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Is RPG IV Consistent for You?

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Recently, I made a casual comment in an MC Press Forums thread about some features in RPG being implemented inconsistently. I thought I would share my specific points with everyone and put them to rest once and for all.

First, I think the new features in RPG IV are great. The fact that we can parse XML, write subprocedures, and use qualified data structures is fantastic! The programmers at IBM Toronto are doing a great job of creating new features for the RPG IV language. The issue I want to address is specifically about delivery, not about the quality or quantity of the product's features ("the product" being the RPG IV language).

Several times per year, I head off to some iSeries shop in North America to teach RPG IV. Mostly, I'm asked to train people in areas of RPG IV that were not available with RPG III, such as subprocedures, expressions, and service programs. Usually, by the time I arrive, the requirement has been amended to include an update on the latest and greatest features of RPG IV. This is when I get nervous. I have to ask the client, "What release(s) of OS/400 are you running?"

Most shops I teach in have multiple iSeries boxes. The vast majority are not running the same release level on both boxes—but some are. Rarely will I see a shop with V4R5 and V5R3. Most shops that run multiple boxes are usually just one or two releases apart. Today, I usually see a V5R1 box for production with a V5R2 or V5R3 box for development. But lately, more and more V5R2/V5R3 combinations are showing up. Some shops have V5R3 or V5R4 installed on the primary box and V5R1 installed on the secondary system.

This can create a high level of apprehension for me. Why? Because RPG IV at V5R2 is significantly different than it is at V5R1. This difference widens between V5R1 and V5R3 and V5R4.

The mere fact that RPG IV at V5R3 has features that do not exist in V5R1 causes me to have to fragment the lecture and say, "If you're on V5R2, do it this way; if you're on V5R3; do it that way; and if you're on V5R1, you can't do it." Not only am I embarrassed by this, the programmers I'm teaching (and their management) are lightheartedly frustrated.

Take qualified data structures for example. Certainly, this feature is arguably the single best, most important improvement to RPG IV since subprocedures were added. Qualified data structures were added in V5R1. In V5R2, an enhancement to qualified data structures was announced: the so-called "nested data structures," which are the completion of the qualified data structures feature. Certainly, nested data structures do not require anything from OS/400 that was introduced in V5R2. So why don't programs compiled with nested data structures run on V5R1 systems?

Since they don't, I have to teach this fragmented feature to my clients: "If you're on V5R2, you can use qualified data structures and nested data structures. But if you're on V5R1, you can only use qualified data structures."

RPG IV is not a standard end-user application that needs to have enhancements added to it in every freaking release. I'd rather wait for a new version or "base release" of OS/400 and have RPG IV's features target that release level and later than have a handful of features added like breadcrumbs on each point release.

This doesn't mean the RPG IV compiler developers in Toronto are doing something wrong. They should be creating new features and fixing existing ones. But it could mean that the RPG IV compiler is being packaged or distributed in a confusing way.

Sure, there are a lot of Lone Ranger RPG coders out there who want the latest and greatest features as soon as they come out. They install V5R3 or V5R4 or V5R5 so they can use the new RPG IV opcodes. OK, those 20 people can stand down; your presence has been duly noted. Heck, I was one of those people (in fact, I think I started that trend).

I don't know why, but perhaps I see things differently today than I used to.

I don't understand why a programming language needs new opcodes on every release of the operating system. It's not like Windows, where a new version comes out every three or four years and the OS vendor ships an updated set of compilers. They do that so that the compilers support the new features in the OS that were not available in the prior version of the OS.

Traditionally, a runtime library is eventually introduced (as will be done for Windows XP when Windows Vista ships) that allows programs written specifically to the Vista API to run on XP.

And yet with iSeries, we can't seem to figure out how to get a subtle change in the syntax of the RPG IV PREFIX keyword to compile to TGTRLS(*PRV).

Speaking of subtle syntax issues, look at the syntax changes for the PREFIX, DTAARA, EXTPROC, and other keywords over the release. Look at the myriad keywords for the Header spec—I can't even remember most of them. One of my favorites is OPENOPT(*INZOFL). Can anybody tell me what this does off the top of their head? A search of the Web might give you the answer, but does that justify it?

Also take a look at the %char, %dec, %date, and other related built-in functions. A subtle change throughout each V5 release allows them to be used to convert directly between character, numeric, and date data types. If you are running V5R3, you get the full and complete feature set, but if you're running earlier V5 releases, you get only partial support. If you're running V4, you don't get anything.

Certainly, RPG IV needs new features. But the fact that we get them delivered on V5R3 and they don't work on V5R2 means they are unusable until V5R3. By the time we've moved to V5R3, we've forgotten about these new features, yet people are already talking about the V5R4 features that we can't use on our V5R3 system.

What's the solution? Well, it isn't going to happen. We will continue to see new features in RPG IV that do not work on previous release levels until the day IBM stops enhancing RPG IV. And we certainly don't want that day to come! So, for now, we need to take the bad with the good.

Bob Cozzi is a programmer/consultant, writer/author, and software developer of the RPG xTools, a popular add-on subprocedure library for RPG IV. His book The Modern RPG Language has been the most widely used RPG programming book for nearly two decades. He, along with others, speaks at and runs the highly-popular RPG World conference for RPG programmers.


Bob Cozzi is a programmer/consultant, writer/author, and software developer. His popular RPG xTools add-on subprocedure library for RPG IV is fast becoming a standard with RPG developers. His book The Modern RPG Language has been the most widely used RPG programming book for more than a decade. He, along with others, speaks at and produces the highly popular RPG World conference for RPG programmers.

MC Press books written by Robert Cozzi available now on the MC Press Bookstore.

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