note
	description: "Collections with membership multilicity"
	author: "JSO, Jackie Wang"
	date: "$Date$"
	revision: "$Revision$"

class interface
	BAG [G -> attached ANY]

create 
	make_empty

	make_from_array (a: ARRAY [G])
		ensure
				# Current = a.count

	make_from_tuple_array (a: ARRAY [TUPLE [g: G; i: INTEGER_32]])
		require
				across
					a as cur
				all
					cur.item.i > 0
				end

feature -- Access

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

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

	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)
		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))

	frozen is_deep_equal (other: BAG [G]): BOOLEAN
			-- Are Current and other attached to isomorphic object structures?
			-- (from ANY)
		require -- from ANY
			other_not_void: other /= Void
		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)

	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)
		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))

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

	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))
	
feature -- Conversion

	as_array: ARRAY [G]
			-- Return current bag as an array of items.
		ensure
			current_bag_unchanged: Current ~ old Current.deep_twin
			same_count: Result.count = # Current

	as_function: FUN [G, INTEGER_32]
			-- Return current bag as a function from items
			-- to number of occurrences.
		ensure
			all_bag_items_covered: across
					Current as cur
				all
					Current [cur.item.first] = Result [cur.item.first]
				end
			only_bag_items_covered: across
					Result as cur
				all
					Current [cur.item.first] = Result [cur.item.first]
				end

	as_set: SET [G]
			-- Return the domain of curret bag
		ensure
				Result ~ as_function.domain
	
feature -- Duplication

	copy (other: BAG [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)
		ensure -- from ANY
			is_equal: Current ~ other

	frozen deep_copy (other: BAG [G])
			-- 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: BAG [G]
			-- New object structure recursively duplicated from Current.
			-- (from ANY)
		ensure -- from ANY
			deep_twin_not_void: Result /= Void
			deep_equal: deep_equal (Current, Result)

	frozen standard_copy (other: BAG [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)
		ensure -- from ANY
			is_standard_equal: standard_is_equal (other)

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

	frozen default: detachable BAG [G]
			-- 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)
		ensure -- from ANY
			instance_free: class

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

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

	difference (other: like Current)
			-- Subtract 'other' from current bag.
		require
				other |<: Current
		ensure
				Current ~ old Current.deep_twin.differenced (other)

	extend (g: G; i: INTEGER_32)
			-- Add 'g' of quantity 'i' into current bag.
		ensure
				Current ~ old Current.deep_twin.extended (g, i)

	extend_by (g: G)
			-- Add 'g' of quantity 1 into current bag.
		ensure
				Current ~ old Current.deep_twin.extended_by (g)

	override (i: INTEGER_32; g: G)
			-- Change quantity of 'g' to 'i' in current bag
		ensure
				Current ~ old Current.deep_twin.overriden (i, g)

	subtract (g: G; i: INTEGER_32)
			-- Subtract 'g' of quantity 'i' from current bag.
		require
				Current [g] >= i
		ensure
				Current ~ old Current.deep_twin.subtracted (g, i)

	subtract_by (g: G)
			-- Subtract 'g' of quantity 1 from current bag.
		require
				Current [g] >= 1
		ensure
				Current ~ old Current.deep_twin.subtracted_by (g)

	union (other: like Current)
			-- Add 'other' into current bag.
		ensure
				Current ~ old Current.deep_twin.unioned (other)
	
feature -- Constructor

	make_empty

	make_from_array (a: ARRAY [G])
		ensure
				# Current = a.count

	make_from_tuple_array (a: ARRAY [TUPLE [g: G; i: INTEGER_32]])
		require
				across
					a as cur
				all
					cur.item.i > 0
				end
	
feature -- Equality

	is_equal (other: like Current): BOOLEAN
			-- Is other attached to an object considered
			-- equal to current object?
		require -- from ANY
			other_not_void: other /= Void
		ensure -- from ANY
			symmetric: Result implies other ~ Current
			consistent: standard_is_equal (other) implies Result
		ensure then
				Result = (Current |<: other and other |<: Current)
				Result = (as_function ~ other.as_function)
	
feature -- Iteration cursor

	new_cursor: ITERATION_CURSOR [PAIR [G, INTEGER_32]]
			-- Fresh cursor associated with current structure
		ensure -- from ITERABLE
			result_attached: Result /= Void
	
feature -- Output

	debug_output: STRING_8
			-- Return a string representation of current bag
			-- for debugging
		require -- from  DEBUG_OUTPUT
			True
		ensure -- from DEBUG_OUTPUT
			result_not_void: Result /= Void
		ensure then
				Result ~ out

	Io: STD_FILES
			-- Handle to standard file setup
			-- (from ANY)
		ensure -- from ANY
			instance_free: class
			io_not_void: Result /= Void

	out: STRING_8
			-- Return a string representation of current bag
		require -- from  ANY
			True
		ensure -- from ANY
			out_not_void: Result /= Void
		ensure then
				Result ~ as_function.out

	print (o: detachable ANY)
			-- Write terse external representation of o
			-- on standard output.
			-- (from ANY)
		ensure -- from ANY
			instance_free: class

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

	Operating_environment: OPERATING_ENVIRONMENT
			-- Objects available from the operating system
			-- (from ANY)
		ensure -- from ANY
			instance_free: class
			operating_environment_not_void: Result /= Void
	
feature -- Quantifiers

	comprehension alias "|" (exp: PREDICATE [PAIR [G, INTEGER_32]]): like Current
			-- Largest subset of the current fun whose elements satisfy exp
		ensure
			current_bag_unchanged: Current ~ old Current.deep_twin
			is_subset: Result |<: Current
			all_satisfying_exp: Result.hold_count (exp) = # Result.as_set
			consistent_satisfying_items: Current.hold_count (exp) = # Result.as_set

	hold_count (exp: PREDICATE [PAIR [G, INTEGER_32]]): INTEGER_32
			-- How many items satisfying exp are in Current?
		ensure
			current_bag_unchanged: Current ~ old Current.deep_twin
			maximum_result: 0 <= Result and Result <= count
				0 <= Result and Result <= # as_function.domain
	
feature -- Specification Queries

	differenced alias "|\" (other: like Current): like Current
			-- Return a representation of current bag with
			-- 'other' subtracted.
		require
				other |<: Current
		ensure
			current_bag_unchanged: Current ~ old Current.deep_twin
				across
					Result as cur
				all
					(other.has (cur.item.first) implies Result [cur.item.first] = Current [cur.item.first] - other [cur.item.first]) and (not other.has (cur.item.first) implies Result [cur.item.first] = Current [cur.item.first])
				end

	extended (g: G; i: INTEGER_32): like Current
			-- Return a representation of current bag with
			-- 'g' of quantity 'i' added.
		ensure
			current_bag_unchanged: Current ~ old Current.deep_twin
				across
					Result as cur
				all
					(cur.item.first ~ g implies Result [cur.item.first] = Current [cur.item.first] + i) and (cur.item.first /~ g implies Result [cur.item.first] = Current [cur.item.first])
				end

	extended_by alias "+" (g: G): like Current
			-- Return a representation of current bag with
			-- 'g' of quantity 1 added.
		ensure
			current_bag_unchanged: Current ~ old Current.deep_twin
				across
					Result as cur
				all
					(cur.item.first ~ g implies Result [cur.item.first] = Current [cur.item.first] + 1) and (cur.item.first /~ g implies Result [cur.item.first] = Current [cur.item.first])
				end

	overriden (i: INTEGER_32; g: G): like Current
			-- Return a representation of current bag with
			-- quantity of 'g' to 'i'
		ensure
			current_bag_unchanged: Current ~ old Current.deep_twin
				across
					Result as cur
				all
					(cur.item.first ~ g implies Result [cur.item.first] = i) and (cur.item.first /~ g implies Result [cur.item.first] = Current [cur.item.first])
				end

	subtracted (g: G; i: INTEGER_32): like Current
			-- Return a representation of current bag with
			-- 'g' of quantity 'i' subtracted.
		require
				Current [g] >= i
		ensure
			current_bag_unchanged: Current ~ old Current.deep_twin
				across
					Result as cur
				all
					(cur.item.first ~ g implies Result [cur.item.first] = Current [cur.item.first] - i) and (cur.item.first /~ g implies Result [cur.item.first] = Current [cur.item.first])
				end

	subtracted_by alias "-" (g: G): like Current
			-- Return a representation of current bag with
			-- 'g' of quantity 1 subtracted.
		require
				Current [g] >= 1
		ensure
			current_bag_unchanged: Current ~ old Current.deep_twin
				across
					Result as cur
				all
					(cur.item.first ~ g implies Result [cur.item.first] = Current [cur.item.first] - 1) and (cur.item.first /~ g implies Result [cur.item.first] = Current [cur.item.first])
				end

	unioned alias "|\/|" (other: like Current): like Current
			-- Return a representation of current bag with
			-- 'other' added.
		ensure
			current_bag_unchanged: Current ~ old Current.deep_twin
				across
					Result as cur
				all
					(other.has (cur.item.first) implies Result [cur.item.first] = Current [cur.item.first] + other [cur.item.first]) and (not other.has (cur.item.first) implies Result [cur.item.first] = Current [cur.item.first])
				end
	
feature -- Status queries

	count alias "#": INTEGER_32
		ensure
				Result = as_array.count

	has (g: G): BOOLEAN
		ensure
				Result = as_array.has (g)
				Result = as_function.domain.has (g)
				Result = (Current [g] > 0)

	is_empty: BOOLEAN
		ensure
				Result = (# Current = 0)

	is_subbag_of alias "|<:" (other: like Current): BOOLEAN
		ensure
				Result = across
					as_function as cur
				all
					cur.item.second <= other [cur.item.first]
				end

	occurrences alias "[]" (g: G): INTEGER_32 assign override
			-- Number of 'g' in current bag.
		ensure
			non_negative_occurrences: Result >= 0
			case_of_nonmember: not has (g) implies Result = 0
			case_of_member: has (g) implies Result > 0 and Result = as_function [g]
	
invariant
	bag_not_containing_zero_occurrence_item: across
			Current as pair
		all
			pair.item.second > 0
		end

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

end -- class BAG

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