private String indentString(){
  StringBuffer sb=new StringBuffer();
  for (int i=0; i < indent; ++i) {
    sb.append("  ");
  }
  return sb.toString();
}

private String indentString ( ) { StringBuffer sb = new StringBuffer ( ) ; for ( int i = 0 ; i < indent ; ++ i ) { sb . append ( "  " ) ; } return sb . toString ( ) ; }
indent child nodes to help visually identify the structure of the ast .
