1 EXTERNAL
 The EXTERNAL  statement  declares  constants,  variables,  functions,  and
 subroutines  external  to  your  program.  You can describe parameters for
 external functions and subroutines.

 Examples:

 EXTERNAL INTEGER CONSTANT SS$_NORMAL
 EXTERNAL INTEGER Event_flag
 EXTERNAL INTEGER FUNCTION Rect_area (REAL BY REF, REAL BY REF)
 EXTERNAL SUB File_open (LONG BY VALUE, STRING)

2 Syntax

 External Constants:

     EXTERNAL data-type CONSTANT const-name,...

 External Variables:

     EXTERNAL data-type unsubs-var-name,...

 External Functions:

     EXTERNAL data-type FUNCTION {func-name [pass-mech] [([external-
              param],...)]}

 External Subroutines:

     EXTERNAL SUB {sub-name [pass-mech] [([external-param],...)]},...

     external-param: [OPTIONAL] [ data-type ] [ DIM ([,]...) ] [ pass-mech]

       pass-mech:  { BY DESC  }
                   { BY REF   }
                   { BY VALUE }