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 link in a web browser.


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

| ?- logtalk_load(sets(loader)).


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

| ?- logtalk_load(sets(tester)).


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 = []

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]

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]

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

 :- object(rainbow_colors,

    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_protocol.

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]

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


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