Ada programming language

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Ada is a structured, statically typed imperative computer programming language designed by a team led by Jean Ichbiah of CII Honeywell Bull during 19771983. It addresses many of the same tasks as C or C++, but with the type-safety of a language like Java. (Some cite Ada as an influence on Java.) Ada was named after Ada Lovelace, often credited as the first computer programmer.

Features

Ada was originally targeted at embedded and real-time systems, and is still commonly used for those purposes. The Ada 95 revision, designed by S. Tucker Taft of Intermetrics between 1992 and 1995, improved support for systems, numerical, and financial programming.

Notable features of Ada include strong typing, modularity mechanisms (packages), run-time checking, parallel processing (tasks), exception handling, and generics. Ada 95 added support for object-oriented programming, including dynamic dispatch.

Ada supports run-time checks in order to protect against access to unallocated memory, buffer overflow errors, off by one errors, array access errors, and other avoidable bugs. These checks can be disabled in the interest of efficiency, but can often be compiled efficiently. It also includes facilities to help program verification. For these reasons, it is very widely used in critical systems like avionics, weapons and spacecraft.

It also supports a large number of compile-time checks to help avoid bugs that would not be detectable until run-time in some other languages or would require explicit checks to be added to the source code.

Ada's dynamic memory management is safe and high-level, like Java and unlike C. The specification does not require any particular implementation. Though the semantics of the language allow automatic garbage collection of inaccessible objects, most implementations do not support it. Ada does support a limited form of region-based storage management. Invalid accesses can always be detected at run time (unless of course the check is turned off) and sometimes at compile time.

The Ada language definition is unusual among ISO standards in that it is free content. One result of this is that the standard document (known as the Ada Reference Manual or ARM) is the usual reference Ada programmers resort to for technical details, in the same way as a particular standard textbook serves other programming languages.

History

In the 1970s, the US Department of Defense (DoD) was concerned by the number of different programming languages being used for its projects, many of which were obsolete or hardware-dependent, and none of which supported safe modular programming. In 1975 the Higher Order Language Working Group (HOLWG) was formed with the intent of reducing this number by finding or creating a programming language generally suitable for the department's requirements; the result was Ada. The total number of high-level programming languages in use for such projects fell from over 450 in 1983 to 37 by 1996.

Template:Wikisourcepar The working group created a series of language requirements documents—the Strawman, Woodenman, Tinman, Ironman and Steelman documents. Many existing languages were formally reviewed, but the team concluded in 1977 that no existing language met the specifications.

Requests for proposals for a new programming language were issued and four contractors were hired to develop their proposals under the names of Red (Intermetrics led by Benjamin Brosgol), Green (CII Honeywell Bull, led by Jean Ichbiah), Blue (SofTech, led by John Goodenough), and Yellow (SRI International, led by Jay Spitzen ). In April 1978, after public scrutiny, the Red and Green proposals passed to the next phase. In May of 1979, the Green proposal, designed by Jean Ichbiah at CII Honeywell Bull, was chosen and given the name Ada—after Augusta Ada, Countess of Lovelace. This proposal was influenced by the programming language LIS that Ichbiah and his group had developed in the 1970s. The preliminary Ada reference manual was published in ACM SIGPLAN Notices in June 1979. The Military Standard reference manual was approved on December 10, 1980 (Ada Lovelace's birthday), and given the number MIL-STD-1815 in honor of Ada Lovelace's birth year.

In 1987, the US Department of Defense began to require the use of Ada (the Ada mandate) for every software project where new code was more than 30% of result, though exceptions to this rule were often granted. This requirement was effectively removed in 1997, as the DoD began to embrace COTS (commercial off-the-shelf) technology. Similar requirements existed in other North Atlantic Treaty Organisation countries.

Because Ada is a stongly-typed language, it has been used outside the military in commercial aviation projects, where a software bug can mean fatalities. The fly-by-wire system in the Boeing 777 runs software written in Ada.

The language became an ANSI standard in 1983 (ANSI/MIL-STD 1815A, and without any further changes became an ISO standard in 1987 (ISO-8652:1987). This version of the language is commonly known as Ada 83, from the date of its adoption by ANSI, but is sometimes refered also as Ada 87, from the date of its adoption by ISO.

Ada 95, the joint ISO/ANSI standard (ISO-8652:1995) is the latest standard for Ada. It was published in February 1995 (making Ada 95 the first ISO standard object-oriented programming language). To help with the standard revision and future acceptance, the US Air Force funded the development of the GNAT Compiler. Nowadays the GNAT Compiler is part of the GNU Compiler Collection.

Work continues on improving and updating the technical content of the Ada programming language. A Technical Corrigendum to Ada 95 was published in October 2001. Presently, more work is being done to produce the roughly once-a-decade major update to Ada, expected in late 2006 (see official schedule). This new version is commonly known as Ada 2005, just as Ada95 was commonly known as Ada94 prior to its publication.

"Hello, world!" in Ada

A common example of a language's syntax is the Hello world program:

with Ada.Text_IO; 

procedure Hello is
begin
   Ada.Text_IO.Put_Line("Hello, world!");
end Hello;

There are shortcuts available for Ada.Text_IO.Put_Line, needing less typing, however they are not used here for better understanding. For a detailed explanation see Wikibooks:Ada Programming/Basic.

The Ariane 5 failure

A commonly encountered myth blames the loss of Ariane 5 Flight 501, a European Space Agency Ariane 5 rocket, on a bug in an Ada program or on disabling Ada's runtime checks. For the Ariane 4 it had been proven that those runtime checks weren't needed. Although range checks and appropriate exception handlers on all type conversions might have trapped the problem, the problem itself was a design decision to reuse a part and its software from the Ariane 4 rocket without adequate analysis of its suitability or tests on Ariane 5 data.

See also

Online tutorials

Ada has always been a very open language, and there are many online tutorials available. The following sites have link collections to Ada tutorials

Organizations

Compilers

Tools

Related programming languages

  • SPARK - High integrity language based on an Ada subset
  • VHDL

Related topics

References

International Standards

Books

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Wikibooks has more about this subject:
  • Jan Skansholm: Ada 95 From the Beginning, Addison-Wesley, ISBN 0-201-40376-5
  • John Barnes: Programming in Ada plus Language Reference Manual, Addison-Wesley, ISBN 0-201-56539-0
  • John Barnes: Programming in Ada 95, Addison-Wesley, ISBN 0-201-34293-6
  • John Barnes: High Integrity Ada: The SPARK Approach, Addison-Wesley, ISBN 0201175177
  • John Barnes: High Integrity Software: The SPARK Approach to Safety and Security, Addison-Wesley, ISBN 0-321-13616-0
  • Dean W. Gonzalez: Ada Programmer's Handbook, Benjamin-Cummings Publishing Company, ISBN 0805325298
  • M. Ben-Ari: Ada for Software Engineers, John Wiley & Sons, ISBN 0-471-97912-0
  • Norman Cohen: Ada as a Second Language, McGraw-Hill Science/Engineering/Math, ISBN 0-0-7011607-5
  • Alan Burns, Andy Wellings: Real-Time Systems and Programming Languages. Ada 95, Real-Time Java and Real-Time POSIX., Addison-Wesley, ISBN 0-201-72988-1
  • Alan Burns, Andy Wellings: Concurrency in Ada, Cambridge University Press, ISBN 0-521-62911-X
  • Colin Atkinson: Object-Oriented Reuse, Concurrency and Distribution: An Ada-Based Approach, Addison-Wesley, ISBN 0201565277
  • Grady Booch, Doug Bryan: Software Engineering with Ada, Addison-Wesley, ISBN 0805306080
  • Daniel Stubbs, Neil W. Webre: Data Structures with Abstract Data Types and Ada, Brooks Cole, ISBN 0-534-14448-9
  • Pascal Ledru: Distributed Programming in Ada with Protected Objects, Dissertation.com, ISBN 1-58112-034-6
  • Fintan Culwin: Ada, a Developmental Approach, Prentice Hall, ISBN 0132646803
  • John English, Fintan Culwin: Ada 95 the Craft of Object Oriented Programming, Prentice Hall, ISBN 0-1-3230350-7
  • David A. Wheeler: Ada 95, Springer-Verlag, ISBN 0-387-94801-5
  • David R. Musser, Alexander Stepanov: The Ada Generic Library: Linear List Processing Packages, Springer-Verlag, ISBN 0387971335
  • Michael B. Feldman: Software Construction and Data Structures with Ada 95, Addison-Wesley, ISBN 0201887959
  • Simon Johnston: Ada95 for C and C++ Programmers, Addison-Wesley, ISBN 0201403633
  • Michael B. Feldman, Elliot B. Koffman: Ada 95, Addison-Wesley, ISBN 0-201-36123-X
  • Nell Dale, Chip Weems, John McCormick: Programming and Problem Solving with Ada 95, Jones & Bartlett Publishers, ISBN 0763702935
  • Nell Dale, Susan Lilly, John McCormick: Ada Plus Data Structures: An Object-Based Approach, Jones & Bartlett Publishers, ISBN 0669416762
  • Bruce C. Krell: Developing With Ada: Life-Cycle Methods, Bantam Dell Pub Group, ISBN 0553091026
  • Judy Bishop: Distributed Ada: Developments and Experiences, Cambridge University Press, ISBN 0-521-39251-9
  • Bo Sanden: Software Systems Construction With Examples in Ada, Prentice Hall, ISBN 013030834X
  • Bruce Hillam: Introduction to Abstract Data Types Using Ada, Prentice Hall, ISBN 0130459496
  • David Rudd: Introduction to Software Design and Development With Ada, Brooks Cole, ISBN 0314028293
  • Ian C. Pyle: Developing Safety Systems: A Guide Using Ada, Prentice Hall, ISBN 0132042983
  • Louis Baker: Artificial Intelligence With Ada, McGraw-Hill, ISBN 0070033501
  • Alan Burns, Andy Wellings: HRT-HOOD: A Structured Design Method for Hard Real-Time Ada Systems, North-Holland, ISBN 0444821643
  • Walter Savitch, Charles Peterson: Ada: An Introduction to the Art and Science of Programming, Benjamin-Cummings Publishing Company, ISBN 0805370706
  • Mark Allen Weiss: Data Structures and Algorithm Analysis in Ada, Benjamin-Cummings Publishing Company, ISBN 0805390553

Ada Wikis

General Info

Tutorials

Projects

External links

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