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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 example contains simple meta-interpreters for pure Prolog encapsulated in Logtalk categories:

[115, 111, 108, 118, 101, 114]

simple meta-interpreter for pure Prolog

[112, 114, 111, 111, 102, 95, 116, 114, 101, 101]

simple meta-interpreter for pure Prolog returning the proof tree for successful queries

[116, 114, 97, 99, 101, 114]

simple meta-interpreter for pure Prolog that traces proof construction

[99, 111, 117, 110, 116, 101, 114]

simple meta-interpreter for counting the number of resolution steps when proving a goal

To use a meta-interpreter with an object, simply import the corresponding category.

Defining meta-interpreters as categories allows the use of the built-in predicate clause/2 to access the clauses of object predicates without forcing these predicates to be declared public or protected. Within a category, calls to the built-in predicate clause/2 retrieve clauses in "this", i.e. in the database of the object importing the category.

Counting the number of resolution steps can be applied to a naive implementation of list reversing for computing LIPS (logical inferences per second). Reversing a list of 30 elements is know to take 496 resolution steps. Therefore, if T is the time in seconds that a system takes to repeat N times this list reversal operation, then:

LIPS = (496 * N) / T

The value of N should be large enough to smooth out any timing fluctuations. Note that this benchmark is mainly of historical significance. It can be traced to a David Warren's paper about the Edinburgh Prolog compiler.