			valid_cursor_index: valid_cursor_index (i)
		require -- from  TREE
			True
		ensure -- from CHAIN
			position_expected: child_index = i
		ensure then -- from TREE
			position: child_index = i

	child_go_to (p: CURSOR)
			-- Move cursor to position `p'.
			-- (from LINKED_LIST)
		require -- from CURSOR_STRUCTURE
			cursor_position_valid: valid_cursor (p)
		require -- from  TREE
			True

	move (i: INTEGER_32)
			-- Move cursor `i' positions. The cursor
			-- may end up `off' if the offset is to big.
			-- (from TWO_WAY_LIST)
		require -- from  CHAIN
			True
		ensure -- from CHAIN
			too_far_right: (old child_index + i > arity) implies exhausted
			too_far_left: (old child_index + i < 1) implies exhausted
			expected_index: (not exhausted) implies (child_index = old child_index + i)
		ensure then -- from LINKED_LIST
			moved_if_inbounds: ((old child_index + i) >= 0 and (old child_index + i) <= (arity + 1)) implies child_index = (old child_index + i)
			before_set: (old child_index + i) <= 0 implies child_before
			after_set: (old child_index + i) >= (arity + 1) implies child_after

	search_child (v: like child_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, child_item)
			item_found: (not exhausted and not object_comparison) implies v = child_item

	child_start
			-- Move cursor to first position.
			-- (from LINKED_LIST)
		require -- from  TRAVERSABLE
			True
		require -- from  TREE
			True
		ensure then -- from CHAIN
			at_first: not is_leaf implies child_isfirst
		ensure then -- from LINKED_LIST
			empty_convention: is_leaf implies child_after
	
feature -- Element change

	append (s: SEQUENCE [CONSTRUCT])
			-- Append a copy of `s'.
			-- (from CHAIN)
		require -- from SEQUENCE
			argument_not_void: s /= Void
		ensure -- from SEQUENCE
			new_count: arity >= old arity

	extend (v: like item)
			-- Add `v' as new child.
			-- (from DYNAMIC_TREE)

	child_extend (v: like child_item)
			-- Add `v' to end.
			-- Do not move cursor.
			-- (from TWO_WAY_LIST)
		require -- from COLLECTION
			extendible: child_extendible
		require -- from  DYNAMIC_TREE
			True
		ensure -- from COLLECTION
			item_inserted: is_inserted (v)
		ensure then -- from BAG
			one_more_occurrence: occurrences (v) = old (occurrences (v)) + 1

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

	force (v: like child_item)
			-- Add `v' to end.
			-- (from SEQUENCE)
		require -- from SEQUENCE
			extendible: child_extendible
		ensure then -- from SEQUENCE
			new_count: arity = old arity + 1
			item_inserted: has (v)

	twl_merge_left (other: like Current)
			-- Merge `other' into current structure before cursor
			-- position. Do not move cursor. Empty `other'.
			-- (from TWO_WAY_LIST)
		require -- from DYNAMIC_CHAIN
			extendible: child_extendible
			not_before: not child_before
			other_exists: other /= Void
			not_current: other /= Current
		ensure -- from DYNAMIC_CHAIN
			new_count: arity = old arity + old other.arity
			new_index: child_index = old child_index + old other.arity
			other_is_empty: other.is_leaf

	twl_merge_right (other: like Current)
			-- Merge `other' into current structure after cursor
			-- position. Do not move cursor. Empty `other'.
			-- (from TWO_WAY_LIST)
		require -- from DYNAMIC_CHAIN
			extendible: child_extendible
			not_after: not child_after
			other_exists: other /= Void
			not_current: other /= Current
		ensure -- from DYNAMIC_CHAIN
			new_count: arity = old arity + old other.arity
			same_index: child_index = old child_index
			other_is_empty: other.is_leaf

	merge_tree_after (other: like first_child)
			-- Merge children of `other' into current structure
			-- after cursor position. Do not move cursor.
			-- Make `other' a leaf.
			-- (from TWO_WAY_TREE)
		require -- from DYNAMIC_TREE
			not_child_off: not child_off
			other_exists: (other /= Void)
		ensure -- from DYNAMIC_TREE
			other_is_leaf: other.is_leaf

	merge_tree_before (other: like first_child)
			-- Merge children of `other' into current structure
			-- before cursor position. Do not move cursor.
			-- Make `other' a leaf.
			-- (from TWO_WAY_TREE)
		require -- from DYNAMIC_TREE
			not_child_off: not child_off
			other_exists: (other /= Void)
		ensure -- from DYNAMIC_TREE
			other_is_leaf: other.is_leaf

	prune (n: like first_child)
			-- Prune `n' from children.
			-- (from TWO_WAY_TREE)
		require -- from TREE
			is_child: n.parent = Current
		ensure -- from TREE
			n_is_root: n.is_root

	child_put (v: like child_item)
			-- Replace current item by `v'.
			-- (Synonym for replace)
			-- (from CHAIN)
		require -- from COLLECTION
			extendible: child_extendible
		require -- from TREE
			child_writable: child_writable
		ensure -- from COLLECTION
			item_inserted: is_inserted (v)
		ensure -- from TREE
			item_inserted: child_item = v
		ensure then -- from CHAIN
			same_count: arity = old arity

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

	put_child_left (n: like parent)
			-- Add `n' to the left of cursor position.
			-- Do not move cursor.
			-- (from TWO_WAY_TREE)
		require -- from DYNAMIC_TREE
			not_child_before: not child_before
			non_void_argument: n /= Void

	put_child_right (n: like parent)
			-- Add `n' to the right of cursor position.
			-- Do not move cursor.
			-- (from TWO_WAY_TREE)
		require -- from DYNAMIC_TREE
			not_child_after: not child_after
			non_void_argument: n /= Void

	put_front (v: like child_item)
			-- Add `v' to beginning.
			-- Do not move cursor.
			-- (from TWO_WAY_LIST)
		require -- from  DYNAMIC_CHAIN
			True
		ensure -- from DYNAMIC_CHAIN
			new_count: arity = old arity + 1
			item_inserted: first = v

	put_i_th (v: like child_item; i: INTEGER_32)
			-- Put `v' at `i'-th position.
			-- (from CHAIN)
		require -- from TABLE
			valid_key: valid_index (i)
		ensure then -- from INDEXABLE
			insertion_done: i_th (i) = v

	child_put_left (v: like child_item)
			-- Add `v' to the left of cursor position.
			-- Do not move cursor.
			-- (from TWO_WAY_LIST)
		require -- from DYNAMIC_CHAIN
			extendible: child_extendible
			not_before: not child_before
		require -- from DYNAMIC_TREE
			not_child_before: not child_before
		ensure -- from DYNAMIC_CHAIN
			new_count: arity = old arity + 1
			new_index: child_index = old child_index + 1
		ensure then -- from LINKED_LIST
			previous_exists: previous /= Void
			item_inserted: previous.item = v

	child_put_right (v: like child_item)
			-- Add `v' to the right of cursor position.
			-- Do not move cursor.
			-- (from TWO_WAY_LIST)
		require -- from DYNAMIC_CHAIN
			extendible: child_extendible
			not_after: not child_after
		require -- from DYNAMIC_TREE
			not_child_after: not child_after
		ensure -- from DYNAMIC_CHAIN
			new_count: arity = old arity + 1
			same_index: child_index = old child_index
		ensure then -- from LINKED_LIST
			next_exists: next /= Void
			item_inserted: not old child_before implies next.item = v
			item_inserted_before: old child_before implies child.item = v

	replace (v: like item)
			-- Make `v' the cell's item.
			-- Was declared in CELL as synonym of put.
			-- (from CELL)
		require -- from TREE
			is_writable: writable
		ensure -- from TREE
			item_inserted: item = v
		ensure -- from CELL
			item_inserted: item = v

	child_replace (v: like child_item)
			-- Replace current item by `v'.
			-- (from LINKED_LIST)
		require -- from ACTIVE
			writable: child_writable
		require -- from TREE
			child_writable: child_writable
		ensure -- from ACTIVE
			item_replaced: child_item = v
		ensure -- from TREE
			item_inserted: child_item = v

	replace_child (n: like parent)
			-- Replace current child by `n'.
			-- (from TWO_WAY_TREE)
		require -- from TREE
			writable_child: writable_child
		ensure -- from TREE
			child_replaced: child = n

	sprout
			-- Make current node a root.
			-- (from TREE)
	
feature -- Removal

	twl_prune (v: like child_item)
			-- Remove first occurrence of `v', if any,
			-- after cursor position.
			-- If found, move cursor to right neighbor;
			-- if not, make structure exhausted.
			-- (from DYNAMIC_CHAIN)
		require -- from COLLECTION
			prunable: prunable

	prune_all (v: like child_item)
			-- Remove all occurrences of `v'.
			-- (Reference or object equality,
			-- based on object_comparison.)
			-- Leave structure exhausted.
			-- (from DYNAMIC_CHAIN)
		require -- from COLLECTION
			prunable: prunable
		ensure -- from COLLECTION
			no_more_occurrences: not has (v)
		ensure then -- from DYNAMIC_CHAIN
			is_exhausted: exhausted

	remove_child
			-- Remove current item.
			-- Move cursor to right neighbor
			-- (or `after' if no right neighbor).
			-- (from TWO_WAY_LIST)
		require -- from ACTIVE
			prunable: prunable
			writable: child_writable
		require -- from DYNAMIC_TREE
			child_not_off: not child_off
		ensure then -- from DYNAMIC_LIST
			after_when_empty: is_leaf implies child_after
		ensure -- from DYNAMIC_TREE
			new_arity: arity = old arity - 1
			new_child_index: child_index = old child_index

	remove_left_child
			-- Remove item to the left of cursor position.
			-- Do not move cursor.
			-- (from TWO_WAY_LIST)
		require -- from DYNAMIC_CHAIN
			left_exists: child_index > 1
		require -- from DYNAMIC_TREE
			is_not_first: not child_isfirst
		ensure -- from DYNAMIC_CHAIN
			new_count: arity = old arity - 1
			new_index: child_index = old child_index - 1
		ensure -- from DYNAMIC_TREE
			new_arity: arity = old arity - 1
			new_child_index: child_index = old child_index - 1

	remove_right_child
			-- Remove item to the right of cursor position.
			-- Do not move cursor.
			-- (from TWO_WAY_LIST)
		require -- from DYNAMIC_CHAIN
			right_exists: child_index < arity
		require -- from DYNAMIC_TREE
			is_not_last: not child_islast
		ensure -- from DYNAMIC_CHAIN
			new_count: arity = old arity - 1
			same_index: child_index = old child_index
		ensure -- from DYNAMIC_TREE
			new_arity: arity = old arity - 1
			new_child_index: child_index = old child_index

	remove_sublist
			-- (from TWO_WAY_LIST)

	split (n: INTEGER_32)
			-- Remove from current list
			-- min (`n', count - `index' - 1) items
			-- starting at cursor position.
			-- Move cursor right one position.
			-- Make extracted sublist accessible
			-- through attribute sublist.
			-- (from TWO_WAY_LIST)
		require -- from TWO_WAY_LIST
			not_off: not child_off
			valid_sublist: n >= 0

	wipe_out
			-- Remove all items.
			-- (from TWO_WAY_LIST)
		require -- from COLLECTION
			prunable: prunable
		require -- from  TREE
			True
		ensure -- from COLLECTION
			wiped_out: is_leaf
		ensure then -- from DYNAMIC_LIST
			is_before: child_before
		ensure -- from TREE
			is_leaf: is_leaf
	
feature -- Transformation

	commit
			-- If this construct is one among several possible ones,
			-- discard the others.
			-- By default this does nothing.
			-- (from CONSTRUCT)

	parse
			-- Attempt to analyze incoming lexical
			-- tokens according to current construct. 
			-- Set parsed to true if successful; 
			-- return to original position in input otherwise.
			-- (from CONSTRUCT)

	unused_pre_action
			-- Semantic action executed before construct is parsed
			-- (nothing by default; may be redefined in descendants).
			-- (from CONSTRUCT)

	process
			-- Parse a specimen of the construct, then apply
			-- semantic actions if parsing successful.
			-- (from CONSTRUCT)

	semantics
			-- Apply semantic actions in order:
			-- `pre_action', in_action, `post_action'.
			-- (from CONSTRUCT)

	swap (i: INTEGER_32)
			-- Exchange item at `i'-th position with item
			-- at cursor position.
			-- (from CHAIN)
		require -- from CHAIN
			not_off: not child_off
			valid_index: valid_index (i)
		ensure -- from CHAIN
			swapped_to_item: child_item = old i_th (i)
			swapped_from_item: i_th (i) = old child_item
	
feature -- Conversion

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

	fill_from_binary (b: BINARY_TREE [CONSTRUCT])
			-- Fill from a binary tree representation.
			-- Left child becomes first child.
			-- Right child becomes right sibling.
			-- Any right child of `b' is ignored.
			-- (from DYNAMIC_TREE)

	linear_representation: LINEAR [CONSTRUCT]
			-- Representation as a linear structure
			-- (from TREE)
		require -- from  CONTAINER
			True
	
feature -- Duplication

	copy (other: like Current)
			-- Copy contents from `other'.
			-- (from TREE)
		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
			-- (from DYNAMIC_TREE)
		require -- from TREE
			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 -- Implementation

	child: like first_child
			-- Element at cursor position
			-- (from LINKED_LIST)

	forget_left
			-- Remove links with left neighbor.
			-- (from BI_LINKABLE)
		require -- from  TREE
			True
		ensure -- from BI_LINKABLE
			left_not_chained: left_sibling = Void or else (old left_sibling /= Void) implies ((old left_sibling).right_sibling = Void)

	forget_right
			-- Remove links with right neighbor.
			-- (from BI_LINKABLE)
		require -- from  LINKABLE
			True
		require -- from  TREE
			True
		ensure -- from LINKABLE
			not_chained: right_sibling = Void
		ensure then -- from BI_LINKABLE
			right_not_chained: (old right_sibling /= Void) implies ((old right_sibling).left_sibling = Void)
	
feature -- Iteration

	do_all (action: PROCEDURE [ANY, TUPLE [CONSTRUCT]])
			-- 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 [CONSTRUCT]]; test: FUNCTION [ANY, TUPLE [CONSTRUCT], 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 [CONSTRUCT], BOOLEAN]): BOOLEAN
			-- Is `test' true for all items?
			-- Semantics not guaranteed if `test' changes the structure;
			-- in such a case, apply iterator to clone of structure instead.
			-- (from LINEAR)
		require -- from TRAVERSABLE
			test_exits: test /= Void
		ensure then -- from LINEAR
			empty: is_leaf implies Result

	there_exists (test: FUNCTION [ANY, TUPLE [CONSTRUCT], BOOLEAN]): BOOLEAN
			-- Is `test' true for at least one item?
			-- Semantics not guaranteed if `test' changes the structure;
			-- in such a case, apply iterator to clone of structure instead.
			-- (from LINEAR)
		require -- from TRAVERSABLE
			test_exits: test /= Void
	
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 -- Output 

	print_name
			-- Print the construct name on standard output.
			-- (from CONSTRUCT)
	
feature -- Platform

	operating_environment: OPERATING_ENVIRONMENT
			-- Objects available from the operating system
			-- (from ANY)
	
invariant
		-- from TWO_WAY_TREE
	off_constraint: (child = Void) implies child_off

		-- from DYNAMIC_TREE
	extendible_definition: extendible
	child_after_definition: child_after = (child_index = arity + 1)

		-- from TREE
	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)

		-- from BI_LINKABLE
	right_symmetry: (right_sibling /= Void) implies (right_sibling.left_sibling = Current)
	left_symmetry: (left_sibling /= Void) implies (left_sibling.right_sibling = Current)

		-- from TWO_WAY_LIST
	non_empty_list_has_two_endpoints: not is_leaf implies (first_child /= Void and last_child /= Void)
	first_element_constraint: first_child /= Void implies first_child.left_sibling = Void
	last_element_constraint: last_child /= Void implies last_child.right_sibling = Void

		-- from LINKED_LIST
	prunable: prunable
	empty_constraint: is_leaf implies ((first_child = Void) and (child = Void))
	not_void_unless_empty: (child = Void) implies is_leaf
	before_constraint: child_before implies (child = first_child)
	after_constraint: child_after implies (child = last_child)

		-- from LIST
	before_definition: child_before = (child_index = 0)
	after_definition: child_after = (child_index = arity + 1)

		-- from CHAIN
	non_negative_index: child_index >= 0
	index_small_enough: child_index <= arity + 1
	off_definition: child_off = ((child_index = 0) or (child_index = arity + 1))
	isfirst_definition: child_isfirst = ((not is_leaf) and (child_index = 1))
	islast_definition: child_islast = ((not is_leaf) and (child_index = arity))
	item_corresponds_to_index: (not child_off) implies (child_item = i_th (child_index))
	index_set_has_same_count: index_set.count = arity

		-- from ACTIVE
	writable_constraint: child_writable implies child_readable
	empty_constraint: is_leaf implies (not child_readable) and (not child_writable)

		-- from INDEXABLE
	index_set_not_void: index_set /= Void

		-- from BILINEAR
	not_both: not (child_after and child_before)
	before_constraint: child_before implies child_off

		-- from LINEAR
	after_constraint: child_after implies child_off

		-- from TRAVERSABLE
	empty_constraint: is_leaf implies child_off

		-- from FINITE
	empty_definition: is_leaf = (arity = 0)
	non_negative_count: arity >= 0

		-- from DYNAMIC_CHAIN
	extendible: child_extendible

indexing
	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 KEYWORD