02
Sat, Nov
2 New Articles

RPG Academy: How to Create and Use Procedures

RPG
Typography
  • Smaller Small Medium Big Bigger
  • Default Helvetica Segoe Georgia Times

 

Leverage your OPM RPG knowledge with this simple and practical example of using procedures.

 

I've been getting great feedback from the readers since the first TechTip of this series. I got lots of questions, suggestions, and even some constructive criticism. One of the main "complaints" was that the OPM scenario that was presented in the first TechTip (see Figure 1 below) was too old-fashioned and simplistic.

 

040414RafaelFigure1

Figure 1: This is the traditional OPM scenario.

 

That reader was right, of course. Even in OPM, it's possible to avoid duplicating the same code over and over again in multiple programs. To be fair, a more accurate scenario would be the one depicted in Figure 2, in which the code related with the business rules is isolated in several standalone programs (BR1, BR2…BRx) that are called as needed by programs A and B:

 

040414RafaelFigure2

Figure 2: This is an evolved OPM scenario.

 

This more-realistic and up-to-date scenario will be my starting point for the creation of a simple procedure. I'll stick to the scenario described in the first TechTip: programs A and B both handle inventory, but they do slightly different things. While A imports inventory items from a cargo manifest CSV file, B handles the user inventory management via screen interaction. They both use some of the same business rules, which I've isolated into programs BRx in this new scenario. Let's say that BR1, one of those programs, translates the supplier's item ID into the company's item ID. PGM A would call BR1 whenever it needs to import a new item, passing the external item ID and supplier ID codes and receiving the internal item ID. This means that a PLIst would be defined with the necessary variables:

 

C     PL_BR1       PList                            

C                   Parm                   P_ExtItmID

C                   Parm                   P_SupID  

C                   Parm                   P_IntItmID

 

All of this should be familiar. Now let's transform BR1 into a procedure, step by step.

 

To use a procedure, I need to "tell" the program how to call it, the same way I would do for a program. For that, I'll use a prototype definition. This definition must be used in every program or service program that uses the procedure. Since the idea here is reusing code instead of duplicating it, I usually create a source member in a separate source file, named QCPYLESRC, with all the module's procedure prototypes and include it in the programs/service program where I need to use it. In fact, as you can see below, the prototype definition (shown below as part of the QCPYLESRC/BR_INV_PR source member) is actually quite similar to a PList:

 

* -----------------------------------------------------------------------*

*   Prototype . : BR_INV_PR                                             *

*   Description : Inventory Related Procedures                           *

*   Author .... : Rafael Victoria-Pereira                               *

*   Date ...... : March 2014                                            *

*   Changes ... :                                                       *

* -----------------------------------------------------------------------*

                                                                          

* -----------------------------------------------------------------------*

*   Convert the External Item ID into the Internal Item ID              

* -----------------------------------------------------------------------*

D CvtItmId       PR                                                      

D P_ExtItmID                   50                                        

D P_SupId                     256                                        

D P_IntItmID                   50                                        

                                                                          

Then all I need to do is include this definition in my program/service program, using either /Copy or /Include:

 

* Prototype definition for Inventory Related Procedures

/COPY QCPYLESRC,BR_INV_PR                  

 

Just a note about the procedure name: instead of BR1, I'm using a (slightly) clearer name for the procedure: CvtItmID. I like to use a verb to identity the procedure type (Cvt, short for Convert in this case), followed by the subject (ItmID, short for Item ID). You can argue that ConvertItemID would be even clearer, but it's important to avoid getting carried away with huge names; it will cost you additional time and increase the misspelling chances when you need to call the procedure. Speaking of calling, the way to call a procedure is also different from calling a program:

 

C                   CallP     CvtItmID(P_ExtItmID : P_SupID : P_IntItmID)

 

CallP is used instead of Call, and the parameters follow the procedure name enclosed by parentheses and separated by a colon, just like in a built-in function. You can also use a slightly different notation, similar to a program call with parameters:

 

C                   CallP     CvtItmID(P_ExtItmID :

C                                     P_SupID   :

C                                     P_IntItmID )

 

OK, that's how the procedure is defined and called. Now let's see how to create it! Here's an example of a simple procedure structure, without the actual code:

*-------------------------------------------------------------------------*

*   Convert the External Item ID into the Internal Item ID      

*-------------------------------------------------------------------------*

P CvtItmID       B                   EXPORT                        

D                 PI                                              

D P_ExtItmId                   50                                  

D P_SupId                       10 0                                

D P_IntItmId                   50                                

C*                                                                  

C* The procedure's code goes here                      

C*                                                                

P CvtItmId       E                                                

 

As I explained in the second TechTip of this series, procedures are part of modules. A module can contain one or more procedures. This means that the compiler needs to know where each procedure begins and ends. The P-lines you see above delimit the CvtItmId procedure. Note that the first P-line has the keyword EXPORT. This means that this procedure will be exported by the module; other words, it means that this procedure will be available to the programs and/or service program that are bound to this module.

 

Right after the beginning of the procedure comes the Procedure Interface (PI). The set of D-lines shown here is used to define the procedure's parameters, just like an *Entry PList would in an OPM program. Note that this list begins with a D-line that holds only PI; this marks the start of the Procedure Interface. Also note that the D-lines don't have the usual "S," "C," or "DS" in positions 24-25 for the Definition Type because they are part of the Prototype Interface. It's also possible to define variables within a procedure (more on this in the next TechTip); these variables would be defined using the usual notation in positions 24-25 ("S," "C," or "DS").

 

Finally, there would be a bunch of C-lines containing the actual procedure code, just like in a regular program. One of these lines would assign a value to P_IntItmID, thus allowing the procedure to return the internal item ID to the calling program.

 

Let's do a quick recap. In order to use a procedure in a program or service program, you need to do the following:

  • Define the procedure's prototype (preferably) in a separate source member. I use a member in QCPYLESRC for each module.
  • Create the procedure, respective module, and program or service program, as described in the previous TechTip of this series.

 In your program or service program, do this:

  • Include the source member with the prototype definition in your program/service program using /Copy or /Include.
  • Declare the procedure's parameters. I prefer to use the same names I used in the prototype, but as long as the variable types and lengths match, any name will do.
  • Set up the parameters' values as needed, just like you would do before calling a program with parameters.
  • Call the procedure, using CallP instead of Call.

 

That's all for now! The next TechTip will continue to discuss procedures: when to create them, what you should and shouldn't do, and other interesting things!

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

Now On Sale

BLOG COMMENTS POWERED BY DISQUS

LATEST COMMENTS

Support MC Press Online

$

Book Reviews

Resource Center

  • SB Profound WC 5536 Have you been wondering about Node.js? Our free Node.js Webinar Series takes you from total beginner to creating a fully-functional IBM i Node.js business application. You can find Part 1 here. In Part 2 of our free Node.js Webinar Series, Brian May teaches you the different tooling options available for writing code, debugging, and using Git for version control. Brian will briefly discuss the different tools available, and demonstrate his preferred setup for Node development on IBM i or any platform. Attend this webinar to learn:

  • SB Profound WP 5539More than ever, there is a demand for IT to deliver innovation. Your IBM i has been an essential part of your business operations for years. However, your organization may struggle to maintain the current system and implement new projects. The thousands of customers we've worked with and surveyed state that expectations regarding the digital footprint and vision of the company are not aligned with the current IT environment.

  • SB HelpSystems ROBOT Generic IBM announced the E1080 servers using the latest Power10 processor in September 2021. The most powerful processor from IBM to date, Power10 is designed to handle the demands of doing business in today’s high-tech atmosphere, including running cloud applications, supporting big data, and managing AI workloads. But what does Power10 mean for your data center? In this recorded webinar, IBMers Dan Sundt and Dylan Boday join IBM Power Champion Tom Huntington for a discussion on why Power10 technology is the right strategic investment if you run IBM i, AIX, or Linux. In this action-packed hour, Tom will share trends from the IBM i and AIX user communities while Dan and Dylan dive into the tech specs for key hardware, including:

  • Magic MarkTRY the one package that solves all your document design and printing challenges on all your platforms. Produce bar code labels, electronic forms, ad hoc reports, and RFID tags – without programming! MarkMagic is the only document design and print solution that combines report writing, WYSIWYG label and forms design, and conditional printing in one integrated product. Make sure your data survives when catastrophe hits. Request your trial now!  Request Now.

  • SB HelpSystems ROBOT GenericForms of ransomware has been around for over 30 years, and with more and more organizations suffering attacks each year, it continues to endure. What has made ransomware such a durable threat and what is the best way to combat it? In order to prevent ransomware, organizations must first understand how it works.

  • SB HelpSystems ROBOT GenericIT security is a top priority for businesses around the world, but most IBM i pros don’t know where to begin—and most cybersecurity experts don’t know IBM i. In this session, Robin Tatam explores the business impact of lax IBM i security, the top vulnerabilities putting IBM i at risk, and the steps you can take to protect your organization. If you’re looking to avoid unexpected downtime or corrupted data, you don’t want to miss this session.

  • SB HelpSystems ROBOT GenericCan you trust all of your users all of the time? A typical end user receives 16 malicious emails each month, but only 17 percent of these phishing campaigns are reported to IT. Once an attack is underway, most organizations won’t discover the breach until six months later. A staggering amount of damage can occur in that time. Despite these risks, 93 percent of organizations are leaving their IBM i systems vulnerable to cybercrime. In this on-demand webinar, IBM i security experts Robin Tatam and Sandi Moore will reveal:

  • FORTRA Disaster protection is vital to every business. Yet, it often consists of patched together procedures that are prone to error. From automatic backups to data encryption to media management, Robot automates the routine (yet often complex) tasks of iSeries backup and recovery, saving you time and money and making the process safer and more reliable. Automate your backups with the Robot Backup and Recovery Solution. Key features include:

  • FORTRAManaging messages on your IBM i can be more than a full-time job if you have to do it manually. Messages need a response and resources must be monitored—often over multiple systems and across platforms. How can you be sure you won’t miss important system events? Automate your message center with the Robot Message Management Solution. Key features include:

  • FORTRAThe thought of printing, distributing, and storing iSeries reports manually may reduce you to tears. Paper and labor costs associated with report generation can spiral out of control. Mountains of paper threaten to swamp your files. Robot automates report bursting, distribution, bundling, and archiving, and offers secure, selective online report viewing. Manage your reports with the Robot Report Management Solution. Key features include:

  • FORTRAFor over 30 years, Robot has been a leader in systems management for IBM i. With batch job creation and scheduling at its core, the Robot Job Scheduling Solution reduces the opportunity for human error and helps you maintain service levels, automating even the biggest, most complex runbooks. Manage your job schedule with the Robot Job Scheduling Solution. Key features include:

  • LANSA Business users want new applications now. Market and regulatory pressures require faster application updates and delivery into production. Your IBM i developers may be approaching retirement, and you see no sure way to fill their positions with experienced developers. In addition, you may be caught between maintaining your existing applications and the uncertainty of moving to something new.

  • LANSAWhen it comes to creating your business applications, there are hundreds of coding platforms and programming languages to choose from. These options range from very complex traditional programming languages to Low-Code platforms where sometimes no traditional coding experience is needed. Download our whitepaper, The Power of Writing Code in a Low-Code Solution, and:

  • LANSASupply Chain is becoming increasingly complex and unpredictable. From raw materials for manufacturing to food supply chains, the journey from source to production to delivery to consumers is marred with inefficiencies, manual processes, shortages, recalls, counterfeits, and scandals. In this webinar, we discuss how:

  • The MC Resource Centers bring you the widest selection of white papers, trial software, and on-demand webcasts for you to choose from. >> Review the list of White Papers, Trial Software or On-Demand Webcast at the MC Press Resource Center. >> Add the items to yru Cart and complet he checkout process and submit

  • Profound Logic Have you been wondering about Node.js? Our free Node.js Webinar Series takes you from total beginner to creating a fully-functional IBM i Node.js business application.

  • SB Profound WC 5536Join us for this hour-long webcast that will explore:

  • Fortra IT managers hoping to find new IBM i talent are discovering that the pool of experienced RPG programmers and operators or administrators with intimate knowledge of the operating system and the applications that run on it is small. This begs the question: How will you manage the platform that supports such a big part of your business? This guide offers strategies and software suggestions to help you plan IT staffing and resources and smooth the transition after your AS/400 talent retires. Read on to learn: