Most fixed-format op codes are available in free-format, but IBM left a few behind (rightfully so, if you ask me). This article will help you replace COMP, CASXX, CABXX, TAG, and GOTO when converting to free-format.
The operation codes discussed in the previous article were the easier ones. Let’s move on to more-complicated operation codes, which will certainly require some time to properly convert to free-format.
When it comes to comparing stuff, RPG’s options go well beyond other languages; most languages don’t have anything like COMP or CASXX. In an effort to bring RPG a step closer to the norm, IBM decided to drop these operation codes. They don’t have a BIF alternative, but you can emulate their functionality using logical expressions. Let’s start with COMP:
C W_AFld COMP W_OtherFld 101112
In case you don’t remember how to use it, here goes:
- If the second field is greater than the first, then *IN11 (the one in the middle of the indicator group in this example) is set to *ON, while the other two are set to *OFF.
- If the situation is reversed, then *IN10 (the one on the left side) is set to *ON, while the other two are set to *OFF.
- Finally, if both variables contain the same value, *IN12 (the one on the right side) is set to *ON, and the other two are set to *OFF.
If you read these rules carefully, it gets easy to translate them into free-format, and to get rid of the indicators at the same time!
Suppose you want to do something when the second field is greater than the first. Writing this in free-format is simple:
/FREE
IF W_OtherFld > W_AFld;
// do something here…
ENDIF;
/END-FREE
Before moving on to CASXX operations and because I mentioned indicators, let me just say that SETON and SETOFF were also excluded from free-format. However, much like the arithmetic operation codes I mentioned in the previous TechTip, you can have the same functionality with EVAL:
C SETON 10
This can be replaced by the following:
*IN10 = *On;
I hope that after what you’ve read so far, you don’t feel the need to use indicators in the code that you write or convert to free-format. As I said before, there are only a handful of situations in which you can’t escape indicators—mainly related to display and printer files—so please, when modernizing your code, ban the indicators, or at least use named indicators. If you’re not familiar with the named indicators technique, don’t worry because I’ll explain it in a future article.
Replacing CASXX operation codes is also fairly simple. If you think about the functionality they provide—compare two things and execute a subroutine if the condition implied in the instruction is met—you’ll see that this can be replaced by an IF block with a EXSR inside. Let’s look at an example:
C W_CurLine CASGE W_MaxLines PAG_BRK
This is replaced by the following:
/FREE
IF W_CurLine >= W_MaxLines;
EXSR PAG_BRK;
ENDIF;
/END-FREE
That’s a straightforward and elegant solution when compared with the cryptic, fixed-format equivalent.
Goodbye Spaghetti Code: No More CABXX, TAG, and GOTO
The next three operation codes don’t have a replacement—direct or indirect—in free-format. And if you ask me, that’s a good thing.
First, I’m talking about the CABXX operation code. “Compare and Branch” has been around for ages; it’s one of the workhorses of “old” RPG. If you’re not familiar with it, the functionality provided by CABXX is similar to CASXX. The difference is that it doesn’t execute a subroutine; it “jumps” to a label somewhere else in the code. The thing is—and this is why I mentioned three operation codes that don’t have a free-format replacement—TAG (the way to indicate a label) and GOTO (another way to jump to a label) were dropped for the sake of readability (and getting rid of the dreaded spaghetti code, hallmark of older versions of RPG). So, you’ll need to reengineer your code to “convert” the CABXX, TAG and GOTO operations to free format. Let’s explore the options.
Sometimes, a TAG and a GOTO delimit a piece of code that could be a subroutine or even a procedure in better-structured source code; using the CASXX free-format alternative might be a solution for these cases. However, there are times when you just need to “jump” to a particular place in the code—leave a cycle or a subroutine, for instance. For these cases, there is ITER (iterate), which jumps to the top of a loop. It can be any type of loop: DOWXX, DOUXX, or FOR. There’s also LEAVE, which jumps out of the loop, and LEAVESR, which (you guessed it) leaves the subroutine.
For the rest of the GOTO situations, you need to take a good hard look at the code and decide what to do. It’s not the best of solutions, but you can decide to leave it as-is (for a while, at least), because you can mix fixed- and free-format code, as long as you signal the beginning and end of your free-format code with the appropriate directives. I’m not encouraging you to leave those GOTOs permanently—just until you get some experience with the whole ILE thing.
What’s your take on this? I know that this is a controversial topic, probably as much as the file-related indicators, so feel free to speak you mind in the comments sections below!
The next TechTip will close the fixed-to-free format conversion topic, with a discussion about array-related operation codes in free-format.
Rafael Victória-Pereira has more than 20 years of IBM i experience as a programmer, analyst, and manager. Over that period, he has been an active voice in the IBM i community, encouraging and helping programmers transition to ILE and free-format RPG. Rafael has written more than 100 technical articles about topics ranging from interfaces (the topic for his first book, Flexible Input, Dazzling Output with IBM i) to modern RPG and SQL in his popular RPG Academy and SQL 101 series on mcpressonline.com and in his books Evolve Your RPG Coding and SQL for IBM i: A Database Modernization Guide. Rafael writes in an easy-to-read, practical style that is highly popular with his audience of IBM technology professionals.
Rafael is the Deputy IT Director - Infrastructures and Services at the Luis Simões Group in Portugal. His areas of expertise include programming in the IBM i native languages (RPG, CL, and DB2 SQL) and in "modern" programming languages, such as Java, C#, and Python, as well as project management and consultancy.
MC Press books written by Rafael Victória-Pereira available now on the MC Press Bookstore.
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