It's time for a few more examples of free-format code, which help you memorize the coding rules and will speed up your transition to this new coding style.
The previous TechTip introduced the rules you need to abide by to write code in free-format and provided a simple example. This time around, I'll provide additional examples and discuss a few important things you'll need to keep in mind while coding in this new way.
Let's pick up where we stopped in the previous TechTip and look at another example of how indenting improves readability. The next code samples include instructions with code blocks inside other code blocks and also show how Factor 1, not used in the example from last time, is used in free format:
C K_MYKEY SETLL MYFILE
C IF %EQUAL
C K_MYKEY READE MYFILE
C DOW NOT %EOF(MYFILE)
C EXCEPT DET_REC
C READ MYFILE
C ENDDO
C ELSE
C EXCEPT NoDet_REC
C ENDIF
Once again, this should be easy as pie in free format:
/FREE
SETLL K_MYKEY MYFILE;
IF %EQUAL;
READE K_MYKEY MYFILE;
DOW NOT %EOF(MYFILE);
EXCEPT DET_REC;
READ MYFILE;
ENDDO;
ELSE;
EXCEPT NoDet_REC;
ENDIF;
/END-FREE
The indentation makes the different code blocks more noticeable than ever, right?
In a fixed-format piece of code, having a sequence of nested IF statements makes it hard to understand where each of them ends:
C IF P_Age >= 20 and P_Sex = 'F'
C EVAL W_Code = 5
C ELSE
C IF P_Age >= 20 and P_Sex = 'M'
C EVAL W_Code = 4
C ELSE
C IF P_Age >= 30 and P_Sex = 'F'
C EVAL W_Code = 10
C ELSE
C IF P_Age >= 30 and P_Sex = 'M'
C EVAL W_Code = 9
C ELSE
C EVAL W_Code = 20
C ENDIF
C ENDIF
C ENDIF
C ENDIF
You can replace those ELSE/IF blocks of lines by a single ELSEIF to make it more readable:
C IF P_Age >= 20 and P_Sex = 'F'
C EVAL W_Code = 5
C ELSEIF P_Age >= 20 and P_Sex = 'M'
C EVAL W_Code = 4
C ELSEIF P_Age >= 30 and P_Sex = 'F'
C EVAL W_Code = 10
C ELSEIF P_Age >= 30 and P_Sex = 'M'
C EVAL W_Code = 9
C ELSE
C EVAL W_Code = 20
C ENDIF
It's certainly an improvement over all those sets of ELSE followed by IF, but if there is more than one instruction after the ELSEIF, it can still get a bit confusing. That doesn't happen in free-format, assuming that the proper indentation is used:
/FREE
IF P_Age >= 20 and P_Sex = 'F';
W_Code = 5;
ELSEIF P_Age >= 20 and P_Sex = 'M';
W_Code = 4;
ELSEIF P_Age >= 30 and P_Sex = 'F';
W_Code = 10;
ELSEIF P_Age >= 30 and P_Sex = 'M';
W_Code = 9;
ELSE;
W_Code = 20;
ENDIF;
/END-FREE
Personally, I think a SELECT block is clearer than an IF/ELSEIF block. As long as you use proper indentation, either of the two solutions works, but I still prefer this:
/FREE
SELECT;
WHEN P_Age >= 20 and P_Sex = 'F';
W_Code = 5;
WHEN P_Age >= 20 and P_Sex = 'M';
W_Code = 4;
WHEN P_Age >= 30 and P_Sex = 'F';
W_Code = 10;
WHEN P_Age >= 30 and P_Sex = 'M';
W_Code = 9;
OTHER;
W_Code = 20;
ENDSL;
/END-FREE
Don't worry about the missing EVAL operation codes; I'll get to that in a minute. Now, let's go back to the READE example from earlier to explain something I missed:
READE K_MYKEY MYFILE;
Notice how the READE line is written:
<Operation Code> <Factor 1> <Factor 2>
That's different from the usual format:
<Factor 1> <Operation Code> <Factor2>
This is just one of the things you need to get used to.
There are other things that might confuse you, such as the fact that EVAL and CALLP are optional, except when you need to use their extenders. You probably noticed this in the IF/ELSEIF example I just presented. The missing EVALs will seem a bit alien at first, but you'll eventually get used to it!
Not everything is "strange." Let me show you something that you'll certainly like. Here's a typical fixed-format piece of code:
C K_MYKEY CHAIN MYFILE
C IF %FOUND(MYFILE)
C EXSR CustFound
C ELSE
C EXSR NoCust
C ENDIF
Now, let's take advantage of the possibility of having longer names to make this clearer in free-format:
/FREE
CHAIN KEY MYFILE;
IF %FOUND(MYFILE);
EXSR Customer_Found;
ELSE;
EXSR Customer_Not_Found;
ENDIF;
/END-FREE
You have to admit that Customer_Not_Found is clearer than NoCust. This can be made even clearer with a few comments:
/FREE
CHAIN KEY MYFILE;
IF %FOUND(MYFILE);
EXSR Customer_Found; // Retrieve customer info
ELSE;
EXSR Customer_Not_Found; // Fill fields with N/A
ENDIF;
/END-FREE
Unlike in fixed-format, where comments need a line for themselves, in free-format you can mix code and comment in the same line, which allows for more precise and unobtrusive documentation. This is also an interesting approach to "modern" languages, where this in-line commenting is common.
Speaking of modern languages, here's something else that might be a bit confusing: you remember this line from the EVAL example, right? This code…
C EVAL W_Some_Number = W_Some_Number + 1
…became this:
W_Some_Number = W_Some_Number + 1;
Well, there's another, shorter notation in free-format that RPG got from "modern" languages:
W_Some_Number += 1;
You'll find this particular form (+= 1) frequently in counter variables. This is called compound assignment, and you can use it with the following operators:
- target += expression: The expression is added to the target.
- target -= expression: The expression is subtracted from the target.
- target *= expression: The target is multiplied by the expression.
- target /= expression: The target is divided by the expression.
- target **= expression: The target is assigned the target raised to the power of the expression.
For instance, the following cuts W_Some_Number in half:
W_Some_Number /= 2
I hope that you're now convinced, ready, and willing to start converting your code to free-format. It's an easy process, but there are some pitfalls. The next TechTips will provide valuable information on how you can start converting your code and finally leave one of the biggest anachronisms of RPG behind!
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