Object REXX

Object REXX

Paradigm	Multi-paradigm: object-oriented (class-based), procedural (imperative), structured
Designed by	Simon C. Nash (IBM)
First appeared	1988 (1988)
Stable release	5.0.0 / 10 May 2023 (10 May 2023)
Preview release	5.1.0
Implementation language	C++
Platform	IA-32, x86-64, ARM, s390x
OS	Cross-platform: Linux, Microsoft Windows, macOS, Solaris, OpenIndiana, AIX, FreeBSD, OS/2
License	CPL 1.0, GPLv2
Filename extensions	.rxs, .rex, .rexx, .cls
Website	www.rexxla.org
Major implementations
Object REXX (until 2004) ooRexx (since 2005)
Influenced by
Rexx, Smalltalk
Influenced
NetRexx

Object REXX is a high-level, general-purpose, interpreted, object-oriented (class-based) programming language.

It is a follow-on and a significant extension of the Rexx programming language (often called "Classic Rexx"). Object REXX retains all the features and syntax of "Classic Rexx" while adding full object-oriented programming (OOP) capabilities. Although Object REXX does not implement all aspects of the "Information Technology – Programming Language REXX" ANSI X3.274-1996 standard, it offers many new features of its own.

Following its "Classic Rexx" influence, Object REXX is designed to be easy to learn, use, and maintain. Several object-oriented implementations of REXX are available, including Open Object Rexx ("ooRexx") and Rexx Object Oriented ("roo!").

History

In 1988, the "Oryx" project at IBM, under the technical direction of Simon C. Nash, experimented with merging "Classic Rexx" with the object model of Smalltalk. The motivation behind the project was to transfer the advantages of OOP to "Classic Rexx" while remaining compatible and thus transferring the usability of "Classic Rexx" to OOP. Early on, the projects focused on OOP aspect such as treating everything as an object, object-based encapsulation and message passing, object-based concurrency, classes and inheritance.

This initial work later led under the direction of Rick McGuire to the first prototype of Object REXX, which was presented in 1992. In 1994, IBM announced that Object REXX would replace "Classic Rexx" as the standard REXX interpreter in the next version of OS/2. In 1996, Object REXX was released as part of the OS/2 Warp 4 operating system. In 1997, versions for Windows 95, Windows NT and Linux followed. In 1999 an Object REXX version for AIX V4.1.5 or higher was released. In 2000, versions for zLinux and Sun/Solaris followed. For Windows 2000, Windows Me, Windows 98 and Windows NT 4.0, the last major update for Object REXX was released in 2001.

On 12 October 2004, IBM announced the discontinuation of Object REXX and transferred the source code and licensing rights to the non-profit Special Interest Group (SIG), the Rexx Language Association (RexxLA). The code that IBM released to open source did not include the classes for IBM System Object Model (SOM) and Workplace Shell (WPS) support. The OS/2 version of Object REXX includes classes to support SOM and WPS. These are also included OS/2's initial follow-on product, eComStation, and also in its current descendant, ArcaOS, for which IBM's original Object REXX interpreter continues to be available.

In 2005, the RexxLA released ooRexx as a new incarnation of Object REXX as free and open-source software under the Common Public License. This first version of ooRexx 3.0.0 has been heavily refactored compared to the original IBM source code in order to increase readability. Later, the ooRexx kernel was rewritten in pure C++, and a new architecture and native interface were designed and implemented under the technical direction of Rick McGuire. This work enabled the RexxLA to release ooRexx 4.0.0 with support for 64-bit in 2009. To this day, the RexxLA continues to develop, support and maintain ooRexx as well as "Classic Rexx" and NetRexx. Furthermore, the RexxLA organizes annual symposia.

Releases

The following table contains noteworthy features and changes of major Object REXX and ooRexx interpreter versions. All ooRexx releases and the necessary documentation are available on Sourceforge. For Arch Linux based distributions the current and the development version are available as Arch User Repository. For ooRexx 5.0.0 an unofficial port to OS/2 is available. Since release 5.0.0, portable versions of the interpreter are available that allow it to be used without installation. For Intellij IDEA, the ooRexxPlugin adds support for syntax highlighting, syntax checking, code completion and documentation support modeled after Javadoc using annotations.

Legend:

Old version

Old version, still maintained

Latest version

Latest preview version

Future release

Major Releases	Release Date	Notable Features and Changes
Old version, no longer maintained: Object REXX 1.0.0 (OS/2)	1996-09-25	First official release as part of OS/2 Warp 4
Old version, no longer maintained: Object REXX 1.0.0 (Windows)	1997-02-28 (IE) 1997-05-30 (DE)	First releases for Windows as "Interpreter Edition" (IE) and "Development Edition" (DE) DE additionally provides a dialogue class library, a graphical dialogue editor and a built-in tokeniser Provides structured programming constructs such as select, do loops, if-then-else branching and subroutine calls Provides array handling, arithmetic and other build-in functions Support for OOP concepts such as classes, object, methods, encapsulation, messaging, polymorphism, inheritance and multiple inheritance (metaclasses and mix-in classes) Includes interfaces to DB2, TCP/IP sockets and C/C++ applications
Old version, no longer maintained: Object REXX 1.1.0 (AIX)	1999-04-09	First release for AIX V4.1.5 Addition of an interface to the file transfer protocol
Old version, no longer maintained: Object REXX 2.1.0 (Windows)	2001-04-21	Support for Windows 98, Windows Me, Windows 2000, and Windows NT Support for Object Linking and Embedding/ActiveX, Windows Script Host (WSH) engine Support for Unicode functions and addition of mathematical function package Support for subroutine, procedure and function calls Support for stems and compound variables
Old version, no longer maintained: ooRexx 3.0.0	2005-03-30	First release of ooRexx as the open-source successor to Object REXX Supports 28 keyword instructions, four directives, 29 classes with associated methods and 75 build-in functions ooDialog 3.0.0 for creating graphical user interfaces on Windows systems Includes extension classes for mathematical calculation, dealing with TCP/IP sockets, regular expressions and the file transfer protocol Improved PDF documentation that supports links, meta information and document indexing
Old version, no longer maintained: ooRexx 3.1.0	2006-08-21	Various enhancements Separate documentation for ooDialog
Old version, no longer maintained: ooRexx 3.1.1	2006-11-23	Support for Linux, Windows, AIX and Solaris Additional functions for the RexxUtil library Additional methods for several classes Addition of CircularQueue class and associated methods
Old version, no longer maintained: ooRexx 3.1.2	2007-09-17	Added support for MacOS Additional methods for the MutableBuffer, String and Object classes Provides interface to Open Office
Old version, no longer maintained: ooRexx 3.2.0	2008-01-22	Several enhancements
Old version, no longer maintained: ooRexx 4.0.0	2009-09-30	Support for 64bit versions of Linux, AIX and Windows Improved C++ application programming interface Restructuring of ooDialog and addition of 7 classes and 24 methods Addition of Buffer, IdentityTable, Orderable, Package, Pointer, RexxContext, Routine, WeakReference and SocketClass classes and associated methods Addition of 17 samples to illustrate ooRexx concepts Separate documentation for Windows extension library Four new methods for the RexxQueue, three for the Object, four for the DateTime and one each for the Method, Stem and String classes The MutableBuffer class now supports most of the String class methods Addition of seven methods to the OLEObject class, responsible for the Object Linking and Embedding/ActiveX interface Drop support for the Windows Script Host (WSH) engine
Old version, no longer maintained: ooRexx 4.1.0	2011-09-28	Addition of File class including four new methods and 29 instance methods Addition of extension library for Unix systems (49 functions) Separate documentation for Rexx extensions library and Unix extensions library Addition of extension classes for handling the comma-separated values, multipurpose internet mail extensions and simple mail transfer protocol Addition of ooSQLite extension to create, modify, and query SQL based databases Enhancement of TCP/IP socket support Additional class and method for ooDialog Additional method for DateTime class
Old version, no longer maintained: ooRexx 4.2.0	2014-02-23	More than 43 enhancements Standalone installer for ooDialog 4.2.3 and several new classes and methods Separate documentation for ooSQLite external library Systemd support for Linux system and compliance with Linux Standard Base Add trace information about method invocations Additional method each for the String, Mutablebuffer, StackFrame, Queue and OrderedCollection classes Additional methods for the Relation class, several sorting methods for OrderedCollections and methods for inserting and deleting elements for the Array class
Current stable version: ooRexx 5.0.0	2022-12-22	A total of 86 new features and 76 enhancements Addition of several new keyword instructions and directives A total of 57 classes and associated methods Addition of AlarmNotification, Json, MessageNotification, RexxInfo, StringTable, StringTable and Validate classes and associated methods Additional methods for Alarm, Class, Collection, Directory, Message, Method, MutableBuffer, Object, Package, Routine, String and RxFtp classes Separate documentation for a) ooRexxUnit (unit testing framework), b) using ncurses for writing text-based user interfaces, c) the C++ application programming interfaces and d) explaining the release and build environment
Latest preview version of a future release: ooRexx 5.1.0	2024-09-19

Design philosophy

ooRexx follows the design philosophy of "Classic Rexx" to create a "human-centered" programming language that is easy to learn, code, remember and maintain. This is achieved, in part, by keeping the language small and following the principle of least astonishment. A readable syntax is enabled by being case-insensitive, free-form, requiring as little punctuation as possible, and using instructions that are straightforward English. In addition, it is a dynamic programming language that offers flexibility and allows to focus on development rather than language constraints. There is only one data type, the character string, which does not have to be declared, thereby reduces the effort for programmers compared to strictly typed languages.

Following the "documentation before implementation" design principle of “Classic Rexx”, ooRexx offers comprehensive documentation in accordance with the IBM Style Guide that includes syntax diagrams and examples.

Instructions

As in "Classic Rexx", there are assignment instructions, keyword instructions and command instructions, and in ooRexx there are also the directive instructions. In line with the desire to keep the language small, there are only thirty keyword instructions in ooRexx 5.0.0. Unlike many other languages, no keywords are reserved, so there is no need to memorize a long list of reserved words. In cases where the string is neither an assignment nor a keyword instruction, it is considered a command instruction, which causes the interpreter to pass it to the operating system for execution and set a variable RC for the return code. In addition, the ADDRESS instruction allows commands to be redirected to specific environments such as Bourne Shell, Bash, Z-Shell, Command Prompt and others, as well as intercepting errors.

a = "hello world"               /* assignment instruction       */
do i = 1 to 2                   /* keyword instruction "DO"     */
    say "round #" i":" a        /* keyword instruction "SAY"    */
end                             /* keyword instruction "END"    */
"echo Hello World"              /* command to operating system  */
say "RC:" rc                    /* return code                  */

Free-form

ooRexx has a free-form syntax where the positioning of the program code is irrelevant, which allows a high degree of flexibility. Before execution, the interpreter merges multiple unquoted blanks into one, while a character string enclosed in quotation marks (single or double) is not changed. Concatenation can be requested explicitly with two vertical bars (||), or implicitly by separating terms with spaces or by abutting terms. Optionally, clauses can be spread over several lines by using the comma (,) or the minus sign (-) as a continuation character, or several clauses can be used in a single line, separated by a semicolon (;). Since a free-form language provides flexibility and requires fewer syntactic rules to be considered, it is assumed that it eases the learning effort by reducing the intrinsic cognitive load.

say   "Hello World!"                   /* output: Hello World!        */
say "   This"     'is' -               /* minus sign for continuation */
        "REXX"   || "!"                /* output:    This is REXX!    */

Case-insensitive

As "Classic Rexx", ooRexx is a case-insensitive programming language. The interpreter capitalizes all characters outside quotation marks before executing them. Because the cases do not need to be differentiated, fewer additional details need to be learned and frustrating syntax errors are avoided.

a = "This is REXX!"
Say A                                 /* output: This is REXX!  */
SAY a                                 /* output: This is REXX!  */

Message paradigm

Similar to the messaging paradigm implemented by Alan Kay in Smalltalk, everything in ooRexx is an object that can be communicated with by sending messages naming a method. The notion of sending messages to objects as if they were living beings helps beginners to learn OOP concepts.

In contrast to Smalltalk, there is an explicit message operator, the tilde (~), where the receiving object is placed to the left of it and the result of the operation is returned. Like Smalltallk, ooRexx messages can be cascaded if two tildes (~~) are used instead of one, returning the object that received the method rather than the result produced. The default behavior of most methods can be changed by specifying an option, which can be either spelled out or abbreviated and is not case-sensitive. This enables a literal understanding and reduces the learning effort for beginners. For example the strip method by default removes leading and trailing blanks. This behavior can be changed, for example, by specifying "leading" or "l" as an option. While functions are nested in "Classic Rexx", messages can be chained in ooRexx, which improves the readability of a statement.

a = "   I am ooRexx!"
say a                                 /* output:    I am ooRexx! */
say a~Strip("Leading")                /* output: I am ooRexx!    */
say a~strip("l")~reverse              /* output: !xxeRoo ma I    */

Features

ooRexx is designed to retain all the features of "Classic Rexx". Its conforms to the ANSI standard for the Rexx language (X3.274-1996, “Programming Language Rexx”), for interoperability across platforms with other conforming implementations. Thus "Classic Rexx" programs typically run under ooRexx without any changes. This makes it easy to transport both program code and developer knowledge from "Classic Rexx" to ooRexx. To this, ooRexx adds all the features of OOP, such as subclassing, polymorphism, and data encapsulation. Further features include multiple inheritance via mixin classes.

Parsing

The PARSE keyword instruction makes it possible to quickly and flexibly parse a string and assign parts of it to variables in a single step. Subsequent instruction is used to specify the source of the string, for example ARG for arguments that are listed when the program or function is called, VAR for variables, PULL for data queues or standard input (typically the keyboard), VALUE for any expression. When using VALUE, the WITH keyword is required to specify the end of an expression, followed by a parsing pattern. This pattern can be a list of variables, a position number or literal delimiters; it is possible to use these patterns in combination. Optionally, the upper and lower case of the string can be converted before parsing.

aString = "Person: Rick McGuire" 
parse value aString with type ":" first second     /* delimiter & variable list */
say first second                                   /* output: Rick McGuire      */

Classes and Methods

In addition to the three instruction types of "Classic Rexx", ooRexx adds directive instruction that are not executable, with the first directive marking the end of the executable part of a program. To make directive instructions readily recognizable, they are introduced with two consecutive colons (::). The ::CLASS directive causes the interpreter to define a new class, and the ::METHOD directive to define a new method. The ::ATTRIBUTE directive is used to define an accessor method that can retrieve or assign an object variable. With the EXPOSE instruction, the object variable is exposed to a method, while PARSE can be used to parse the parameter and assign it to a variable.

d = .dog~new("Bella")                                   /* create and assign a dog  */
d~bark                                                  /* send bark message        */
say d~name                                              /* output: Bella            */

::class dog                                             /* class directive          */
  ::Attribute name                                      /* attribute directive      */
::method init                                           /* object initiation method */
  Expose name                                           /* exposes name of dog      */
  Parse arg name                                        /* assigns "Bella" to name  */
::method bark                                           /* method directive         */
  Expose name
  say Name "goes woof!"                                 /* output: Bella goes woof! */

There are four different types of classes: Object classes, that act as a factory for creating objects, mixin classes which add methods to other classes, abstract classes to provide definitions for methods, and metaclasses that can be used to create other classes.

The ooRexx interpreter offers built-in classes and associated methods and functions that perform various text and number processing, search and comparison operations, formatting capabilities and arithmetic calculations.

Built-in functions

In addition to the built-in classes, ooRexx 5.0.0 provides 82 built-in functions, including character manipulation, conversion, and information functions, many of which call methods of the String class. The built-in dynamic link library RexxUtil offers 29 cross-platform, 25 Windows-specific and four Unix-specific functions for manipulating system files, directories, classes and objects.

Multi-threading

Conceptually, ooRexx provides object-based concurrency, according to which objects have independent resources to execute methods and can communicate with each other using the messaging paradigm. Several objects can be active at the same time and exchange messages for synchronization. Concurrency can be achieved either with the REPLY keyword instruction, which causes an early return from a method while its remainder continues to execute in a new thread, with the GUARD keyword instruction, which can set a method as unguarded so that it can execute together with other methods of the same class, or by using the start method of the Object class, which causes the receiver to process the message in a separate thread.

Tracing

As in “Classic Rexx”, the TRACE keyword instruction and the built-in TRACE() function facilitate debugging, allow for control of the level of detail and enable interactive debugging at runtime. When interactive debugging, the interpreter pauses after most instructions that are traced. While multi-threaded programs can be traced, ooRexx 5.1.0 introduces as an addition the TraceObject class, which provides additional information such as the interpreter instance, the number of the thread on which the message is dispatched, and the state of the guard locks, allowing to judge which method is currently blocked.

External libraries

Using the ::REQUIRES directive, external function packages can be integrated on a per program basis. This directive is placed after the main code section and allows access either to public classes and routines of a Rexx program or, by specifying the LIBRARY option, to external libraries. Such libraries are usually organized around domain-specific functions.

The Rexx extension library provides a class for reading and writing comma-separated values (CSV) files, for creating and processing JavaScript Object Notation (JSON) data and a sub-command environment that partially emulates a TSO/CMS environment. The RxSock library enables to incorporate TCP/IP protocols, while the RxFtp library specifically provides access to the file transfer protocol. The RxMath library offers advanced mathematical functions such as square root calculation, exponential function, logarithm, sine, cosine, tangent, arc sine and power calculation.

Say rxcalcsin(1)                /* output: 0.0174524064 */

::requires 'rxmath' LIBRARY

For Windows, ooRexx includes the OODialog framework allowing to produce Windows dialogs and therefore graphical user interfaces. The ooRexx interpreter is delivered with several example programs and function packages that demonstrate the use of this framework.

For POSIX-compatible operating systems, the nCurses class library enables the writing of text-based user interfaces using the ncurses programming library. The RxUnixSys library provides functions on most Unix systems for interacting with processes and threads, users and user groups, files and file systems and other.

Bridges

While ooRexx compared to Object REXX no longer contains classes for SOM and WPS support, it offers application programming interfaces (APIs) for interacting with code written in C or C++. Furthermore, classes are provided that enable the automation of Windows applications. The ooSQLite class provides an interface to SQLite, an in-process library that implements a self-contained, serverless, zero-configuration, transactional SQL database engine. There is also an external library that implements a bidirectional Java bridge, based on the Bean Scripting Framework, called BSF4ooRexx, which allows Java classes to be used in ooRexx programs.

C/C++ APIs

As "Classic Rexx", ooRexx includes APIs for extending Rexx applications with programs written in C and vice versa. This includes the creation of handlers for subcommands used in Rexx programs that run as application macros, external functions that allow a direct extension of the ooRexx function set and system functions that allow the behavior of the interpreter to be customized.

In addition, APIs are available that allow C++ applications to extend ooRexx and vice versa. This includes handlers for methods and functions written in C++ that extend ooRexx, both packaged as external libraries. These libraries are packaged as dynamic link libraries on Windows or as shared libraries on Unix-based systems. An external library can be loaded with the ::REQUIRES directive or by using the EXTERNAL keyword instruction as part of a ::ROUTINE, ::METHOD, or ::ATTRIBUTE directive.

Windows automation

The Windows extension includes the Windows Script Host (WSH) Scripting Engine that can be used to perform general automation tasks. It also includes Object Linking and Embedding/ActiveX (OLE) support allowing to interact with Windows programs via the OLEObject. OLE Automation is an inter-process communication mechanism developed by Microsoft that is based on a subset of the Component Object Model (COM) and enables, among other things, the invocation of program functions, the querying and setting of attributes and the interception of component events. The ooRexx interpreter includes examples that demonstrate some features of WSH, interaction with Access, Word, Excel and other programs via OLE, and a utility to browse available OLE objects.

excelApplication = .OLEObject~new("Excel.Application")    /* create object for Excel */
excelApplication~visible = .true                          /* make Excel visible      */
Worksheet = excelApplication~Workbooks~Add~Worksheets[1]  /* add worksheet           */
Worksheet~cells(1,1)~Value = “First Cell”                 /* insert string into cell */

In addition to OLE support, the Windows extension enables interaction with the Windows program manager, the system event log, the clipboard and the registry as well as to query, edit and interact with windows, menus or sub-menus.

See also

• Comparison of programming languages
• Timeline of programming languages
• REXX
• NetRexx

Further reading

• Ashley, W. David; Flatscher, Rony G.; Hessling, Mark; McGuire, Rick; Peedin, Lee; Sims, Oliver; Wolfers, Jon (2022). ooRexx Documentation 5.0.0 Open Object Rexx Reference (PDF). RexxLA.
• Ashley, W. David; Flatscher, Rony G.; Hessling, Mark; McGuire, Rick; Peedin, Lee; Sims, Oliver; Wolfers, Jon (2022). ooRexx Documentation 5.0.0 Programmer Guide (PDF). RexxLA.
• Ashley, W. David; Flatscher, Rony G.; Hessling, Mark; McGuire, Rick; Peedin, Lee; Sims, Oliver; Sims, Oliver; Wolfers, Jon (2022). ooRexx Documentation 5.0.0 Windows Extensions Reference (PDF). RexxLA.
• Ashley, W. David; Flatscher, Rony G.; Hessling, Mark; McGuire, Rick; Peedin, Lee; Sims, Oliver; Wolfers, Jon (2022). ooRexx Documentation 5.0.0 Application Programming Interfaces (PDF). RexxLA.

External links

• Rexx Language Association
• Open Object Rexx 5.0.0 documentation
• Open Object Rexx on Sourceforge
• Open Object Rexx Website
• Open Object Rexx on Rosetta Code