CLIST

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. The term CLIST is also used for command lists written by users of NetView.
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 programs.
 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