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This file is part of Logtalk https://logtalk.org/ SPDX-FileCopyrightText: 1998-2023 Paulo Moura <pmoura@logtalk.org> SPDX-License-Identifier: Apache-2.0

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.

sets

This library provides a set protocol and two implementations of this protocol using ordered lists, one of them a parametric object that takes the type of the set elements as a parameter. Although representing sets as ordered lists is a common representation, is best practice to regard sets as opaque terms and only access them using the library predicates.

API documentation

Open the [../../docs/library_index.html#sets](../../docs/library_index.html#sets) link in a web browser.

Loading

To load all entities in this library, load the loader.lgt file:

| ?- logtalk_load(sets(loader)).

Testing

To test this library predicates, load the tester.lgt file:

| ?- logtalk_load(sets(tester)).

Usage

First, select a set implementation. Use the set(Type) object if you want to type-check the set elements. Otherwise, use the set object.

To create a new set, you can use the new/1 predicate. For example:

| ?- set::new(Set). Set = [] yes

You can also create a new set with all unique elements from a list of terms by using the as_set/2 predicate. For example:

| ?- set::as_set([1,3,2,1,2], Set). Set = [1, 2, 3] yes

Predicates are provided for the most common set operations. For example:

| ?- set::( as_set([1,3,2,1,2], Set1), as_set([7,4,2,5,1], Set2), intersection(Set1, Set2, Intersection), symdiff(Set1, Set2, Difference) ). Set1 = [1, 2, 3], Set2 = [1, 2, 4, 5, 7], Intersection = [1, 2], Difference = [3, 4, 5, 7] yes

When working with a custom type of set elements, the corresponding object must implement the comparingp protocol. For example:

:- object(rainbow_colors,
        implements(comparingp)).

        order(red,    1).
        order(orange, 2).
        order(yellow, 3).
        order(green,  4).
        order(blue,   5).
        order(indigo, 6).
        order(violet, 7).

        Color1 < Color2 :-
                order(Color1, N1),
                order(Color2, N2),
                {N1 < N2}.

        Color1 =< Color2 :-
                order(Color1, N1),
                order(Color2, N2),
                {N1 =< N2}.

        ...

:- end_object.

We can then use this object with the set/1 parametric object. For example:

| ?- set(rainbow_colors)::as_set([blue, yellow, violet], Set). Set = [yellow, blue, violet] yes

For details on these and other provided predicates, consult the library API documentation.

Credits

Some predicates adapted from code authored by Richard O'Keefe.