DEBUG_LINE
     Returns the line number of the current break point.  This built-in is
     used in user-written debugging programs.  If you do not write your own
     debugging program, you can use the debugger provided with DECTPU,
     located in SYS$SHARE:TPU$DEBUG.TPU.
  Syntax
     integer := DEBUG_LINE
  Parameters
     none
        Related Topics
     SET(DEBUG)