CLIST

CLIST (Command List; pronounced "C-List") is a procedural programming language for Time Sharing Option (TSO) in SVS and MVS systems. It originated in OS/360¹ Release 20 and has assumed a secondary role since the availability of Rexx in TSO/E Version 2. In its basic form, a CLIST program is a list of commands to be executed in strict sequence. OS/VS2 R3.6 (MVS) added If-Then-Else logic and loop constructs to CLIST.² The term CLIST is also used for command lists written by users of NetView.³

CLIST is an interpreted language. That is, the computer must translate a CLIST every time the program is executed. CLISTs therefore tend to be slower than programs written in compiled languages such as COBOL, FORTRAN, or PL/1. (A program written in a compiled language is translated once to create a "load module" or executable.)

CLIST can read/write MVS files and read/write from/to a TSO terminal. It can read parameters from the caller and also features a function to hold global variables and pass them between CLISTs. A CLIST can also call an MVS application program (written in COBOL or PL/I, for example). CLISTs can be run in backgroundⁱⁱⁱⁱⁱ. CLISTs can display TSO I/O screens and menus by using ISPF dialog services.

Compare the function of CLIST with that provided by REXX.

 PROC 0
 WRITE HELLO WORLD!

Adding If-Then-Else logic:

   /********************************************************************/
   /*  MULTI-LINGUAL "HELLO WORLD" PROGRAM.                            */
   /*                                                                  */
   /*  THIS CLIST, STORED AS USERID.TSO.CLIST(TEST), CAN BE INVOKED    */
   /*  FROM THE ISPF COMMAND LINE AS SHOWN IN THE FOLLOWING EXAMPLE:   */
   /*                                                                  */
   /*     COMMAND ===> TSO TEST SPANISH                                */
   /*                                                                  */
   /********************************************************************/
   PROC 1 LANGUAGE
     IF &LANGUAGE = SPANISH THEN +
        WRITE HOLA, MUNDO
     ELSE IF &LANGUAGE = FRENCH THEN +
        WRITE BONJOUR, MONDE
     ELSE +
        WRITE HELLO, WORLD
   EXIT