Implementing User Programs › Write a SUBSYS Program › Write a Subsystem Program in High-level Languages

Write a Subsystem Program in High-level Languages

The new format parameter list makes it possible to write both one-time programs using the &CALL command and subsystems in high-level languages, for example COBOL and PL/1.

There are several considerations for high-level languages:

• Always use a new format parameter list. The old format is incompatible with high-level languages.
• In COBOL, define the input parameters in the LINKAGE SECTION. COBOL cannot easily handle a variable number of parameters, but as long as the extra parameters on a specific call are not referred to (that is, the count is obeyed) then no problems should arise. Another technique may be used to access a variable number of parameters. The individual parameters are actually in contiguous storage. Thus, instead of individual parameters, just define the first one, as an array:

  LINKAGE SECTION.       
  ... other parms
  01 NCPC.      
  

  03 NCPCCNTPIC S9(9) COMP.      
  01 PARMS OCCURS 1.  ... actual count is NCPCCNT
  03 LENPIC S9(9) COMP.         
  03 VALPIC X(256).
  

  PROCEDURE DIVISION USING PLIST ... ... NCPC PARMS.
  

• Dope vectors are not set up for PL/1. Because of this, define all individual input parameters as FIXED BIN(31) and BASE a structure over them:

  DCL NCPN_            FIXED BIN(31),
      1  NCPNBASED     ADDR(NCPN_F),               
        3  NCPNPROC    CHAR(8),            
  

  The suggestion for COBOL regarding variable parameter counts applies to PL/1 also. Since the actual number of parameters is not part of the pseudo-array, a REFER structure cannot be used. Use PARMS(1) on the DCL.

  Do not compile with SUBSCRIPTRANGE in effect.

• Use the RETURN-CODE variable in COBOL to set the return code. Use CALL PLIRETC (code) IN PL/1.
• Use GOBACK rather than STOP RUN in COBOL to return.
• Both COBOL and PL/1 have large overheads for establishing the run-time environment. When repeated calls are necessary, these overheads can be excessive. Consult the relevant programmer's guide for details on callable interfaces that can perform a one-time build of this environment.