If you’re staring at a wall of crusty RPG III or RPG/400 code and thinking, “Let’s just convert this to free-format RPGLE,” hold up. Modernization isn’t just about changing the syntax, it’s about rethinking the logic, streamlining the structure, and embracing modern opcodes that make your code cleaner, faster, and easier to maintain.
The Old Way: RPG/400 Fixed Format
Here’s a classic loop from the 1980s:
C DO 100 I
C Z-ADD I VALUE 10 0
C ADD VALUE TOTAL
C ENDDO
C SETON LR
This works. But it’s verbose, clunky, and full of unnecessary steps.
Why Z-ADD when you can just declare and assign? Much as I love the Z-ADD opcode, the modern EVAL just makes more sense.
The Refactored Way: RPGLE Free Format with Modern Opcodes
ctl-opt dftactgrp(*no) actgrp(*caller);
dcl-s total int(10);
for i = 1 to 100;
total += i;
endfor;
*inlr = *on;
Boom. No Z-ADD. No temporary variables. Just clean, readable logic using for, +=, and dcl-s.
Don’t Just Convert, Think and Improve (Refactor)!
Here’s another example. Old-style conditional logic:
C IF FIELD1 = 'X'
C EXSR SUBRX
C ENDIF
C EXSR SUBRY
C ENDIF
C EXSR SUBRZ
C ENDIF
Refactored might look something like this:
read FILE1;
fieldValue = FIELD1;
select;
when fieldValue = 'X';
exsr SubroutineX;
exsr SubroutineY;
exsr SubroutineZ;
endselect;
Better yet, replace EXSR with a proper subprocedure in a service program. That’s real modernization.
Modern Opcodes You Should Be Using
for, dow, dou → Replace DO loops
select, when, other → Replace nested IF/ELSE
dcl-s, dcl-pi, dcl-pr → Replace I and C specs
%trim, %subst, %scan, %check → Replace manual string manipulation
%error, %found, %eof → Replace status indicators
Clean Code Is Maintainable Code
Modern RPG isn’t just about free-format, it’s about clarity, modularity, and efficiency. Refactoring lets you:
- Remove legacy cruft
- Use built-in functions
- Break logic into reusable procedures
- Write code that future-you (or your junior devs) will actually understand
Final Thoughts
Modernizing RPG code is like renovating a house. You don’t just slap on a new coat of paint you check the wiring, knock down walls, and maybe add a hot tub. So don’t just convert your RPG/400 code to free-format RPGLE. Refactor it. Rethink it. Rebuild it.