Variable.java 

// FILE. . . . . d:/hak/hlt/src/hlt/fot/Variable.java
// EDIT BY . . . Hassan Ait-Kaci
// ON MACHINE. . Hak-Laptop
// STARTED ON. . Sat Jul 14 07:24:10 2018

package hlt.fot;
This is a class for variables that may appear in first-order terms. It implements the interface FirstOrderTerm.

See also:  FirstOrderTerm
Copyright:  © by the author
Author:  Hassan Aït-Kaci
Version:  Last modified on Thu Aug 16 05:50:56 2018 by hak 



import java.util.HashMap;
import java.util.ArrayList;

public class Variable implements FirstOrderTerm
{
  /* ************************************************************************ */
  // Fields and accessors:
  /* ************************************************************************ */

  private String name;
  private boolean isAnonymous = false;

  public String name ()
  {
    return name;
  }

  public boolean isAnonymous ()
  {
    return isAnonymous;
  }

  /* ************************************************************************ */
  // Constructors: they are all private to ensure that only this class
  // may use them; the public method getVariable(String) is the one to
  // use to access a registered variable or create it and register it;
  /* ************************************************************************ */

  private Variable ()
  {
    this(anonymousVariableName(),true);
  }

  private Variable (String name)
  {
    this.name = name;
    registeredVariableNames.add(name);
    registeredVariableTable.put(name,this);
  }

  private Variable (String name, boolean isAnonymous)
  {
    this(name);
    this.isAnonymous = isAnonymous;
  }

  /* ************************************************************************ */
  // Methods:
  /* ************************************************************************ */
Returns true. This implements the FirstOrderTerm interface's method identifying this as a variable. 


  final public boolean isVariable ()
  {
    return true;
  }
Returns true iff this variable occurs in the specified term. 


  public boolean occursIn (FirstOrderTerm term)
  {
    if (term.isVariable())
      return this == ((Variable)term).deref();

    FirstOrderTermStructure t = (FirstOrderTermStructure)term;

    for (int i = 1; i <= t.functor().arity(); i++)
      if (this.occursIn(t.argument(i)))
	return true;

    return false;
  }

  /* ************************************************************************ */
  // Static structures and methods:
  /* ************************************************************************ */
This is a String → Variable association table where all variables are uniquely represented and identified by their names. 


  public static HashMap registeredVariableTable = new HashMap();
This is an ordered list of the names of all the registered variables in the order of creation (upon initial registration). 


  public static ArrayList registeredVariableNames = new ArrayList();
Returns the variable uniquely associated to this name if it exists, or creates it and returns it. 


  public static Variable getVariable (String name)
  {
    Variable variable = (Variable)registeredVariableTable.get(name);

    if (variable == null)
      variable = new Variable(name);

    return variable;
  }
This is the count of anomymous variables. 


  private static int anomymousVarCount = 0;
Erases all existing variables. 


  public static void resetRegisteredVariables ()
  {
    registeredVariableNames.clear();
    registeredVariableTable.clear();
    anomymousVarCount = 0;
  }

  private static String anonymousVariableName ()
  {
    return "_"+(anomymousVarCount++);
  }
Returns a new anonymous variable. 


  public static Variable anonymousVariable ()
  {
    return new Variable(anonymousVariableName(),true);
  }

  /* ************************************************************************ */
  // VARIABLE DEREFERENCING & BINDING
  /* ************************************************************************ */

  private FirstOrderTerm deref = this;

  public FirstOrderTerm deref ()
  {
    if (deref == this)
      return this;

    if (deref.isVariable())
      return ((Variable)deref).deref();

    return deref;
  }

  public boolean isBound ()
  {
    return deref() != this;
  }

  public boolean isUnbound ()
  {
    return deref() == this;
  }

  public void bind (FirstOrderTerm term)
  {
    deref = term;
  }

  /* ************************************************************************ */
  // STRING FORM
  /* ************************************************************************ */
Returns the string form of this variable. 


  public String toString ()
  {
    return name();
  }
Returns the string form of this variable taking into account its eventual binding. Overrrides the equivalent but less efficient default in FirstOrderTerm. 


  public String derefToString ()
  {
    FirstOrderTerm term = deref();

    if (term.isVariable())
      return term.toString();

    return term.derefToString();
  }

  /* ************************************************************************ */
  // EQUALITY
  /* ************************************************************************ */
Returns true if the specified term is this variable. Because a variable is uniquely represented, they must be the same individual. 


  public boolean equal (FirstOrderTerm term)
  {
    return this == term;
  }

}

This file was generated on Sat Aug 25 07:59:54 CEST 2018 from file Variable.java
by the hlt.language.tools.Hilite Java tool written by Hassan Aït-Kaci