/* Part of SWI-Prolog Author: Jan Wielemaker and Jon Jagger E-mail: J.Wielemaker@vu.nl WWW: http://www.swi-prolog.org Copyright (c) 2001-2021, University of Amsterdam VU University Amsterdam SWI-Prolog Solutions b.v. All rights reserved. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: 1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. 2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution. THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. */ :- module(ordsets, [ is_ordset/1, % @Term list_to_ord_set/2, % +List, -OrdSet ord_add_element/3, % +Set, +Element, -NewSet ord_del_element/3, % +Set, +Element, -NewSet ord_selectchk/3, % +Item, ?Set1, ?Set2 ord_intersect/2, % +Set1, +Set2 (test non-empty) ord_intersect/3, % +Set1, +Set2, -Intersection ord_intersection/3, % +Set1, +Set2, -Intersection ord_intersection/4, % +Set1, +Set2, -Intersection, -Diff ord_disjoint/2, % +Set1, +Set2 ord_subtract/3, % +Set, +Delete, -Remaining ord_union/2, % +SetOfOrdSets, -Set ord_union/3, % +Set1, +Set2, -Union ord_union/4, % +Set1, +Set2, -Union, -New ord_subset/2, % +Sub, +Super (test Sub is in Super) % Non-Quintus extensions ord_empty/1, % ?Set ord_memberchk/2, % +Element, +Set, ord_symdiff/3, % +Set1, +Set2, ?Diff % SICSTus extensions ord_seteq/2, % +Set1, +Set2 ord_intersection/2 % +PowerSet, -Intersection ]). :- use_module(library(error)). :- set_prolog_flag(generate_debug_info, false). /** Ordered set manipulation Ordered sets are lists with unique elements sorted to the standard order of terms (see sort/2). Exploiting ordering, many of the set operations can be expressed in order N rather than N^2 when dealing with unordered sets that may contain duplicates. The library(ordsets) is available in a number of Prolog implementations. Our predicates are designed to be compatible with common practice in the Prolog community. The implementation is incomplete and relies partly on library(oset), an older ordered set library distributed with SWI-Prolog. New applications are advised to use library(ordsets). Some of these predicates match directly to corresponding list operations. It is advised to use the versions from this library to make clear you are operating on ordered sets. An exception is member/2. See ord_memberchk/2. The ordsets library is based on the standard order of terms. This implies it can handle all Prolog terms, including variables. Note however, that the ordering is not stable if a term inside the set is further instantiated. Also note that variable ordering changes if variables in the set are unified with each other or a variable in the set is unified with a variable that is `older' than the newest variable in the set. In practice, this implies that it is allowed to use member(X, OrdSet) on an ordered set that holds variables only if X is a fresh variable. In other cases one should cease using it as an ordset because the order it relies on may have been changed. */ %! is_ordset(@Term) is semidet. % % True if Term is an ordered set. All predicates in this library % expect ordered sets as input arguments. Failing to fullfil this % assumption results in undefined behaviour. Typically, ordered % sets are created by predicates from this library, sort/2 or % setof/3. is_ordset(Term) :- is_list(Term), is_ordset2(Term). is_ordset2([]). is_ordset2([H|T]) :- is_ordset3(T, H). is_ordset3([], _). is_ordset3([H2|T], H) :- H2 @> H, is_ordset3(T, H2). %! ord_empty(?List) is semidet. % % True when List is the empty ordered set. Simply unifies list % with the empty list. Not part of Quintus. ord_empty([]). %! ord_seteq(+Set1, +Set2) is semidet. % % True if Set1 and Set2 have the same elements. As both are % canonical sorted lists, this is the same as ==/2. % % @compat sicstus ord_seteq(Set1, Set2) :- Set1 == Set2. %! list_to_ord_set(+List, -OrdSet) is det. % % Transform a list into an ordered set. This is the same as % sorting the list. list_to_ord_set(List, Set) :- sort(List, Set). %! ord_intersect(+Set1, +Set2) is semidet. % % True if both ordered sets have a non-empty intersection. ord_intersect([H1|T1], L2) :- ord_intersect_(L2, H1, T1). ord_intersect_([H2|T2], H1, T1) :- compare(Order, H1, H2), ord_intersect__(Order, H1, T1, H2, T2). ord_intersect__(<, _H1, T1, H2, T2) :- ord_intersect_(T1, H2, T2). ord_intersect__(=, _H1, _T1, _H2, _T2). ord_intersect__(>, H1, T1, _H2, T2) :- ord_intersect_(T2, H1, T1). %! ord_disjoint(+Set1, +Set2) is semidet. % % True if Set1 and Set2 have no common elements. This is the % negation of ord_intersect/2. ord_disjoint(Set1, Set2) :- \+ ord_intersect(Set1, Set2). %! ord_intersect(+Set1, +Set2, -Intersection) % % Intersection holds the common elements of Set1 and Set2. % % @deprecated Use ord_intersection/3 ord_intersect(Set1, Set2, Intersection) :- ord_intersection(Set1, Set2, Intersection). %! ord_intersection(+PowerSet, -Intersection) is semidet. % % Intersection of a powerset. True when Intersection is an ordered set % holding all elements common to all sets in PowerSet. Fails if % PowerSet is an empty list. % % @compat sicstus ord_intersection(PowerSet, Intersection) :- must_be(list, PowerSet), key_by_length(PowerSet, Pairs), keysort(Pairs, [_-S|Sorted]), l_int(Sorted, S, Intersection). key_by_length([], []). key_by_length([H|T0], [L-H|T]) :- '$skip_list'(L, H, Tail), ( Tail == [] -> key_by_length(T0, T) ; type_error(list, H) ). l_int(_, [], I) => I = []. l_int([], S, I) => I = S. l_int([_-H|T], S0, S) => ord_intersection(S0, H, S1), l_int(T, S1, S). %! ord_intersection(+Set1, +Set2, -Intersection) is det. % % Intersection holds the common elements of Set1 and Set2. Uses % ord_disjoint/2 if Intersection is bound to `[]` on entry. ord_intersection(Set1, Set2, Intersection) :- ( Intersection == [] -> ord_disjoint(Set1, Set2) ; ord_intersection_(Set1, Set2, Intersection) ). ord_intersection_([], _Int, []). ord_intersection_([H1|T1], L2, Int) :- isect2(L2, H1, T1, Int). isect2([], _H1, _T1, []). isect2([H2|T2], H1, T1, Int) :- compare(Order, H1, H2), isect3(Order, H1, T1, H2, T2, Int). isect3(<, _H1, T1, H2, T2, Int) :- isect2(T1, H2, T2, Int). isect3(=, H1, T1, _H2, T2, [H1|Int]) :- ord_intersection_(T1, T2, Int). isect3(>, H1, T1, _H2, T2, Int) :- isect2(T2, H1, T1, Int). %! ord_intersection(+Set1, +Set2, ?Intersection, ?Difference) is det. % % Intersection and difference between two ordered sets. % Intersection is the intersection between Set1 and Set2, while % Difference is defined by ord_subtract(Set2, Set1, Difference). % % @see ord_intersection/3 and ord_subtract/3. ord_intersection([], L, [], L) :- !. ord_intersection([_|_], [], [], []) :- !. ord_intersection([H1|T1], [H2|T2], Intersection, Difference) :- compare(Diff, H1, H2), ord_intersection2(Diff, H1, T1, H2, T2, Intersection, Difference). ord_intersection2(=, H1, T1, _H2, T2, [H1|T], Difference) :- ord_intersection(T1, T2, T, Difference). ord_intersection2(<, _, T1, H2, T2, Intersection, Difference) :- ord_intersection(T1, [H2|T2], Intersection, Difference). ord_intersection2(>, H1, T1, H2, T2, Intersection, [H2|HDiff]) :- ord_intersection([H1|T1], T2, Intersection, HDiff). %! ord_add_element(+Set1, +Element, ?Set2) is det. % % Insert an element into the set. This is the same as % ord_union(Set1, [Element], Set2). ord_add_element([], El, [El]). ord_add_element([H|T], El, Add) :- compare(Order, H, El), addel(Order, H, T, El, Add). addel(<, H, T, El, [H|Add]) :- ord_add_element(T, El, Add). addel(=, H, T, _El, [H|T]). addel(>, H, T, El, [El,H|T]). %! ord_del_element(+Set, +Element, -NewSet) is det. % % Delete an element from an ordered set. This is the same as % ord_subtract(Set, [Element], NewSet). ord_del_element([], _El, []). ord_del_element([H|T], El, Del) :- compare(Order, H, El), delel(Order, H, T, El, Del). delel(<, H, T, El, [H|Del]) :- ord_del_element(T, El, Del). delel(=, _H, T, _El, T). delel(>, H, T, _El, [H|T]). %! ord_selectchk(+Item, ?Set1, ?Set2) is semidet. % % Selectchk/3, specialised for ordered sets. Is true when % select(Item, Set1, Set2) and Set1, Set2 are both sorted lists % without duplicates. This implementation is only expected to work % for Item ground and either Set1 or Set2 ground. The "chk" suffix % is meant to remind you of memberchk/2, which also expects its % first argument to be ground. ord_selectchk(X, S, T) => % ord_memberchk(X, S) & \+ ord_memberchk(X, T). % % @author Richard O'Keefe ord_selectchk(Item, [X|Set1], [X|Set2]) :- X @< Item, !, ord_selectchk(Item, Set1, Set2). ord_selectchk(Item, [Item|Set1], Set1) :- ( Set1 == [] -> true ; Set1 = [Y|_] -> Item @< Y ). %! ord_memberchk(+Element, +OrdSet) is semidet. % % True if Element is a member of OrdSet, compared using ==. Note % that _enumerating_ elements of an ordered set can be done using % member/2. % % Some Prolog implementations also provide ord_member/2, with the % same semantics as ord_memberchk/2. We believe that having a % semidet ord_member/2 is unacceptably inconsistent with the *_chk % convention. Portable code should use ord_memberchk/2 or % member/2. % % @author Richard O'Keefe ord_memberchk(Item, [X1,X2,X3,X4|Xs]) :- !, compare(R4, Item, X4), ( R4 = (>) -> ord_memberchk(Item, Xs) ; R4 = (<) -> compare(R2, Item, X2), ( R2 = (>) -> Item == X3 ; R2 = (<) -> Item == X1 ;/* R2 = (=), Item == X2 */ true ) ;/* R4 = (=) */ true ). ord_memberchk(Item, [X1,X2|Xs]) :- !, compare(R2, Item, X2), ( R2 = (>) -> ord_memberchk(Item, Xs) ; R2 = (<) -> Item == X1 ;/* R2 = (=) */ true ). ord_memberchk(Item, [X1]) :- Item == X1. %! ord_subset(+Sub, +Super) is semidet. % % Is true if all elements of Sub are in Super ord_subset([], _). ord_subset([H1|T1], [H2|T2]) :- compare(Order, H1, H2), ord_subset_(Order, H1, T1, T2). ord_subset_(>, H1, T1, [H2|T2]) :- compare(Order, H1, H2), ord_subset_(Order, H1, T1, T2). ord_subset_(=, _, T1, T2) :- ord_subset(T1, T2). %! ord_subtract(+InOSet, +NotInOSet, -Diff) is det. % % Diff is the set holding all elements of InOSet that are not in % NotInOSet. ord_subtract([], _Not, Diff) => Diff = []. ord_subtract(List, [], Diff) => Diff = List. ord_subtract([H1|T1], L2, Diff) => diff21(L2, H1, T1, Diff). diff21([], H1, T1, [H1|T1]). diff21([H2|T2], H1, T1, Diff) :- compare(Order, H1, H2), diff3(Order, H1, T1, H2, T2, Diff). diff12([], _H2, _T2, []). diff12([H1|T1], H2, T2, Diff) :- compare(Order, H1, H2), diff3(Order, H1, T1, H2, T2, Diff). diff3(<, H1, T1, H2, T2, [H1|Diff]) :- diff12(T1, H2, T2, Diff). diff3(=, _H1, T1, _H2, T2, Diff) :- ord_subtract(T1, T2, Diff). diff3(>, H1, T1, _H2, T2, Diff) :- diff21(T2, H1, T1, Diff). %! ord_union(+SetOfSets, -Union) is det. % % True if Union is the union of all elements in the superset % SetOfSets. Each member of SetOfSets must be an ordered set, the % sets need not be ordered in any way. % % @author Copied from YAP, probably originally by Richard O'Keefe. ord_union([], Union) => Union = []. ord_union([Set|Sets], Union) => length([Set|Sets], NumberOfSets), ord_union_all(NumberOfSets, [Set|Sets], Union, []). ord_union_all(N, Sets0, Union, Sets) => ( N =:= 1 -> Sets0 = [Union|Sets] ; N =:= 2 -> Sets0 = [Set1,Set2|Sets], ord_union(Set1,Set2,Union) ; A is N>>1, Z is N-A, ord_union_all(A, Sets0, X, Sets1), ord_union_all(Z, Sets1, Y, Sets), ord_union(X, Y, Union) ). %! ord_union(+Set1, +Set2, -Union) is det. % % Union is the union of Set1 and Set2 ord_union([], Set2, Union) => Union = Set2. ord_union([H1|T1], L2, Union) => union2(L2, H1, T1, Union). union2([], H1, T1, Union) => Union = [H1|T1]. union2([H2|T2], H1, T1, Union) => compare(Order, H1, H2), union3(Order, H1, T1, H2, T2, Union). union3(<, H1, T1, H2, T2, Union) => Union = [H1|Union0], union2(T1, H2, T2, Union0). union3(=, H1, T1, _H2, T2, Union) => Union = [H1|Union0], ord_union(T1, T2, Union0). union3(>, H1, T1, H2, T2, Union) => Union = [H2|Union0], union2(T2, H1, T1, Union0). %! ord_union(+Set1, +Set2, -Union, -New) is det. % % True iff ord_union(Set1, Set2, Union) and % ord_subtract(Set2, Set1, New). ord_union([], Set2, Set2, Set2). ord_union([H|T], Set2, Union, New) :- ord_union_1(Set2, H, T, Union, New). ord_union_1([], H, T, [H|T], []). ord_union_1([H2|T2], H, T, Union, New) :- compare(Order, H, H2), ord_union(Order, H, T, H2, T2, Union, New). ord_union(<, H, T, H2, T2, [H|Union], New) :- ord_union_2(T, H2, T2, Union, New). ord_union(>, H, T, H2, T2, [H2|Union], [H2|New]) :- ord_union_1(T2, H, T, Union, New). ord_union(=, H, T, _, T2, [H|Union], New) :- ord_union(T, T2, Union, New). ord_union_2([], H2, T2, [H2|T2], [H2|T2]). ord_union_2([H|T], H2, T2, Union, New) :- compare(Order, H, H2), ord_union(Order, H, T, H2, T2, Union, New). %! ord_symdiff(+Set1, +Set2, ?Difference) is det. % % Is true when Difference is the symmetric difference of Set1 and % Set2. I.e., Difference contains all elements that are not in the % intersection of Set1 and Set2. The semantics is the same as the % sequence below (but the actual implementation requires only a % single scan). % % == % ord_union(Set1, Set2, Union), % ord_intersection(Set1, Set2, Intersection), % ord_subtract(Union, Intersection, Difference). % == % % For example: % % == % ?- ord_symdiff([1,2], [2,3], X). % X = [1,3]. % == ord_symdiff([], Set2, Set2). ord_symdiff([H1|T1], Set2, Difference) :- ord_symdiff(Set2, H1, T1, Difference). ord_symdiff([], H1, T1, [H1|T1]). ord_symdiff([H2|T2], H1, T1, Difference) :- compare(Order, H1, H2), ord_symdiff(Order, H1, T1, H2, T2, Difference). ord_symdiff(<, H1, Set1, H2, T2, [H1|Difference]) :- ord_symdiff(Set1, H2, T2, Difference). ord_symdiff(=, _, T1, _, T2, Difference) :- ord_symdiff(T1, T2, Difference). ord_symdiff(>, H1, T1, H2, Set2, [H2|Difference]) :- ord_symdiff(Set2, H1, T1, Difference).