# `dictionaries`

This library provides a dictionary (also known as associative array, map, or symbol table) protocol and binary tree, AVL tree, and Red–Black tree implementations. The different representations of a dictionary should be regarded as opaque terms and only accessed using the library predicates.

## API documentation

Open the ../../docs/library_index.html#dictionaries link in a web browser.

## Loading

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

    | ?- logtalk_load(dictionaries(loader)).

## Testing

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

    | ?- logtalk_load(dictionaries(tester)).

## Usage

First, select the dictionary implementation that you want to use. For cases where the number of elements is relatively small and performance is not critical, `bintree` can be a good choice. For other cases, `avltree` or `rbtree` are likely better choices. If you want to compare the performance of the implementations, either define an object alias or use a `uses/2` directive so that you can switch between implementations by simply changing the alias definition or the first argument of the directive. Note that you can switch between implementations at runtime without code changes by using a parameter variable in the first argument of a `uses/2` directive.

Dictionary keys should preferably be ground terms. If the keys contain variables, the user must ensure that any instantiation of those variables when calling this library predicates will not affect the key ordering.

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

    | ?- avltree::new(Dictionary).
    Dictionary = ...
    yes

You can also create a new dictionary from a list of key-value pairs by using the `as_dictionary/2` predicate. For example:

    | ?- avltree::as_dictionary([a-1,c-3,b-2], Dictionary).
    Dictionary = ...
    yes

Several predicates are provided for inserting key-value pairs, lookup key-value pairs updating the value associated with a key, and deleting key-value pairs. For example:

    | ?- avltree::(
            new(Dictionary0),
            insert(Dictionary0, a, 1, Dictionary1),
            update(Dictionary1, a, 2, Dictionary2),
            lookup(a, Value, Dictionary2)
        ).
    Dictionary0 = ...,
    Dictionary1 = ...,
    Dictionary2 = ...,
    Value = 2
    yes

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

## Credits

The AVL tree implementation is an adaptation to Logtalk of the `assoc` SWI-Prolog library authored by R.A.O’Keefe, L.Damas, V.S.Costa, Glenn Burgess, Jiri Spitz, and Jan Wielemaker. Additional predicates authored by Paulo Moura.

The Red–Black tree implementation is an adaptation to Logtalk of the `rbtrees` Prolog library authored by Vitor Santos Costa.