jupyter: jupytext: text_representation: extension: .md format_name: markdown format_version: '1.3' jupytext_version: 1.16.7 kernelspec: display_name: Logtalk language: logtalk name: logtalk_kernel ---

<!--

This file is part of Logtalk https://logtalk.org/ SPDX-FileCopyrightText: 1998-2025 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. -->

parstructs

This example requires using ECLiPSe as the backend Prolog compiler. It illustrates using a ECLiPSe structure notation, which provides a solution for using structures with field names rather than positional arguments. This is accomplished by using a single parameter, instantiated to a structure, and by defining a set of predicates for accessing the individual parameters by a key (instead of using the Logtalk built-in parameter/2 method that indexes individual parameters by position). The access predicates are goal-expanded to the corresponding ECLiPSe structure built-in predicates.

Print Logtalk, Prolog backend, and kernel versions (if running as a notebook):

%versions

Start by loading the example:

logtalk_load(parstructs(loader)).

Backtrackable update of an individual parameter:

obj(Dict)::init([a-1, b-2, c-3]), (obj(Dict)::b_set(b, 9), obj(Dict)::get(b, B), write(b-B), nl, fail; obj(Dict)::get(b, B), write(b-B), nl).

Non-backtrackable update of an individual parameter:

obj(Dict)::init([a-1, b-2, c-3]), (obj(Dict)::nb_set(b, 9), obj(Dict)::get(b, B), write(b-B), nl, fail; obj(Dict)::get(b, B), write(b-B), nl).