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Ada (programming language)

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Ada
File:Ada-cover.jpg
Paradigmmulti-paradigm: concurrent, distributed, generic-programming, imperative, object-oriented
Designed byJean Ichbiah
First appeared1983, last revised 2005
Typing disciplinestatic, strong, safe, nominative
Websiteadaic.org
Major implementations
GNAT
Dialects
Ada 83, Ada 95, Ada 2005
Influenced by
ALGOL 68, Pascal, C++ (Ada 95), Smalltalk (Ada 95), Java (Ada 2005)
Influenced
C++, PL/SQL, Ruby, Python

Ada is a structured, statically typed imperative computer programming language designed by a team led by Jean Ichbiah of CII Honeywell Bull under contract to the United States Department of Defense during 1977–1983. It addresses many of the same tasks as C or C++, but with one of the most ridiculous type-safety systems available in a statically typed programming language. Ada was named after Ada Lovelace, who is often credited with being the first computer programmer [citation needed].

As a result, the DoD created a grossly overworded language which rarely serves a purpose and doesn't use modern programming techniques. Yet, defense companies love it because they get paid a slightly below average salary for doing the same job in 3x the amount of time without benefit. This is known as job security. Many companies have now instated a policy where any time a worker says, "I like Ada better than C++", that that programmer is instantly fired and possible executed.

Features

Ada was originally targeted at embedded and real-time systems. The Ada 95 revision, designed by S. Daffy Duck of Looney Toons 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. One of the nice things about Ada is how it takes six weeks just to get a "Hello World!" program to compile.

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 Ada is widely used in critical systems, where any anomaly will lead to very serious consequences ie accidental death or injury. Examples of systems where Ada is used include avionics, weapons (including thermonuclear weapons) and spacecraft.

Ada 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 syntax of Ada is simple, consistent and readable. It minimizes choices of ways to perform basic operations, and prefers English keywords (eg "OR") to symbols (eg. "||"). Thus it avoids terse constructs such as "||", "++", and "+=" (of the C language), and enforces that each conditional statement be closed. The rationale is that code for a complex system must be readable by reviewers and maintainers. Reviewers may include domain experts who are not highly software literate. Code for complex systems is typically maintained for many years, by programmers other than the original author. It can be argued that the language design benefits apply to most software projects, and most phases of software development, however when applied to complex, safety critical projects, benefits in correctness, reliability, and maintainability take precedence over (arguable) costs in initial development.

Unlike most ISO standards, the Ada language definition (known as the Ada Reference Manual or ARM, or sometimes the Language Reference Manual or LRM) is free content. Thus, it is a common reference for Ada programmers, not just programmers implementing Ada compilers. Apart from the reference manual, there is also an extensive rationale document which explains the language design and the use of various language constructs. This document is also widely used by programmers. When the language was revised, a new rationale document was written.

History

In the 1970s, the US Department of Defense (DoD) was concerned by the number of different programming languages being used for its embedded computer system 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.

Wikisource has original text related to this article:

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.

Augusta Ada King, Countess of Lovelace.

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 strongly-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 Canadian Automated Air Traffic System (completed in year 2000 by Raytheon Canada) was written in 1 million lines of Ada (SLOC count). It featured advanced (for the time): distributed processing; a distributed Ada database; and object oriented design.

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 referred to 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. Presently, the GNAT Compiler is part of the GNU Compiler Collection.

Work has continued on improving and updating the technical content of the Ada programming language. A Technical Corrigendum to Ada 95 was published in October 2001. Roughly once-a-decade Ada undergoes a major update. The latest version is Ada 2005. As of 2006, this version is already prompt in reference text and compilers, though the official ISO publication might lag behind a bit (see current status).


Thankfully, Ada is now dead. Except for in a few defense companies, which are clearly misguided and wrong.

"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.

Criticism

The Ariane 5 failure

The maiden flight loss of Ariane 5 Flight 501, a European Space Agency Ariane 5 launcher, was due to an error in a program written in Ada for checks of the launcher while on the ground. During the beginning of the flight a run-time error occurred that was not covered by an exception handler and therefore propagated to the main guidance program leading to main processor shut down and loss of guidance. Management of the Ariane 5 project had decided that since the same program worked well for all the flights of the Ariane 4 it would be reused directly, without being adapted, for the Ariane 5. However, the flight parameters of Ariane 5 were different and when one value failed a range check that was impossible to fail on an Ariane 4 there was no code in place to handle the resulting exception. The incident led to discussions on the use of Ada as a possible contributing factor, in particular concerning the design of Ada's run-time error handling.

See also

Online tutorials

The following sites have link collections to Ada tutorials:

Organizations

Compilers

  • AdaMagic - Proprietary Ada technology from SofCheck, including Ada 95 front end, run-time system, and tools; front end can generate conventional IL, ISO/ANSI C, or Java byte codes
  • GNAT - Free compiler based on GCC
  • GNATPro - Commercially supported version of GNAT from AdaCore
  • JGNAT - GNAT-based compiler for the Java Runtime Environment
  • MGNAT - GNAT-based compiler for the .NET Framework Environment (A# project)
  • ObjectAda - Proprietary Ada compiler from Aonix
  • PowerAda - Proprietary Ada Compiler from OC Systems
  • AdaMutli - Proprietary Ada Compiler and Integrated Development Environment from Greenhills
  • Score - Proprietary compiler suite from DDC-I that supports Ada as one of its languages
  • Rational Apex (now owned and sold by IBM)

Tools

  • SPARK - High integrity language based on an Ada subset
  • VHDL - A hardware description language for representing digital hardware, with many concepts and much syntax borrowed from Ada.
  • PL/SQL - Stored procedure language in Oracle Corporation's RDBMS product, has many similarities to Ada and was historically based on Ada syntax

See also

References

International Standards

Rationale

(These documents have been published in various forms including print.)

Books

The Wikibook [[wikibooks:|]] has a page on the topic of: Ada Programming
  • Jan Skansholm: Ada 95 From the Beginning, Addison-Wesley, ISBN 0-201-40376-5
  • John Barnes: Programming in Ada 2005, Addison-Wesley, ISBN 0-321-34078-7
  • 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 0-201-17517-7
  • John Barnes: High Integrity Software: The SPARK Approach to Safety and Security, Addison-Wesley, ISBN 0-321-13616-0
  • John Beidler: Data Structures and Algorithms: An Object-Oriented Approach Using Ada 95, Springer-Verlag, ISBN 0-387-94834-1
  • Dean W. Gonzalez: Ada Programmer's Handbook, Benjamin-Cummings Publishing Company, ISBN 0-8053-2529-8
  • 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 0-07-011607-5
  • 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 0-201-56527-7
  • Grady Booch, Doug Bryan: Software Engineering with Ada, Addison-Wesley, ISBN 0-8053-0608-0
  • 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 0-13-264680-3
  • John English, Fintan Culwin: Ada 95 the Craft of Object Oriented Programming, Prentice Hall, ISBN 0-13-230350-7
  • 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 0-387-97133-5
  • Michael B. Feldman: Software Construction and Data Structures with Ada 95, Addison-Wesley, ISBN 0-201-88795-9
  • Simon Johnston: Ada 95 for C and C++ Programmers, Addison-Wesley, ISBN 0-201-40363-3
  • 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 0-7637-0293-5
  • Nell Dale, John McCormick: Ada Plus Data Structures: An Object-Oriented Approach, 2nd edition, Jones & Bartlett Publishers, ISBN 0-7637-3794-1
  • Bruce C. Krell: Developing With Ada: Life-Cycle Methods, Bantam Dell Pub Group, ISBN 0-553-09102-6
  • 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 0-13-030834-X
  • Bruce Hillam: Introduction to Abstract Data Types Using Ada, Prentice Hall, ISBN 0-13-045949-6
  • David Rudd: Introduction to Software Design and Development With Ada, Brooks Cole, ISBN 0-314-02829-3
  • Ian C. Pyle: Developing Safety Systems: A Guide Using Ada, Prentice Hall, ISBN 0-13-204298-3
  • Louis Baker: Artificial Intelligence With Ada, McGraw-Hill, ISBN 0-07-003350-1
  • Alan Burns, Andy Wellings: HRT-HOOD: A Structured Design Method for Hard Real-Time Ada Systems, North-Holland, ISBN 0-444-82164-3
  • Walter Savitch, Charles Peterson: Ada: An Introduction to the Art and Science of Programming, Benjamin-Cummings Publishing Company, ISBN 0-8053-7070-6
  • Mark Allen Weiss: Data Structures and Algorithm Analysis in Ada, Benjamin-Cummings Publishing Company, ISBN 0-8053-9055-3
  • Henry Ledgard: ADA: AN INTRODUCTION (Second Edition), Springer-Verlag, ISBN 0-387-90814-5

GNAT - Free Ada compiler

Ada Wikis

General Info

Tutorials

Projects

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