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The Waikato Environment for Knowledge Analysis (WEKA), a machine learning workbench. This version represents the developer version, the "bleeding edge" of development, you could say. New functionality gets added to this version.

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/*
 *   This program is free software: you can redistribute it and/or modify
 *   it under the terms of the GNU General Public License as published by
 *   the Free Software Foundation, either version 3 of the License, or
 *   (at your option) any later version.
 *
 *   This program is distributed in the hope that it will be useful,
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *   GNU General Public License for more details.
 *
 *   You should have received a copy of the GNU General Public License
 *   along with this program.  If not, see .
 */

/*
 *    VariableDeclarations.java
 *    Copyright (C) 2015 University of Waikato, Hamilton, New Zealand
 *
 */

package weka.core.expressionlanguage.core;

import java.io.Serializable;

/**
 * Interface to expose variables to a program.
 * 
 * It is deliberately kept very simple to give as little constraints
 * as possible to implementations.
 * 
 * There is an implied invariant here:

 * {@link #hasVariable(String)} == true ->
 * {@link #getVariable(String)} != null
 * 
 * {@link #hasVariable(String)} should be pure i.e. have no side effects.

 * Whereas {@link #getVariable(String)} may have side effects.

 * (This is useful for creating variables on the fly in {@link #getVariable(String)})
 * 
 * @author Benjamin Weber ( benweber at student dot ethz dot ch )
 * @version $Revision: 1000 $
 */
public interface VariableDeclarations extends Serializable {

  /**
   * Whether the variable is declared
   * 
   * @param name name of the variable being queried
   * @return whether the variable is declared
   */
  public boolean hasVariable(String name);
  
  /**
   * Tries to fetch a variable
   * 
   * Before a variable is fetched it should be checked whether it is declared
   * through {@link #hasVariable(String)}.
   * 
   * @param name name of the variable to be fetched
   * @return an AST (abstract syntax tree) node representing the variable
   */
  public Node getVariable(String name);
}