be83a4a309
git-svn-id: https://yap.svn.sf.net/svnroot/yap/trunk@1120 b08c6af1-5177-4d33-ba66-4b1c6b8b522a
302 lines
11 KiB
Java
302 lines
11 KiB
Java
//tabstop=4
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//*****************************************************************************/
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// Project: jpl
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//
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// File: $Id: Variable.java,v 1.1 2004-08-27 20:27:56 vsc Exp $
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// Date: $Date: 2004-08-27 20:27:56 $
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// Author: Fred Dushin <fadushin@syr.edu>
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//
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//
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// Description:
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//
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//
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// -------------------------------------------------------------------------
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// Copyright (c) 2004 Paul Singleton
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// Copyright (c) 1998 Fred Dushin
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// All rights reserved.
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//
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// This library is free software; you can redistribute it and/or
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// modify it under the terms of the GNU Library Public License
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// as published by the Free Software Foundation; either version 2
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// of the License, or (at your option) any later version.
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//
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// This library is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU Library Public License for more details.
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//*****************************************************************************/
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package jpl;
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import java.util.Iterator;
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import java.util.Map;
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import jpl.fli.Prolog;
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import jpl.fli.term_t;
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//----------------------------------------------------------------------/
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// Variable
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/**
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* This class supports Java representations of Prolog variables.<p>
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*
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* A jpl.Variable instance is equivalent to a variable in a fragment of Prolog source text:
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* it is *not* a "live" variable within a Prolog stack or heap.
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* A corresponding Prolog variable is created only upon opening
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* a Query whose goal refers to a Variable (and then only temporarily).
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*
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* <hr><i>
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* Copyright (C) 2004 Paul Singleton<p>
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* Copyright (C) 1998 Fred Dushin<p>
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*
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* This library is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Library Public License
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* as published by the Free Software Foundation; either version 2
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* of the License, or (at your option) any later version.<p>
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*
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* This library is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU Library Public License for more details.<p>
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* </i><hr>
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* @author Fred Dushin <fadushin@syr.edu>
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* @version $Revision: 1.1 $
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*/
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// Implementation notes:
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//
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//----------------------------------------------------------------------/
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public class Variable extends Term {
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//==================================================================/
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// Attributes
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//==================================================================/
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private static long n = 0; // the integral part of the next automatic variable name to be allocated
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public final String name; // the name of this Variable
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protected transient term_t term_ = null; // defined between Query.open() and Query.get2()
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protected transient int index; // only used by (redundant?)
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//==================================================================/
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// Constructors
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//==================================================================/
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/**
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* Create a new Variable with 'name' (which must not be null or ""),
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* and may one day be constrained to comply with traditional Prolog syntax.
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*
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* @param name the source name of this Variable
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*/
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public Variable(String name) {
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if (name == null) {
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throw new JPLException("constructor jpl.Variable(name): name cannot be null");
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}
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if (!isValidName(name)) {
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throw new JPLException("constructor jpl.Variable(name): name cannot be empty String");
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}
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this.name = name;
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}
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//==================================================================/
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// Constructors (deprecated)
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//==================================================================/
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/**
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* Create a new Variable with new sequential name of the form "_261".
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*
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* @deprecated use Variable(String name) instead
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*/
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public Variable() {
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this.name = "_" + Long.toString(n++); // e.g. _0, _1 etc.
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}
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//==================================================================/
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// Methods (common)
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//==================================================================/
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/**
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* returns the lexical name of this Variable
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*
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* @return the lexical name of this Variable
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*/
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public final String name() {
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return this.name;
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}
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/**
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* Returns a Prolog source text representation of this Variable
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*
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* @return a Prolog source text representation of this Variable
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*/
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public String toString() {
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return this.name;
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}
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/**
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* A Variable is equal to another if their names are the same and they are not anonymous.
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*
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* @param obj The Object to compare.
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* @return true if the Object is a Variable and the above condition apply.
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*/
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public final boolean equals(Object obj) {
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return obj instanceof Variable && !this.name.equals("_") && this.name.equals(((Variable) obj).name);
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}
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public final int type() {
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return Prolog.VARIABLE;
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}
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public String typeName() {
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return "Variable";
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}
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//==================================================================/
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// Methods (private)
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//==================================================================/
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/**
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* Tests the lexical validity of s as a variable's name
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*
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* @return the lexical validity of s as a variable's name
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* @deprecated
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*/
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private boolean isValidName(String s) {
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if (s == null) {
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throw new java.lang.NullPointerException(); // JPL won't call it this way
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}
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int len = s.length();
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if (len == 0) {
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throw new JPLException("invalid variable name");
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}
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char c = s.charAt(0);
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if (!(c == '_' || c >= 'A' && c <= 'Z')) {
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return false;
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}
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for (int i = 1; i < len; i++) {
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c = s.charAt(i);
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if (!(c == '_' || c >= 'A' && c <= 'Z' || c >= 'a' && c <= 'z' || c >= '0' && c <= '9')) {
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return false;
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}
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}
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return true;
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}
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//==================================================================/
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// Methods (deprecated)
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//==================================================================/
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/**
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* The (nonexistent) args of this Variable
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*
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* @return the (nonexistent) args of this Variable
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* @deprecated
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*/
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public Term[] args() {
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return new Term[] {
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};
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}
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/**
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* Returns a debug-friendly String representation of an Atom.
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*
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* @return a debug-friendly String representation of an Atom
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* @deprecated
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*/
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public String debugString() {
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return "(Variable " + toString() + ")";
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}
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//==================================================================/
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// Converting JPL Terms to Prolog terms
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//==================================================================/
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/**
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* To put a Variable, we must check whether a (non-anonymous) variable with the same name
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* has already been put in the Term. If one has, then the corresponding Prolog variable has
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* been stashed in the varnames_to_vars Map, keyed by the Variable name, so we can look
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* it up and reuse it (this way, the sharing of variables in the Prolog term
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* reflects the sharing of Variable names in the Term.
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* Otherwise, if this Variable name has not
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* already been seen in the Term, then we put a new Prolog variable and add it into the Map
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* (keyed by this Variable name).
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*
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* @param varnames_to_vars A Map from variable names to Prolog variables.
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* @param term A (previously created) term_t which is to be
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* set to a (new or reused) Prolog variable.
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*/
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protected final void put(Map varnames_to_vars, term_t term) {
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term_t var;
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// if this var is anonymous or as yet unseen, put a new Prolog variable
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if (this.name.equals("_") || (var = (term_t) varnames_to_vars.get(this.name)) == null) {
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this.term_ = term;
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this.index = varnames_to_vars.size(); // i.e. first var in is #0 etc.
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Prolog.put_variable(term);
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if (!this.name.equals("_")) {
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varnames_to_vars.put(this.name, term);
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}
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} else {
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this.term_ = var;
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Prolog.put_term(term, var);
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}
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}
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//==================================================================/
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// Converting Prolog terms to JPL Terms
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//==================================================================/
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/**
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* Converts a term_t (known to refer to a Prolog variable) to a Variable.
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* If the variable has already been seen (and hence converted),
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* return its corresponding Variable from the map,
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* else create a new Variable, stash it in the map (keyed by the Prolog variable),
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* and return it.
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*
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* @param vars_to_Vars a map from Prolog to JPL variables
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* @param var The term_t (known to be a variable) to convert
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* @return A new or reused Variable
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*/
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protected static Term getTerm(Map vars_to_Vars, term_t var) {
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for (Iterator i = vars_to_Vars.keySet().iterator(); i.hasNext();) {
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term_t varX = (term_t) i.next(); // a previously seen Prolog variable
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if (Prolog.compare(varX, var) == 0) { // identical Prolog variables?
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return (Term) vars_to_Vars.get(varX); // return the associated JPL Variable
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}
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}
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// otherwise, the Prolog variable in term has not been seen before
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Variable Var = new Variable(); // allocate a new (sequentially named) Variable to represent it
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Var.term_ = var; // this should become redundant...
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vars_to_Vars.put(var, Var); // use Hashtable(var,null), but only need set(var)
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return Var;
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}
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//==================================================================/
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// Computing Substitutions
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//==================================================================/
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/**
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* If this Variable instance is not an anonymous or (in dont-tell-me mode) a dont-tell-me variable, and its binding is not already in the varnames_to_Terms Map,
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* put the result of converting the term_t to which this variable
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* has been unified to a Term in the Map, keyed on this Variable's name.
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*
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* @param varnames_to_Terms A Map of bindings from variable names to JPL Terms.
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* @param vars_to_Vars A Map from Prolog variables to JPL Variables.
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*/
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protected final void getSubst(Map varnames_to_Terms, Map vars_to_Vars) {
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// NB a Variable.name cannot be "" i.e. of 0 length
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// if (!(this.name.charAt(0) == '_') && varnames_to_Terms.get(this.name) == null) {
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if (tellThem() && varnames_to_Terms.get(this.name) == null) {
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varnames_to_Terms.put(this.name, Term.getTerm(vars_to_Vars, this.term_));
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}
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}
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// whether, according to prevailing policy and theis Variable's name,
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// any binding should be returned
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// (yes, unless it's anonymous or we're in dont-tell-me mode and its a dont-tell-me variable)
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private final boolean tellThem() {
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return !(this.name.equals("_") || jpl.JPL.modeDontTellMe && this.name.charAt(0) == '_');
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// return !this.name.equals("_");
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}
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}
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//345678901234567890123456789012346578901234567890123456789012345678901234567890
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