code: ///////////////////////////////////////////////////////////////////////////////
  // For information as to what this class does, see the Javadoc, below.       //
  // Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006,       //
  // 2007, 2008, 2009, 2010, 2014, 2015 by Peter Spirtes, Richard Scheines, Joseph   //
  // Ramsey, and Clark Glymour.                                                //
  //                                                                           //
  // 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 2 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, write to the Free Software               //
  // Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA //
  ///////////////////////////////////////////////////////////////////////////////
  
  package edu.cmu.tetrad.calculator.expression;
  
  import edu.cmu.tetrad.util.TetradSerializable;
  import org.apache.commons.math3.distribution.IntegerDistribution;
  import org.apache.commons.math3.distribution.RealDistribution;
  
  import java.util.List;
  
  /**
   * Represents a mathematical expression. Used in the Calculator and
   * the Generalized Sem model.
   * </p>
   * Note that expressions form trees. Each expression has a (possibly
   * empty) list of children.
   *
   * @author Tyler Gibson
   */
  public interface Expression extends TetradSerializable {
      long serialVersionUID = 23L;
  
      /**
       * Evaluates the expression using the given context
       */
      double evaluate(Context context);
  
      /**
       * @return the token for this expression=="+".
       */
      String getToken();
  
      /**
       * @return the position, infix or not.
       */
      ExpressionDescriptor.Position getPosition();
  
      /**
       * @return the sub expressions of this expression.
       */
      List<Expression> getExpressions();
  
      /**
       */
      RealDistribution getRealDistribution(Context context);
  
      /**
       */
      IntegerDistribution getIntegerDistribution(Context context);
  
  }
  
  
  
  