Modula-2 (ModulaTwo) is the 2nd of the ModulaLanguage''''''s, thus one of the WirthLanguages.  It was a refinement of the original Modula (ModulaOne), which was derived from Pascal (PascalLanguage).  Modula-2 is the ancestor of Modula-3 (ModulaThree) and Oberon (OberonLanguage).  Wirth used it to develop the Lilith workstation in the late seventies.  He was inspired during his 1976 sabbatical leave at XeroxParc by Mesa (MesaLanguage), which was also an extension of Pascal.

'''Main differences to Pascal'''
* Module concept for separate compilation of independent program units
* Name spaces, with qualified and unqualified identifiers, tied to modules
* Encapsulation with separation of interface and implementation, tied to modules
* Procedure types
* Unsigned integer type (CARDINAL)
* Explicit type conversion (safe) and type casting (unsafe) required
* I/O via modules instead of built-in language support
* Pseudo module SYSTEM for accessing system dependent resources
** Machine dependent types BYTE, WORD, ADDRESS
** Built-in coroutine support for concurrency: PROCESS, NEWPROCESS, TRANSFER, IOTRANSFER

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'''Dialects of Modula-2'''
* PIM2, language report published in the 2nd edition of Wirth's "Programming in Modula-2"
* PIM3, minor revision of PIM2, published in the 3rd edition of Wirth's "Programming in Modula-2"
* PIM4, minor revision of PIM3, published in the 4th edition of Wirth's "Programming in Modula-2"
* ISO 10514-1, specification published by the International Standards Organisation (ISO)
* R10, language revision of 2010 based on PIM, authored by two former ISO WG participants

ISO 10514-1 clarified some ambiguities and added structured literals, a complex number type, exception handling, module finalisation and a standard library.

'''Supersets of Modula-2'''
* PIM supersets
** Modula-2+, developed at DigitalEquipmentCorporation, adding preemptive threads, garbage collections and exception handling
** Modula-2*, adding support for parallel computing
** Modula-P, another parallel extension
** Modula-Prolog, adding a Prolog layer
** Modula-2/R, adding support for relational databases
** Objective Modula-2 (ObjectiveModulaTwo), adding a Smalltalk derived OOP layer for native support of Cocoa and GNUstep
* ISO supersets
** ISO10514-2, adding an OOP layer
** ISO10514-3, adding a generics layer
** Mod51, adding an IEC1132 layer for embedded systems development

'''Derivatives of Modula-2'''
* Modula-3 (ModulaThree), developed by former Xerox PARC employees at DigitalEquipmentCorporation and Olivetti
* Oberon (OberonLanguage), developed by Niklaus Wirth for the Oberon operating system
* Oberon-2, revision of Oberon with support for object oriented programming
* Umbriel, a teaching language by Pat Terry

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'''Modula-2 Books'''
* Niklaus Wirth 1982: ''Programming in Modula-2''. Springer-Verlag: Berlin, ISBN 3-540-11674-5; New York, ISBN 0-387-11674-5.
* Gary Ford & Richard Wiener 1985: ''Modula-2: A Software Development Approach''. John Wiley & Sons Inc. 416 pp. ISBN-0-471-87834-0.

'''Modula-2 Compilers'''
* Actively developed/maintained
** ACK Modula-2, part of the Minix operating system, open source
** Aglet Modula-2, for AmigaOS 4.0, PPC only, freeware
** GNU Modula-2, a GCC front-end, cross-platform, open source
** Mod51, targeting 80C51 micro-controllers, for embedded systems development, commercial
** Modula2JCC, a compiler written in Java, graduation project, open source
** Modulaware Modula-2, for OpenVMS, both Alpha and VAX, commercial
** Objective Modula-2, targeting C and LLVM, cross-platform, open source
** p1 Modula-2, for Macs, generates PPC assembly and C source, but Carbon only, commercial

* No longer maintained but still available
** Canterbury Modula-2, generates Java source, cross-platform, commercial
** Logitech/Multiscope Modula-2, for MS-DOS, commercial
** M2VMS by Terra, for OpenVMS, both Alpha and VAX, commercial
** MOCKA Modula-2, for Linux and 386BSD, freeware
** XDS Modula-2, for Linux and Windows, x86 or targeting C, freeware

* No longer available but of historic interest
** Stony Brook Modula-2 was available for MS-DOS and Windows
** TopSpeed Modula-2 was available for MS-DOS and Windows
** Volition Systems Modula-2 was available for many platforms, targeting the UCSD-p virtual machine, a predecessor of Java's JVM

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'''Active Modula-2 Projects'''
* The Aglet Modula-2 project at http://home.ntelos.net/~tbreeden
* The GNU Modula-2 project at http://gnu.modula2.net
* The Modula2jcc home page: http://code.google.com/p/modula2jcc
* The Objective Modula-2 project at http://objective.modula2.net

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'''Modula-2 Online Resources'''

* Modula-2 FAQ at http://faq.modula2.net
* Modula-2 Freepages at http://freepages.modula2.org
* Modula-2 Resource page at http://www.modula2.net
* Modula-2 Web Directory at http://www.modula2.org
* List of Modula-2 compilers at http://www.modula2.net/resources/compilers.shtml
* List of Modula-2 books at http://www.modula2.net/resources/books.shtml
* Usenet news groups comp.lang.modula2 at http://groups.google.com/group/comp.lang.modula2

'''Modula-2 IRC chat'''
* irc://irc.freenode.org/#modula-2

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CategoryProgrammingLanguage CategoryPascal ModulaLanguage