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Ada programming language
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Ada programming language

Ada is a structured, statically typed programming language, designed by Jean Ichbiah of Cii Honeywell Bull in the 1970s. It is positioned to address much the same tasks as C or C++. Ada was named after Ada, Lady Lovelace, the first computer programmer.

Table of contents
1 Language Features
2 History
3 "Hello, World!" in Ada
4 The Ariane 5 Failure
5 See also
6 References
7 External links

Language 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 Tucker Taft of Intermetrics between 1992 and 1995) improved support for systems, numerical, and financial programming.

Notable features of Ada include Strong typing, run-time checking, parallel processing, exception handling, and genericss. Ada 95 added support for object-oriented programming, including dynamic dispatch and C++ like templates.

Ada implementations do not typically use garbage collection for storage management. Ada supports a limited form of region-based storage management, which allows some cases of access to unallocated memory to be detected at compile time.

Ada supports run-time checks in order to protect against access to unallocated memory, buffer overflow errors, off by one errors, and other avoidable bugs. These checks can be disabled in the interest of efficiency. 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.

The Ada language definition is unusual among International Organization for Standardization standards in that it is Free content. One result of this is that the standard document (known as the Reference Manual or RM) 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 was concerned by the number of different programming languages being used for its projects, some of which were proprietary and/or obsolete. 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.

The working group created a series of language requirements documents - the Strawman, Tinman, and Ironman (and later 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), Green (Cii Honeywell Bull), Blue (SofTEch), and Yellow (SRI International). In May of 1979, the Green proposal, designed by Jean Ichbiah at Cii Honeywell Bull, was chosen and given the name Ada. This proposal was a successor to the programming language LIS that Ichbiah and his group had developed in the 1970's.

The Military Standard reference manual was approved on December 10, 1980 (Ada Lovelace's birthday).

The US Department of Defense required the use 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. Similar requirements existed in other North Atlantic Treaty Organization countries.

The language became an ANSI standard in 1983 (ANSI/MIL-STD 1815 (1815 is Ada Lovelace's birthyear)), and 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.

Ada 95, the joint ISO/ANSI standard (ISO-8652:1995) is the latest standard for Ada. It was accepted 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.

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 an Addendum to Ada 95 expected in 2005.

"Hello, World!" in Ada

A common example of a language's syntax is the Hello world program.
with Ada.Text_Io; 
use Ada.Text_Io;
procedure Hello is
begin
   Put_Line("Hello World!");
end Hello;

The Ariane 5 Failure

A commonly encountered myth blames the loss of a
European Space Agency Ariane 5 rocket on a bug in an Ada program or on disabling Ada's runtime checks. Though 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 Ariane 5 Flight 501.

See also

References

External links



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