/**
  * Copyright (c): Uwe Schmidt, FH Wedel
  *
  * You may study, modify and distribute this source code
  * FOR NON-COMMERCIAL PURPOSES ONLY.
  * This copyright message has to remain unchanged.
  *
  * Note that this document is provided 'as is',
  * WITHOUT WARRANTY of any kind either expressed or implied.
  */

abstract
class BinaryExpr extends Expr {

  // die Operanden

  protected
  Expr left;

  protected
  Expr right;

  //--------------------

  // der Konstruktor ist protected
  // da er nur von Subklassen aus aufgerufen wird

  protected
  BinaryExpr(Expr left, Expr right) {
    this.left  = left;
    this.right = right;
  }

  public Object eval() {
      Object v1 = left.eval();
      Object v2 = right.eval();
      return
        op2(v1, v2);
  }

  public
  String toString() {
    return
      "(" +
      left.toString() +
      " " + op2ToString() + " " +
      right.toString() +
      ")";
  }

  // Schablonenmethoden fuer 2-stellige Operationen

  protected abstract Object op2(Object v1, Object v2);
  protected abstract String op2ToString();
}