.. _library_sets:

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, the best practice is 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.