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RPG Academy: /FREE Your Code - It's /FREE, But It Has Rules

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If you read the previous article of this series and concluded that the pros outweigh the cons, it's now time to learn the rules of coding in free-format. Don't worry, they're few, and most are common sense!

For the compiler to correctly validate and compile your code, there are a few rules that you have to follow, just like the fixed positions that you already know. These rules will become so natural over time that you won't even think about them. Let's review the rules one by one, and then look at a simple code sample:

  • Obviously, you can write code wherever you want in free-format, between columns 8 and 80. Just make sure to leave columns 6 and 7 blank.
  • In order for the compile to recognize free-format code, each block of it must be enclosed in the /FREE and /END-FREE directives. However, note that if you're running V7, there's a PTF that, among other things, removes this restriction. (I'll talk about it in a later article.) And yes, you can mix fixed- and free-format code in the same source, even in the same routine or procedure.
  • Your statements can span multiple lines, but only one statement, no matter how short, is allowed per line. This is especially helpful when calling functions with long parameter lists or with nesting functions.
  • To help the compiler figure out where your instruction ends, you must end it with the semicolon (;) character. (Note that I'm referring to an "instruction" instead of a line of code because it can now span multiple lines.) It's really a pain at first, but it will (hopefully) become so natural that you'll do it without thinking.
  • Each instruction now starts with its respective operation code, even those that require Factor 1 to be specified. The rest of the structure remains the same, without the positional constraints. The "new" structure is <Operation Code> <Factor 1> <Factor 2> <Result>.
  • You can have code instructions and comments in the same line. Just be sure to end the instruction with a semicolon and prefix the comment with double slashes (//). You'll see examples in the next TechTip that will make this clearer.
  • Some operation codes are not supported in free-format. (I mentioned this earlier, but it's important because it will be a pain, even bigger than getting used to ending code statements with semicolons.) Don't worry; I'll go over the full list of these operation codes later in this series, providing free-format-compatible alternatives.
  • Since there aren't fixed columns (between positions 8 and 80, at least), those old friends the positional indicators (used in some operation codes with varied functions) are not supported. If you've read some of the previous TechTips of this series, namely the one about getting rid of file-related indicators, though, this shouldn't be a problem for you. Again, I'll illustrate this with a few examples of operation codes in fixed- and free-format.

Don't be alarmed by the number of rules. It might seem a lot right now, but with some examples and a bit of practice, they will seem logical. Let's try to consolidate the rules with a simple example, in fixed- and free-format.

A First Taste of Free-Format Code

If you skipped directly to this section, please read the rules from the previous section. It'll make the task of fully understanding what's going on much easier.

Here's a typical RPG operation: reading a file and writing its contents to a printer file. I'll skip the H- and F-lines because, for the moment, I'll keep using the fixed-format specs that you're used to. I'll cover those very exciting changes that make RPG (almost) completely free-format later in the series. I know I keep saying this, but it's impossible to discuss everything at once!

This is familiar fixed-format code:

C                 EXCEPT   HDR_REC

C                 READ     MYFILE

C                 DOW       NOT %EOF(MYFILE)

C                 EXCEPT   DET_REC

C                 READ     MYFILE

C                 ENDDO                                  

Here, it becomes free-format code:

/FREE

   EXCEPT HDR_REC;

   READ MYFILE;

   DOW NOT %EOF(MYFILE);

      EXCEPT DET_REC;

      READ MYFILE;

   ENDDO;

/END-FREE

The most notable differences, other than the obvious column-free style, are the /FREE and /END-FREE directives and the semicolon at the end of each line of code. There's another subtle difference that's not mandatory (for the compiler at least) but that dramatically increases readability: indentation. Notice how I indented the two lines of code inside the DOW block; simply adding two blank spaces before those lines makes it immediately obvious that they belong to the DOW block.

This is just a simple example to get you a first taste of free-format. The next TechTip will provide more of them and discuss a few more subtleties of free-format that you need to be aware of. Until then, share your thoughts and doubts in the comments section below.

Rafael Victoria-Pereira

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.

Evolve Your RPG Coding: Move from OPM to ILE...and Beyond Evolve Your RPG Coding: Move from OPM to ILE...and Beyond
Transition to modern RPG programming with this step-by-step guide through ILE and free-format RPG, SQL, and modernization techniques.
List Price $79.95

Now On Sale

Flexible Input, Dazzling Output with IBM i Flexible Input, Dazzling Output with IBM i
Uncover easier, more flexible ways to get data into your system, plus some methods for exporting and presenting the vital business data it contains.
List Price $79.95

Now On Sale
SQL for IBM i: A Database Modernization Guide SQL for IBM i: A Database Modernization Guide
Learn how to use SQL’s capabilities to modernize and enhance your IBM i database.
List Price $79.95

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