Ada programming language

Ada is a structured, compiled, statically typed programming language, designed by Jean Ichbiah[?] of Honnywell Bull[?] in the 1970s. It is positioned to address much the same tasks as C or C++. Ada was named after Lady Ada Lovelace, the so-called first computer programmer.

Language Features

Ada was originally targetted 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 generics. Ada 95 added support for object-oriented programming, including dynamic dispatch.

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.

One very expensive European Space Agency Ariane 5 rocket was lost due to arithmetic overflow in an Ada program, in which the relevant check was disabled.

The Ada language definition is unusual among International Organization for Standardization standards in that it is Free content. One effect of this is that the standard document (known as the Reference Manual or RM) is the usual reference resorted to by Ada programmers for technical details, much as many other languages have a standard textbook.

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, Green, Blue, and Yellow. In May of 1979, the Green proposal, designed by Jean Ichbiah at Cii Honeywell Bull, was chosen and given the name Ada. The 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), 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.

Compiler problems

Early versions of compilers written to the Ada 80 specification were rushed to market and were poorly optimized; resulting in slow compilations, and generated code that both ran slow and consumed excessive amounts of memory. With the captive market created by the Ada mandate, compiler vendors had little motivation to correct these problems.

The Ada 80 specification also contained rules for "Elaboration" derived from Multics that were inefficient to implement without special hardware features that most computers that Ada would run on lacked.

The Ada 83 specification contained many corrections for and improvements that made compiler writing easier and the compiler vendors now had the experience with the language needed to produce high quality compiler products. However for many of the early users these improvements were considered to be too late and significant resistance to usage of the language developed among them.

Modern compilers written to the Ada 95 specification are stable highly optimized compilers, having none of the problems of the early ones.