public class SL_IfNode extends ParseNode {
  // child 0: condition
  // child 1: 'then' block
  // child 2: 'else' block

  public int getType() { return G_IF; }
  public ParseNode interpret(SymbolTable st) 
    throws InterpretException, ReturnException {
      // write me 
      return null;
  }
}