________________________________________________________________________

This file is part of Logtalk <https://logtalk.org/>  
Copyright 1998-2021 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.
________________________________________________________________________


% start by loading the example:

| ?- logtalk_load(operators(loader)).
...


% operators declared inside an object are not visible outside:

| ?- double::(I double J).

Syntax error: Operator expected


% you must use instead functor notation:

| ?- double::double(I, J).

I = 1
J = 2 ;

I = 2
J = 4 ;

I = 3
J = 6 

yes


% operators also affect inputting of terms, enabling this example to work:

| ?- triple::read_from_file.

yes

| ?- triple::triple(I, J).

I = 1
J = 3 ;

I = 2
J = 6 ;

I = 3
J = 9 

yes


% local operators are used when reading terms (check the file "previous.txt"
% generated from the file "next.txt" by the object "reverse" by opening the
% files on a text editor):

| ?- reverse::reverse_file.

yes


% the "edge" operator on the "local.lgt" source file is not globally visible:

| ?- graph1::(N1 edge N2).
uncaught exception: error(syntax_error('user_input:10 (char:13) ) or operator expected'),read_term/3)


% you must use instead functor notation:

| ?- graph1::edge(N1, N2).

N1 = a
N2 = b ;

N1 = a
N2 = c ;

N1 = b
N2 = d ;

N1 = c
N2 = d

yes


| ?- graph1::path(a, d, Path).

Path = [a, b, d] ;

Path = [a, c, d] 

yes


% confirm that the "edge" operator have not became global:

| ?- current_op(P, T, edge).

no

