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

class 
	BAG [G -> attached ANY]

create 
	make_empty,
	make_from_array,
	make_from_tuple_array

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 BAG [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
	
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 (other: BAG [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

	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 (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
		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

	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 -- Conversion

	as_array: ARRAY [G]
			-- Return current bag as an array of items.
		local
			i: INTEGER_32
		do
			create Result.make_empty
			across
				imp as map
			loop
				from
					i := 1
				until
					i > map.item.second
				loop
					Result.force (map.item.first, Result.upper + 1)
					i := i + 1
				end
			end
		ensure
			current_bag_unchanged: Current ~ old Current.deep_twin
			same_count: Result.count = # Current
		end

	as_function: FUN [G, INTEGER_32]
			-- Return current bag as a function from items
			-- to number of occurrences.
		local
			pair: PAIR [G, INTEGER_32]
		do
			create Result.make_empty
			across
				imp as cur
			loop
				create pair.make (cur.item.first, cur.item.second)
				Result.extend (pair)
			end
		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
		end

	as_set: SET [G]
			-- Return the domain of curret bag
		do
			create Result.make_empty
			across
				imp as cur
			loop
				Result.extend (cur.item.first)
			end
		ensure
				Result ~ as_function.domain
		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: 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)
		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: BAG [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: BAG [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: 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)
		external
			"built_in"
		ensure -- from ANY
			is_standard_equal: standard_is_equal (other)
		end

	frozen standard_twin: BAG [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: BAG [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 BAG [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 BAG [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 {BAG} -- Implementation

	imp: FUN [G, INTEGER_32]

	set_imp (new_imp: like imp)
		do
			imp := new_imp
		ensure
				imp = new_imp
		end
	
feature -- Commands

	difference (other: like Current)
			-- Subtract 'other' from current bag.
		require
				other |<: Current
		do
			across
				other.imp as cur
			loop
				subtract (cur.item.first, cur.item.second)
			end
		ensure
				Current ~ old Current.deep_twin.differenced (other)
		end

	extend (g: G; i: INTEGER_32)
			-- Add 'g' of quantity 'i' into current bag.
		local
			new_count: INTEGER_32
		do
			if imp.domain.has (g) then
				new_count := imp [g] + i
			else
				new_count := i
			end
			imp.override (create {FUN [G, INTEGER_32]}.make_from_array (<<[g, new_count]>>))
		ensure
				Current ~ old Current.deep_twin.extended (g, i)
		end

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

	override (i: INTEGER_32; g: G)
			-- Change quantity of 'g' to 'i' in current bag
		do
			imp.override (create {FUN [G, INTEGER_32]}.make_from_array (<<[g, i]>>))
		ensure
				Current ~ old Current.deep_twin.overriden (i, g)
		end

	subtract (g: G; i: INTEGER_32)
			-- Subtract 'g' of quantity 'i' from current bag.
		require
				Current [g] >= i
		local
			old_count: INTEGER_32
		do
			old_count := imp [g]
			if old_count = i then
				imp.subtract (create {PAIR [G, INTEGER_32]}.make (g, old_count))
			else
				imp.override (create {FUN [G, INTEGER_32]}.make_from_array (<<[g, old_count - i]>>))
			end
		ensure
				Current ~ old Current.deep_twin.subtracted (g, i)
		end

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

	union (other: like Current)
			-- Add 'other' into current bag.
		do
			across
				other.imp as cur
			loop
				extend (cur.item.first, cur.item.second)
			end
		ensure
				Current ~ old Current.deep_twin.unioned (other)
		end
	
feature -- Constructor

	make_empty
		do
			create imp.make_empty
		end

	make_from_array (a: ARRAY [G])
		do
			make_empty
			across
				a as it
			loop
				extend_by (it.item)
			end
		ensure
				# Current = a.count
		end

	make_from_tuple_array (a: ARRAY [TUPLE [g: G; i: INTEGER_32]])
		require
				across
					a as cur
				all
					cur.item.i > 0
				end
		local
			new_count: INTEGER_32
		do
			make_empty
			across
				a as t
			loop
				new_count := Current [t.item.g] + t.item.i
				imp.override (create {FUN [G, INTEGER_32]}.make_from_array (<<[t.item.g, new_count]>>))
			end
		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
		do
			Result := # Current = # other and then imp ~ other.imp
		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)
		end
	
feature -- Iteration cursor

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

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

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

	print (o: detachable ANY)
			-- Write terse external representation of o
			-- on standard output.
			-- (from ANY)
		do
			if o /= Void then
				Io.put_string (o.out)
			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 -- Quantifiers

	comprehension alias "|" (exp: PREDICATE [PAIR [G, INTEGER_32]]): like Current
			-- Largest subset of the current fun whose elements satisfy exp
		local
			fun: FUN [G, INTEGER_32]
		do
			fun := as_function.comprehension (exp)
			create Result.make_empty
			Result.set_imp (fun)
		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
		end

	hold_count (exp: PREDICATE [PAIR [G, INTEGER_32]]): INTEGER_32
			-- How many items satisfying exp are in Current?
		do
			Result := as_function.hold_count (exp)
		ensure
			current_bag_unchanged: Current ~ old Current.deep_twin
			maximum_result: 0 <= Result and Result <= count
				0 <= Result and Result <= # as_function.domain
		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_8
			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: ")
				create l_exc
				l_msg.append (generating_type.name)
				l_exc.raise_retrieval_exception (l_msg)
			end
		end
	
feature -- Specification Queries

	differenced alias "|\" (other: like Current): like Current
			-- Return a representation of current bag with
			-- 'other' subtracted.
		require
				other |<: Current
		do
			Result := Current.deep_twin
			Result.difference (other)
		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
		end

	extended (g: G; i: INTEGER_32): like Current
			-- Return a representation of current bag with
			-- 'g' of quantity 'i' added.
		do
			Result := Current.deep_twin
			Result.extend (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
		end

	extended_by alias "+" (g: G): like Current
			-- Return a representation of current bag with
			-- 'g' of quantity 1 added.
		do
			Result := Current.deep_twin
			Result.extend_by (g)
		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
		end

	overriden (i: INTEGER_32; g: G): like Current
			-- Return a representation of current bag with
			-- quantity of 'g' to 'i'
		do
			Result := Current.deep_twin
			Result.override (i, g)
		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
		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
		do
			Result := Current.deep_twin
			Result.subtract (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
		end

	subtracted_by alias "-" (g: G): like Current
			-- Return a representation of current bag with
			-- 'g' of quantity 1 subtracted.
		require
				Current [g] >= 1
		do
			Result := Current.deep_twin
			Result.subtract_by (g)
		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
		end

	unioned alias "|\/|" (other: like Current): like Current
			-- Return a representation of current bag with
			-- 'other' added.
		do
			Result := Current.deep_twin
			Result.union (other)
		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
		end
	
feature -- Status queries

	count alias "#": INTEGER_32
		do
			Result := 0
			across
				imp as map
			loop
				Result := Result + map.item.second
			end
		ensure
				Result = as_array.count
		end

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

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

	is_subbag_of alias "|<:" (other: like Current): BOOLEAN
		local
			fun_cur: ITERATION_CURSOR [PAIR [G, INTEGER_32]]
			item: G
			occ: INTEGER_32
		do
			Result := True
			from
				fun_cur := imp.new_cursor
			until
				not Result or else fun_cur.after
			loop
				item := fun_cur.item.first
				occ := fun_cur.item.second
				if other [item] < occ then
					Result := False
				end
				fun_cur.forth
			end
		ensure
				Result = across
					as_function as cur
				all
					cur.item.second <= other [cur.item.first]
				end
		end

	occurrences alias "[]" (g: G): INTEGER_32 assign override
			-- Number of 'g' in current bag.
		do
			if imp.domain.has (g) then
				Result := imp [g]
			else
				Result := 0
			end
		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]
		end
	
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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