code: public EvalError toEvalError(
          String msg, SimpleNode node, CallStack callstack  )
      {
          if ( Interpreter.DEBUG.get() )
              printStackTrace();
  
          if ( msg == null )
              msg = "";
          else
              msg += ": ";
          return new EvalError( msg + this.getMessage(), node, callstack, this );
      }
docs: Re-throw as an eval error, prefixing msg to the message and specifying
  the node.  If a node already exists the addNode is ignored.
  @see #setNode( bsh.SimpleNode )
  <p>
  @param msg may be null for no additional message.