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1   /*
2    * #%L
3    * prolobjectlink-jpi
4    * %%
5    * Copyright (C) 2019 Prolobjectlink Project
6    * %%
7    * Permission is hereby granted, free of charge, to any person obtaining a copy
8    * of this software and associated documentation files (the "Software"), to deal
9    * in the Software without restriction, including without limitation the rights
10   * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
11   * copies of the Software, and to permit persons to whom the Software is
12   * furnished to do so, subject to the following conditions:
13   * 
14   * The above copyright notice and this permission notice shall be included in
15   * all copies or substantial portions of the Software.
16   * 
17   * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
18   * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
19   * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
20   * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
21   * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
22   * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
23   * THE SOFTWARE.
24   * #L%
25   */
26  package io.github.prolobjectlink.prolog;
27  
28  /**
29   * <p>
30   * Represent structured prolog compound term. Prolog structures consist in a
31   * relation the functor (structure name) and arguments enclosed between
32   * parenthesis.
33   * </p>
34   * <p>
35   * The Prolog Provider is the mechanism to create a new Prolog structures
36   * invoking {@link PrologProvider#newStructure(String, PrologTerm...)}.
37   * </p>
38   * <p>
39   * Two structures are equals if and only if are structure and have equals
40   * functor and arguments. Structures terms unify only with same functor and
41   * arguments structures, with free variable or with with structures where your
42   * arguments unify if they have the same functor and arity.
43   * </p>
44   * <p>
45   * Structures have a special property named arity that means the number of
46   * arguments present in the structure.
47   * </p>
48   * <p>
49   * There are two special structures term. They are expressions (Two arguments
50   * structure term with operator functor) and atoms (functor with zero
51   * arguments). For the first special case must be used
52   * {@link PrologProvider#newStructure(PrologTerm, String, PrologTerm)}
53   * specifying operands like arguments and operator like functor. For the second
54   * special case must be used {@link PrologProvider#newAtom(String)} specifying
55   * functor only.
56   * </p>
57   * 
58   * @author Jose Zalacain
59   * @since 1.0
60   */
61  public interface PrologStructure extends PrologTerm {
62  
63  	/**
64  	 * Return the operator (structure functor) of the current term if the current
65  	 * term is an evalueble structure (expression). This method is equivalent to
66  	 * invoke #{@link #getFunctor()}
67  	 * 
68  	 * @return return the operator of the current term if the current term is an
69  	 *         (expression).
70  	 * @since 1.0
71  	 */
72  	public String getOperator();
73  
74  	/**
75  	 * Return the left operand of the current term if the current term is an
76  	 * evalueble structure (expression). This method is equivalent to invoke
77  	 * {@link #getArgument(int)} with integer parameter equals to zero.
78  	 * 
79  	 * @return return the left operand of the current term if the current term is an
80  	 *         expression.
81  	 * @since 1.0
82  	 */
83  	public PrologTerm getLeft();
84  
85  	/**
86  	 * Return the right operand of the current term if the current term is an
87  	 * evalueble structure (expression). This method is equivalent to invoke
88  	 * {@link #getArgument(int)} with integer parameter equals to one.
89  	 * 
90  	 * @return return the right operand of the current term if the current term is
91  	 *         an expression.
92  	 * @since 1.0
93  	 */
94  	public PrologTerm getRight();
95  
96  }