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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.

To load this example and for sample queries, please see the SCRIPT.txt file.

This folder contains a Logtalk version of a GNU Prolog/CX unit example, a simple dictionary implementation using a list of key-value pairs:

:- unit(dict(ST)).

dict(ST).

lookup(KEY, VALUE) :- ST=[KEY=VALUE|_].
lookup(KEY, VALUE) :- ST=[_|STx], dict(STx) :> lookup(KEY, VALUE).

For a description of GNU Prolog/CX, see:

@inproceedings{inproceedings,
        author = {Abreu, Salvador and Diaz, Daniel},
        year = {2003},
        month = {12},
        pages = {128-147},
        title = {Objective: In Minimum Context},
        isbn = {978-3-540-20642-2},
        doi = {10.1007/978-3-540-24599-5_10}
}

The code example is also mentioned in the following paper:

@incollection{pmoura11a,
        author = {Paulo Moura},
        booktitle = {Applications of Declarative Programming and Knowledge Management},
        title = {Programming Patterns for Logtalk Parametric Objects},
        editor = "Salvador Abreu and Dietmar Seipel",
        series = "Lecture Notes in Artificial Intelligence",
        volume = "6547",
        publisher = "Springer-Verlag",
        address = "Berlin Heidelberg",
        pages = "52--69",
        month = apr,
        year = 2011
}

The Logtalk compiler optimizes message-sending calls sent from an object to itself (as found in the definition of the lookup/2 predicate in this example), removing the message sending overhead, and thus providing the same performance as a local predicate call.