Description

   This user-written routine is invoked by the TPU built-in
   procedure CALL_USER. The built-in procedure CALL_USER passes
   three parameters to this routine. These parameters are then
   passed to the appropriate part of your application to be used
   as specified. (For example, they can be used as operands in a
   calculation within a Fortran program.) Using the string routines
   provided by the Run-Time Library, your application fills in the
   stringout parameter in the call-user routine, which returns the
   stringout value to the built-in procedure CALL_USER.

   The description of the built-in procedure CALL_USER in the DEC
   Text Processing Utility Reference Manual shows an example of a
   BASIC program that is a call-user routine.