RPG (Report Program Generator) is a high-level programming language developed by IBM in 1959 for generating business reports. Over the years, it has grown into a full-fledged general-purpose programming language, especially prominent in the IBM i (formerly AS/400) ecosystem. Although it started as a tool for producing reports from business data, RPG has continuously evolved, keeping pace with modern development practices, particularly with the introduction of RPG IV and its free-format syntax.
In this article, we will explore:
- The origins and history of RPG
- Evolution from RPG II to RPG IV
- The transition from fixed format to free format
- Modern uses of RPG on IBM i
- Why RPG is still relevant today
The Origins of RPG
RPG was originally designed in the late 1950s by IBM as a simpler alternative to assembly language. At the time, businesses were looking for a more efficient way to generate reports from data stored in punch cards and magnetic tapes. IBM introduced RPG as a high-level tool that could describe and generate business reports with minimal programming effort.
Early RPG: Punch Cards and Business Reports
RPG's name comes from its original function: Report Program Generator. Early versions of the language were designed to generate detailed reports from data stored in tabular form. Instead of coding individual instructions, developers could describe the format of a report, and RPG would handle the mechanics of pulling data and formatting it.
The early language was highly structured, and programs were designed to process one record at a time, read from sequential data files. Programmers would use punched cards with fixed columns to define operations, and every line of code adhered strictly to this rigid format.
RPG I and RPG II (1960s - 1970s)
RPG I, the earliest version, quickly became popular for producing business forms, invoices, and financial reports. In 1969, IBM released RPG II, which expanded the language to include more advanced features for data processing, such as indexed file access, conditional logic, and basic arithmetic operations.
Despite its improvements, RPG II remained very rigid in its structure, requiring specific columns for code and making it difficult to read, especially compared to modern languages.
The Evolution of RPG: From RPG III to RPG IV
RPG III (1978)
In the late 1970s, IBM introduced RPG III as part of its System/38 platform, a precursor to the AS/400. RPG III was a major step forward, allowing for more complex data structures, better control over file access, and new ways to organize logic using subroutines.
The structure of RPG III was still fixed-format, meaning that developers had to adhere to column-based code entry, but the language introduced a more modular approach to program design.
The Birth of AS/400 and RPG/400 (1988)
The launch of IBM’s AS/400 in 1988 was a milestone for RPG. The AS/400 became a popular platform for mid-sized businesses and enterprises to manage their IT infrastructure, and RPG/400 became the dominant language used on the platform.
RPG/400 was essentially an enhanced version of RPG III, optimized for the AS/400 environment, but still firmly based on fixed-format coding practices.
The Introduction of RPG IV and Free Format
RPG IV (1994): A New Beginning
The 1990s saw a massive overhaul of RPG with the introduction of RPG IV (also called RPGLE, where LE stands for Integrated Language Environment). RPG IV introduced many modern programming concepts, such as:
- Longer variable names (up to 4096 characters)
- Procedures and modules (allowing for modular, reusable code)
- Support for data types like date, time, and timestamp
- Integration with other languages, including C and SQL
RPG IV was a massive improvement in terms of readability, functionality, and flexibility. It also marked a shift away from column-specific coding toward a more modern and flexible approach.
However, even in RPG IV, the language was still primarily fixed-format, meaning that although the functionality had expanded, developers still needed to follow specific column rules when writing code.
Free Format RPG (2013): Embracing Modern Syntax
In 2013, IBM introduced fully free-format RPG, fundamentally changing how the language looked and felt. With free format, RPG finally shed its historical reliance on fixed columns, aligning with modern coding practices.
Key Features of Free Format RPG:
- No Column Restrictions: Code is no longer constrained by specific columns. Instead, you can write code freely, as with other modern languages like Java, Python, or C.
- Enhanced Readability: The code is easier to read and write. Developers can use indentation, spaces, and line breaks however they see fit, making the code much more maintainable.
- Simplified Syntax: Free format eliminates much of the archaic syntax and introduces clearer, more intuitive instructions.
- Integration with Modern Tools: Free format RPG works seamlessly with modern development tools such as Rational Developer for i (RDi), bringing advanced code editing, debugging, and refactoring tools to the RPG development process.
Here's a quick comparison of fixed-format RPG and free-format RPG:
Fixed Format RPG IV Example:
C 'HELLO' DSPLY C *INLR SETON
Free Format RPG Example:
dcl-s msg char(10) inz('HELLO'); dsply msg; *inlr = *on;
As you can see, the free format version is much more readable and intuitive, removing the old constraints of column-based coding and introducing variable declarations (dcl-s) and inline operations (dsply).
Modern RPG and Its Uses
Today, RPG on IBM i is a powerful language used for building and maintaining mission-critical applications in sectors such as finance, healthcare, logistics, and manufacturing. Many businesses continue to use RPG because of its stability, integration with IBM's robust platforms, and the legacy systems they still depend on.
Typical Use Cases for RPG:
- Enterprise Resource Planning (ERP) Systems: RPG is often used to develop and maintain ERP systems, where it handles massive amounts of transactional data reliably.
- Data Processing Applications: RPG’s original strength in data processing makes it ideal for applications where large datasets need to be processed and reported.
- Web Services and APIs: RPG can be integrated with web services, allowing businesses to expose and consume APIs, making it adaptable to modern web architectures.
- SQL Integration: RPG can natively embed SQL for advanced data manipulation, making it an excellent tool for database-heavy applications.
Why RPG is Still Relevant Today
Despite the explosion of new languages and technologies, RPG remains relevant in the IT world for several reasons:
- Legacy Systems: Many large enterprises still rely on RPG-based applications that were developed decades ago, and replacing or rewriting these systems would be prohibitively expensive.
- Reliability and Performance: RPG programs running on IBM i are known for their exceptional reliability and performance. They handle complex workloads with ease, making them a trusted tool for mission-critical operations.
- Modernization: With free format and integration with modern tools, RPG has modernized itself to remain competitive, giving long-time developers a way to bring legacy systems into the 21st century without completely rewriting codebases.
Conclusion
RPG has come a long way from its origins as a report generator for punch cards. Today, it's a versatile, high-level language capable of handling a wide range of applications, from enterprise resource planning to web services. With the introduction of free format RPG, the language has embraced modern development practices, making it easier to learn, write, and maintain.
In this tutorial series, we will continue exploring RPG free format in detail, starting with its syntax, setup, and how you can leverage it in the IBM i environment.
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