CLIST

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CLIST (Command List) (pronounced "C-List") is a procedural programming language for TSO in MVS systems. It originated in OS/360 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 (or "CLIST" for short) can take the form of a simple list of commands to be executed in strict sequence (like a DOS batch file (*.bat) file). However, CLIST also features If-Then-Else logic as well as loop constructs.

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 background (by running JCL which executes the TSO control program (IKJEFT01)). TSO I/O screens and menus using ISPF dialog services can be displayed by CLISTs.

Compare the function of CLIST with that provided by REXX.

Example program:

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

Note:- Here PROC is treated as a separate routine.