RPG Language
HLL for Business Applications
Coding in RPG (Report Program Generator) has been taking place since 1959. Of course, the language has changed dramatcially over the last half century. RPG has had to change in order to keep pace with the changing demands of midrange system application requirements. From IBM S/3, to S/34, through the S/38 and S/36 years, and through the AS/400, iSeries machines, and now the Power i products, RPG has been the overwhelming language of choice for application development on the IBM midrange platform.
The language began as a fixed-format columnar code for report writing and has morphed into a free-format language of tremendous scope. As of Release 7.1 of the i OS, new operations after TR7, RPG is no longer framed by fixed-format instructions, or definitions.
Introduction and RPG II
IBM introduced RPG to the business world in 1959. In 1969, RPG II made its debut. (Intro to RPG) It was a staple on IBM's S/3 platforms.
*================================================================
* This is a sample of RPG II code
*================================================================
*
C 21NU2 SETON 62
C 21N62 U2 GOTO END
C 21 EMPNOCHAINMASTER 99
C 21 ADD 1 CNT 30
C 21 ADD CSALE TCSALE 80
C 21 ADD CGROSS TCGROS 80
C 21 ADD CPD TCPD 80
C 21 ADD CCL TCCL 80
C 21 ADD CRES TCRES 80
C 21 ADD YSALE TYSALE 80
C 21 ADD YGROSS TYGROS 80
C 21 ADD YPD TYPD 80
C 21 ADD YCL TYCL 80
C 21 ADD YRES TYRES 80
C 21 Z-ADDCPERG CPERG1 52H
C 21 Z-ADDYPERG YPERG1 52H
C END TAG
RPG III
In 1979, RPG III offered major enhancement. IBM's S/38 RPG compilers were still dependent on fixed-column code. However, logic operations (op codes) made the language more versatile. As a common practice, programmers abandoned using left-hand indicators.
*----------------------------------------------------------------
* Put the line of text in the window data structure
*----------------------------------------------------------------
B1 C DOW *IN26 = *OFF
<--- C EXSR @WLIN
C READ INPUT 25
B2 C IF *IN25 = *ON
C OR FMTID = 'FMT'
C EVAL *IN26 = *ON
B3 C IF X < RCDS
C EVAL RCDS = X
E3 C ENDIF
E2 C ENDIF
B2 C IF *IN25 = *OFF
C AND X <= RCDS
C AND FMTID <> 'FMT'
C EVAL #LRCD = NMBR1
E2 C ENDIF
*----------------------------------------------------------------
B2 C IF X > RCDS
C MOVE '+' BTMBAR
C EVAL *IN26 = *ON
E2 C ENDIF
E1 C ENDDO
RPG IV and ILE
In 1994, RPG compilers became a part of the Integrated Language Environment (ILE) which allowed RPG programs to use procedures. Free format code, arrived in 2001, so RPG calculations were no longer dependent on fixed-column code. Logic loops and in-line case structures became common and programmers could indent the code to make the logic clearer. Binding and activation groups added a degree of complexity to RPG application development but offered a tremendous degree of functionality to RPG applications.
DOU %eof(SC0320DF);
READC SC0320S1;
listAction = *off;
IF NOT %eof(SC0320DF);
IF Z$OPT <> *BLANK;
listAction = *ON;
thisOption = %triml(z$opt);
ThisFormat = fmtnam;
ThisPgm = prgnam;
GetOption(Thispgm:ThisFormat:thisOption:macro:authl);
SELECT;
WHEN SUBOP = 'CALL';
EXSR @CALLS;
WHEN function = 'PROCESS';
objectFound = retrieveObject( exobnm:exobtp );
IF objectFound;
objectFound = ObjectProcess();
ENDIF;
WHEN function = 'RESET';
objectFound = retrieveObject( exobnm:exobtp );
IF objectFound;
objectFound = ResetProcess();
ENDIF;
ENDSL;
z$opt = *BLANK;
IF before <> after;
SELECT;
WHEN p$mode = 'C';
OBJECT = after;
exdesc= '*changed';
WHEN p$mode = 'D';
exdesc = '*deleted';
sflProtect = *ON;
ENDSL;
ENDIF;
z$rrn2 = z$rrn1;
UPDATE SC0320S1;
sflProtect = *OFF;
CLEAR MACRO;
ENDIF;
ENDIF;
ENDDO;
OPM vs ILE
Contrary to popular recruiting terms, there is no such thing as ILE RPG. ILE is not a programming language, it is a modeling concept. The term OPM and ILE are often tied to a version of RPG, but it is a refrence to the model of development. The Original Program Model (OPM) is more limited in scope than the Integrated Language Environment (ILE) model. The Integrated Language Environment has broaden the scope of RPG application developement.| OPM | ILE |
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