IBM RPG

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RPG
Report Program Generator
Paradigm(s) Multi-paradigm
Developer IBM
Appeared in 1959
Stable release RPG IV version 7 release 1 / April 23, 2010 (2010-04-23)
Typing discipline Strong, static
Dialects RPG, RPG II, RPG III, RPG 400, RPG IV, RPG/ILE; RPG/Free, Baby/36, Baby/400, Lattice RPG
Influenced by 9PAC, FARGO
Influenced RPG II
OS CPF, SSP, OS/400, OS/VS1, z/OS, VS/9, PRIMOS, OpenVMS, Burroughs MCP, Windows

RPG is a high-level programming language (HLL) for business applications. RPG is an IBM proprietary language and is today available only on IBM i or OS/400 based systems.[1]

It has a long history, having been developed by IBM in 1959 as the Report Program Generator - a tool to replicate punched card processing on the IBM 1401[2] then updated to RPG II for the IBM System/3 in the late 1960s, and since evolved into an HLL equivalent to COBOL and PL/I.

It remains a popular programming language on the IBM Power i platform as well as on the current IBM i where the current version, RPG IV (a.k.a. ILE RPG), provides a modern programming environment.

Overview[edit]

An RPG program once typically started off with File Specifications, listing all files being written to, read from or updated, followed by Data Definition Specifications containing program elements such as Data Structures and dimensional arrays, much like a "Working-Storage" section of a COBOL program or "var" statements in Pascal. This is followed by Calculation Specifications, which contain the executable instructions. Output Specifications can follow which can be used to determine the layout of other files or reports. Alternatively files, some data structures and reports can be defined externally, mostly eliminating the need to hand code input and output ("I/O") specifications.

In the early days of RPG, its major strength was known as the program cycle: every RPG program executes within an implied loop, which can apply the program to every record of a file. At that time each record (individual punched card) would be compared to each line in the program, which would act upon the record, or not, based upon whether that line had an "indicator" turned "on" or "off" — from a set of logical variables numbered 01–99 for user-defined purposes, or other smaller sets based upon record, field, or report processing functions. The concept of level breaks and matching records is unique to the RPG II language, and was originally developed with card readers in mind.

Since the introduction of the System 38 in 1979 most RPG programmers discontinued use of the cycle in favor of controlling program flow with standard looping constructs, although IBM has continued to provide backward compatibility for the cycle.

History[edit]

RPG is one of the few languages created for punched card machines that is still in common use today. This is because the language has evolved considerably over time. It was originally developed by IBM in 1959. The name Report Program Generator was descriptive of the purpose of the language: generation of reports from data files, including matching record and sub-total reports.

FARGO (Fourteen-o-one Automatic Report Generation Operation) was the predecessor to RPG on the IBM 1401 . Both languages were intended to facilitate ease of transition for IBM tabulating machine (Tab) unit record equipment technicians to the then new computers.

Tab machine technicians were accustomed to plugging wires into control panels to implement input, output, control and counter operations (add, subtract, multiply, divide). Tab machines programs were executed by impulses emitted in a machine cycle; hence, FARGO and RPG emulated the notion of the machine cycle with the program cycle. RPG was superior to and rapidly replaced FARGO as the report generator program of choice.

The alternative languages generally available at the time were Assembler, COBOL or FORTRAN. COBOL was a natural language-like business oriented language and FORTRAN was a language that facilitated mathematical applications. Other languages of the era included ALGOL and Autocoder and a few years later PL/I. Assembler and COBOL were more common in mainframe business operations (System/360 models 30 and above) and RPG more commonly used by customers who were in transition from tabulating equipment (System/360 model 20).

Language evolution[edit]

RPG II was introduced with the System/3 series of computers. It was later used on System/32, System/34, and System/36, with an improved version of the language. ICL also produced a version on its VME/K operating system

RPG III was created for the System/38 and its successor the AS/400. RPG III significantly departed from the original language, providing modern structured constructs like IF-ENDIF blocks, DO loops, and subroutines (RPG2 Supported Subroutines). RPG III was also available for larger systems including the IBM System/370 mainframe running OS/VS1. It was also available from Unisys for the VS/9 operating system running on the UNIVAC Series 90 mainframes.

DE/RPG or Data Entry RPG was exclusively available on the IBM 5280 series of data-entry workstations in the early '80s. It was similar to RPG III but lacking external Data Descriptions (DDS) to describe data(files) like on the System/38 and its successors. Instead, the DDS part had to be included into the RPG source itself.

RPG/400 was effectively RPG III running on AS/400. IBM renamed the RPG compiler as "RPG/400" but at the time of its introduction it was identical to the RPG III compiler on System/38. The rebranding took place to differentiate between the earlier CISC (Complex Instruction Set Compiler) on the beige boxes to the later, "faster" RISC (Reduced Instruction Set Compiler), usually on the black servers. Virtually all IBM products were rebranded as xxx/400 and the RPG compiler was no exception. RPG III compiled with the RPG/400 compiler offered nothing new to the RPG III language until IBM began development of new operation codes, such SCAN, CAT and XLATE after several years of AS/400 availability. These enhancements to RPG III were not available in the System/38 version of RPG III.

RPG IV (a.k.a. RPGLE and ILE RPG[3]) was released in 1994 and the name, officially, was no longer an initialism. RPG IV offered a greater variety of expressions within its Extended Factor-2 Calculation Specification and, later in life, its free-format Calculation Specifications and Procedure syntax. RPG IV is the only version of RPG supported by IBM in its long line of successors to the AS/400 system (iSeries, etc.).

RPG IV[edit]

In 2001, with the release of OS/400 V5R1, RPG IV offered greater freedom for calculations than offered by the Extended Factor-2 Calculation Specification: a free-format text-capable source entry, as an alternative to the original column-dependent source format. The "/FREE" calculation did not require the operation code to be placed in a particular column; the operation code is optional for the EVAL and CALLP operations; and syntax generally more closely resembles that of mainstream, general-purpose programming languages. Until October 2013, the free format only applied to the calculation specifications.[4] With the V7R1 TR7 upgrade to the language, the "/free" and "/end-free" calculations are no longer necessary, and the language has finally broken the ties to punched cards.

Today, RPG IV is a more robust language. Editing can still be done via the simple green screen editor (even though syntax checking is not supported for features introduced from OS 7.1 onwards) or it can be edited via PC using IBM's Websphere Development Studio, now named RDi (Rational Development Studio for i) a customized implementation of Eclipse. IBM is continually extending its capabilities and adding more built-in functions (BIFs). It has the ability to link to Java objects,[5] and i5/OS APIs; it can be used to write CGI programs with the help of IBM's Cgidev2 web toolkit,[6] RPGLIB (a collection of hundreds of pre-written RPG IV routines), CGILIB, the RPG Toolbox, and other commercial Web-enabled packages. Even with the changes, it retains a great deal of backward compatibility, so an RPG program written 37 years ago could run today with little or no modification.

The SQL Precompiler allows current RPG developers to take advantage of IBM's cost-based SQE (SQL Query Engine). With the traditional F-Spec approach a developer had to identify a specific access path to a data set, now they can implement standard embedded SQL statements directly in the program. When compiled, the SQL Precompiler transforms the invalid embedded SQL statements into valid RPG statements that call the database manager programs that ultimately implement the query request.

In 2006 OS/400 was renamed i5/OS to correspond with the new IBM System i5 branding initiative; the 5 was later dropped in favor of just System i. In March 2008 i5/OS was renamed IBM i as part of the Power Systems consolidation of System i and System p product lines. The new Power Systems also adopt more mainstream version numbers, substituting 6.1 for the twenty-year-old V1R1M0 notation. The latest release is now referred to as IBM i 7.1 and fully supports the RPG IV language, as well as many others. WebSphere Development Studio Client (WDSC) is now referred to as Rational Developer for i (RDi), of which three product levels are available. They are called Rational Developer for i (RDi), RDi Service Oriented Architecture (RDi SOA), and Rational Application Developer (RAD). The new lineup provides in more granular packaging all of the development tools and support previously offered by WDSC and WDSC Advanced Edition.

The language is based on the EBCDIC character set, but also supports UTF-8, UTF-16 and many other character sets. The threadsafe aspects of the language are considered idiosyncratic by some as the compiler team has addressed threads by giving each thread its own static storage, rather than make the RPG run-time environment re-entrant. This has been noted to muddle the distinction between a thread and a process (making RPG IV threads a kind of hybrid between threads and processes).

RPG Open Access[edit]

Launched in 2010 with the full name of Rational Open Access: RPG Edition.

Upon its launch, IBM i Chief Architect Steve Will described it as an 'enhancement that’s really an architectural change that opens RPG up to whole new uses. And it’s being brought to the community by IBM i, our friends in IBM Rational, and several ISVs who’ve been working with IBM to hit the ground running. The idea behind the new capability is to remove the necessity for all output from RPG programs to be forced into the limited 5250 data stream. Instead, it can be passed to handlers, which can transform it in any way the handler wants. Wrap it in XML; put it in the format required by a pervasive device; make a Web page that doesn’t look like a 5250 screen; whatever you want.' [7]

Trevor Perry, an IBM Champion noted for his work with the IBM i explained part of this change to the handler process adding 'with RPG Open Access, you can consider that your handler programs are simply replacing the operating system controller programs. You can now manage the file operations to suit your specific purposes. Each of the handlers will have been written by you or a third party, and will perform a specific function.'[8]

Data types[edit]

RPG supports the following data types.[9][10]

Note:
The character in the data type column is the character that is encoded on the Definition Specification in the column designated for data type. To compare, in a language like C where definitions of variables are free-format and would use a keyword such as int to declare an integer variable, in RPG, a variable is defined with a fixed-format Definition Specification. In the Definition Specification, denoted by a letter D in column 6 of a source line, the data type character would be encoded in column 40. Also, if the data type character is omitted, that is, left blank, the default will be A if no decimal positions are specified. Otherwise, the default will be P.

Data type Name Length Description
A Alphanumeric character 1 to 16,773,104 bytes (fixed)
1 to 16,773,100 bytes (varying-length)
Alphanumeric character
B Binary numeric 1 byte (8-bit)
2 byte (16-bit)
4 bytes (32-bit)
8 bytes (64-bit)
Signed binary integer
C UCS-2 character 1 to 8,386,552 characters (fixed)
1 to 8,386,550 characters (varying)
16-bit UCS-2 character (DBCS or EGCS)
D Date 10 bytes Date: year, month, day
F Floating point numeric 4 bytes (32-bit)
8 bytes (64-bit)
Signed binary floating-point real
G Graphic character 1 to 8,386,552 characters (fixed)
1 to 8,386,550 characters (varying)
16-bit graphic character (DBCS or EGCS)
I Integer numeric 1 byte (8-bit)
2 bytes (16-bit)
4 bytes (32-bit)
8 bytes (64-bit)
Signed binary integer
N Character Indicator 1 byte '1' = TRUE
'0' = FALSE
O Object Size Undisclosed Object Reference
P Packed decimal numeric 1 to 63 digits,
2 digits per byte plus sign
Signed fixed-point decimal number with integer and fraction digits
S Zoned decimal numeric 1 to 63 digits,
1 digit per byte
Signed fixed-point decimal number with integer and fraction digits
T Time 8 bytes Time: hour, minute, second
U Integer numeric 1 byte (8-bit)
2 bytes (16-bit)
4 bytes (32-bit)
8 bytes (64-bit)
Unsigned binary integer
Z Timestamp 26 bytes Date and time:
  year, month, day, hour, minute, second, microseconds
* Basing-Pointer
Procedure-Pointer
System-Pointer
16 bytes Address to Data
Address to Activated Procedure
Address to Object

Example code[edit]

The following program receives a customer number as an input parameter and returns the name and address as output parameters.

      * Historically RPG is columnar in nature, though free-formatting
      * is allowed under particular circumstances.
      * The purpose of various lines code are determined by a
      * letter code in column 6.
      * An asterisk (*) in column 7 denotes a comment line

      * "F" (file) specs define files and other i/o devices
     F ARMstF1   IF   E       K     Disk    Rename(ARMST:RARMST)

      * "D" specs are used to define variables
     D pCusNo          S              6p 
     D pName           S             30a
     D pAddr1          S             30a
     D pAddr2          S             30a
     D pCity           S             25a
     D pState          S              2a
     D pZip            S             10a

      * "C" (calculation) specs are used for executable statements
      * Parameters are defined using plist and parm opcodes
     C     *entry        plist
     C                   parm                    pCusNo
     C                   parm                    pName
     C                   parm                    pAddr1
     C                   parm                    pAddr2
     C                   parm                    pCity
     C                   parm                    pState
     C                   parm                    pZip

      * The "chain" command is used for random access of a keyed file
     C     pCusNo        chain     ARMstF1

      * If a record is found, move fields from the file into parameters
     C                   if        %found
     C                   eval      pName  = ARNm01
     C                   eval      pAddr1 = ARAd01
     C                   eval      pAddr2 = ARAd02
     C                   eval      pCity  = ARCy01
     C                   eval      pState = ARSt01
     C                   eval      pZip   = ARZp15
     C                   endif

      * RPG makes use of switches.  One switch "LR" Originally stood for "last record"
      * LR flags the program and its dataspace as removable from memory 

     C                   eval      *InLR = *On

The same program using free calculations:

      * "F" (file) specs define files and other i/o devices
     FARMstF1   IF   E        K     Disk    Rename(ARMST:RARMST)

      * "D" specs are used to define variables and parameters
      * The "prototype" for the program is in a separate file
      * allowing other programs to call it
      /copy cust_pr
      * The "procedure interface" describes the *ENTRY parameters
     D getCustInf      PI
     D  pCusNo                        6p 0   const
     D  pName                        30a
     D  pAddr1                       30a
     D  pAddr2                       30a
     D  pCity                        25a
     D  pState                        2a
     D  pZip                         10a
      /free
        // The "chain" command is used for random access of a keyed file
        chain pCusNo ARMstF1;

        // If a record is found, move fields from the file into parameters
        if %found;
           pName  = ARNm01;
           pAddr1 = ARAd01;
           pAddr2 = ARAd02;
           pCity  = ARCy01;
           pState = ARSt01;
           pZip   = ARZp15;
        endif;

      // RPG makes use of switches.  One switch "LR" originally stood for "last record"
      // LR actually flags the program and its dataspace as removable from memory.
        *InLR = *On;
      /end-free

Assume the ARMSTF1 example table was created using the following SQL Statement:

CREATE TABLE armstf1
(arcnum DECIMAL(7,0),
 arname CHAR(30),
 aradd1 CHAR(30),
 aradd2 CHAR(30),
 arcity CHAR(25),
 arstte CHAR(2),
 arzip  CHAR(10))

The same program using free calculations and embedded SQL:

     * RPG IV no longer requires the use of the *INLR indicator to terminate a program.
     * by using the MAIN keyword on the "H" (Header) spec, and identifying the "main" or
     * entry procedure name, the program will begin and end normally without using the
     * decades-old RPG Cycle and instead a more "C like" begin and end logic.
    H  MAIN(getCustInf)
     * "D" specs are used to define variables and parameters
     * The "prototype" for the program is in a separate file
     * allowing other programs to call it
     /copy cust_pr
     * The "procedure interface" describes the *ENTRY parameters
    P getCustInf      B
    D getCustInf      PI
    D  pCusNo                        6p 0   const
    D  pName                        30a
    D  pAddr1                       30a
    D  pAddr2                       30a
    D  pCity                        25a
    D  pState                        2a
    D  pZip                         10a
     /free
       exec sql select arName, arAddr1, arAdd2, arCity, arStte, arZip
                into  :pName, :pAddr1, :pAddr2, :pCity, :pState, :pZip
                from   ARMstF1
                where  arCNum = :pCusNo
                for fetch only
                fetch first 1 row only
                optimize for 1 row
                with CS;
     /end-free
    P GetCustInf      E

As of V7R1 of the operating system, the above program would not necessarily need the prototype in a separate file, so it could be completely written as:

    H main(GetCustInf)
    D ARMSTF1       E DS
    P GetCustInf      B
    D GetCustInf      PI                  extpgm('CUS001')
    D  inCusNo                            like(arCNum) const
    D  outName                            like(arName)
    D  outAddr1                           like(arAdd1)
    D  outAddr2                           like(arAdd2)
    D  outCity                            like(arCity)
    D  outState                           like(arStte)
    D  outZip                             like(arZip)
     /free
      exec sql select arName, arAdd1, arAdd2, arCity, arStte, arZip
               into  :outName, :outAddr1, :outAddr2, :outCity, :outState,
                     :outZip
               from   ARMSTF1
               where  arCNum = :inCusNo
               fetch first 1 row only
               with CS
               use currently committed;
     /end-free
    P GetCustInf      E

Platforms[edit]

As stated above, the RPG programming language originally was introduced by IBM for their proprietary 1401, /360, /3, /32, /34, /36, /38 AS/400 and System i systems. There have also been implementations for the Digital VAX, Sperry Univac BC/7, Univac system 80, Siemens BS2000, Burroughs B700, B1700, Hewlett Packard HP3000, ICL 2900 series, Honeywell 6220 and 2020, Four-Phase IV/70 and IV/90 series, Singer System 10 and WANG VS, as well as miscellaneous compilers & runtime environments for Unix-based systems (INFINITE 36 (formerly UNIBOL36)) and PCs (Baby/400, Lattice-RPG).

The latest platform to receive an RPG compiler is Windows .Net through the WINRPG compiler which was purchased by I-Net System Solutions in March 2013. This version contains extensions to RPG IV beyond that of the base IBM compiler. These extensions provide Windows and .Net hooks in the Native and System 36 environment, as well as the ability to port DB/2 files to Access and SQL ODBC databases.

RPG II applications are still supported under the IBM z/VSE and z/OS operating systems, HP MPE operating system on HP3000 and the OpenVMS operating system on VAX, Alpha, and Unisys MCP and now Windows Servers and Desktops under I-Net RPG.

References[edit]

  1. ^ http://publib.boulder.ibm.com/infocenter/iadthelp/v7r0/index.jsp?topic=/com.ibm.etools.iseries.pgmgd.doc/c092507618.htm
  2. ^ "...IBM 1401 and the Report Program Generator (RPG) contributed significantly to this success...", IBM 1401 Data Processing System / 1959
  3. ^ "Generating Random Numbers in ILE RPG Using the CEERAN0 API", IBM.com
  4. ^ Paris, Jon; Gantner, Susan. "Totally Free RPG". IBM Systems Magazine. Retrieved 8 March 2014. 
  5. ^ "IBM RPG/400 User’s Guide". 
  6. ^ CGIDEV2 home
  7. ^ You and i: You and i 7.1. Ibmsystemsmag.blogs.com (2010-04-13). Retrieved on 2013-08-10.
  8. ^ Trevor Perry | looksoftware blog. Looksoftware.com. Retrieved on 2013-08-10.
  9. ^ "RPG/400 Reference". IBM. June 1994. 
  10. ^ "RPG/400 User's Guide". IBM. June 1994. 

Further reading[edit]

External links[edit]