Ada (programming language)

Ada (programming Language)

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Ada (programming language)

Ada is a structured

Structured programming

Structured programming can be seen as a subset or subdiscipline of procedural programming, one of the major programming paradigms. It is most famous for removing or reducing reliance on the GOTO Statement ....
, statically typed, imperative

Imperative programming

In computer science, imperative programming is a programming paradigm that describes computation in terms of statement s that change a program state ....
, and object-oriented

Object-oriented programming

Object-oriented programming is a programming paradigm that uses "Object_" and their interactions to design applications and computer programs....
high-level computer

Computer programming

Computer programming is the process of writing, testing, debugging/troubleshooting, and maintaining the source code of computer programs. This source code is written in a programming language....
programming language

Programming language

A programming language is a machine-readable artificial language designed to express computations that can be performed by a machine, particularly a computer....
, extended from Pascal

Pascal (programming language)

Pascal is an influential imperative programming and Procedural programming programming language, designed in 1968/9 and published in 1970 by Niklaus Wirth as a small and efficient language intended to encourage good programming practices using structured programming and data structure....
and other languages. It was originally designed by a team led by Jean Ichbiah

Jean Ichbiah

Jean David Ichbiah was a France-born computer scientist and the chief designer of Ada programming language, a general-purpose, strongly-typed programming language with certified validated compilers....
of CII Honeywell Bull

Groupe Bull

Groupe Bull is a France owned computer company headquartered in Les Clayes-sous-Bois, outside Paris. The company has also been known at various times as Bull General Electric, Honeywell Bull, CII Honeywell Bull, and Bull HN....
under contract to the United States Department of Defense

United States Department of Defense

The United States Department of Defense is the federal department charged with coordinating and supervising all agencies and functions of the government relating directly to national security and the Military of the United States....
(DoD) from 1977 to 1983 to supersede the hundreds of programming languages then used by the DoD. Ada is strongly typed and compilers are validated for reliability in mission-critical applications, such as avionics

Avionics

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Features

Ada was originally targeted at embedded

Embedded system

An embedded system is a special-purpose computer system designed to perform one or a few dedicated functions, often with real-time computing constraints....
and real-time

Real-time computing

In computer science, real-time computing is the study of Computer hardware and computer software systems that are subject to a "real-time constraint"?i.e., operational deadlines from event to system response....
systems. The Ada 95 revision, designed by S. Tucker Taft of Intermetrics

Intermetrics

Intermetrics, Inc. was a software company founded in Cambridge, Massachusetts, Massachusetts in 1969 by several veterans of Massachusetts Institute of Technology Charles Stark Draper Laboratory who had worked on the software for NASA's Project Apollo including the Apollo Guidance Computer....
between 1992 and 1995, improved support for systems, numerical, financial, and object-oriented programming

Object-oriented programming

Object-oriented programming is a programming paradigm that uses "Object_" and their interactions to design applications and computer programs....
(OOP).

Notable features of Ada include: strong typing, modularity mechanisms

Modularity (programming)

Modular programming is a software design technique that increases the extent to which software is composed from separate parts, called modules. Conceptually, modules represent a separation of concerns, and improve maintainability by enforcing logical boundaries between components....
(packages), run-time checking

Run-time checking

Runtime checking is a mechanism of a programming language to check for errors at runtime, e.g. arithmetic overflows or invalid Cast . Most times an exception handling is thrown and/or the program is terminated, instead of ignoring this failure as it is done in C , C++ etc....
, parallel processing

Parallel processing

Parallel processing is the ability of an entity to carry out multiple operations or tasks simultaneously. The term is used in the contexts of both human cognition and machine computation....
(tasks), exception handling

Exception handling

Exception handling is a programming language construct or computer hardware mechanism designed to handle the occurrence of exceptions - special conditions that change the normal flow of execution....
, and generic

Generic programming

Generic programming is a style of computer programming in which algorithms are written in terms of to-be-specified-later types that are then instantiated when needed for specific types provided as parameters and was pioneered by Ada which appeared in 1983....
s. Ada 95 added support for object-oriented programming

Object-oriented programming

Object-oriented programming is a programming paradigm that uses "Object_" and their interactions to design applications and computer programs....
, including dynamic dispatch

Dynamic dispatch

In computer science, dynamic dispatch is the process of mapping a Message passing to a specific sequence of code at runtime. This is done to support the cases where the appropriate method cannot be determined at compile-time ....
.

Ada supports run-time checks in order to protect against access to unallocated memory, buffer overflow

Buffer overflow

In computer security and computer programming, a buffer overflow, or buffer overrun, is an Anomaly in software condition where a process attempts to store data beyond the boundaries of a fixed-length buffer ....
errors, off-by-one error

Off-by-one error

An off-by-one error is a logical error involving the discrete equivalent of a boundary condition. It often occurs in computer programming when an control flow#Loops iterates one time too many or too few....
s, array access errors, and other detectable bugs. These checks can be disabled in the interest of runtime 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

Anomaly in software

In software testing an anomaly is anything that differs from expectation. This expectation can result from many things like from a document or from a person's view or experiences ....
might lead to very serious consequences, i.e., accidental death or injury. Examples of systems where Ada is used include avionics

Avionics

Avionics means "aviation electronics". It comprises Electronics systems for use on aircraft, artificial satellites and spacecraft, comprising communications, navigation and the display and management of multiple systems....
, weapon systems (including thermonuclear weapons), and spacecraft

Spacecraft

A spacecraft is a Craft or machine designed for spaceflight. On a sub-orbital spaceflight, a spacecraft enters outer space then returns to the Earth....
.

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 is designed to detect small problems in very large, massive software systems. For example, Ada detects each misspelled variable (due to the rule to declare each variable name), and Ada pinpoints unclosed if-statements, which require "END IF" rather than mismatching with any "END" token. Also, Ada can spot procedure calls with incorrect parameters, which is a common problem in large, complex software where most of the statements are procedure calls.

Ada's dynamic memory management

Memory management

Memory management is the act of managing computer memory. In its simpler forms, this involves providing ways to allocate portions of memory to programs at their request, and freeing it for reuse when no longer needed....
is high-level and type-explicit, requiring explicit instantiation of the Unchecked_Deallocation package to explicitly free allocated memory. The specification does not require any particular implementation. Though the semantics of the language allow automatic garbage collection

Garbage collection (computer science)

In computer science, garbage collection is a form of automatic memory management. The garbage collector, or just collector, attempts to reclaim garbage , or memory used by Object that will never be accessed or mutated again by the Application software....
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. "||"). Ada uses the basic mathematical symbols (i.e.: "+", "-", "*" and "/") for basic mathematical operations but avoids using other symbols. Code blocks are delimited by words such as "declare", "begin" and "end". Conditional statements are closed with "end if", avoiding a dangling else
Dangling else

The dangling else is a well-known problem in computer programming in which a seemingly well-defined grammar can become ambiguous. In many programming languages you can write code like this:...
that could pair with the wrong nested if-expression in other languages.

Ada was designed to use the English language standard for comments: the em-dash, as a double-dash ("--") to denote comment text. Comments stop at end of line, so there is no danger of unclosed comments accidentally eating whole sections of source code. Comments can be nested: prefixing each line (or column) with "--" will skip all that code, while being clearly denoted as a column of repeated "--" down the page. There is no limit to the nesting of comments, thereby allowing prior code, with commented-out sections, to be commented-out as even larger sections. All characters are allowed in comments, such as for symbolic formulas (E[0]=m*c^2). To the compiler, the double-dash is treated as end-of-line, allowing continued parsing of the language as a context-free grammar

Context-free grammar

In formal language theory, a context-free grammar is a formal grammar in which every Production rule is of the formwhere V is a single nonterminal symbol, and w is a string of Terminal and nonterminal symbolss and/or nonterminals ....
.

The semicolon (";") is a statement terminator, so Ada avoids the very common problem where ";END" kills a Pascal

Pascal (programming language)

Compiler

A compiler is a computer program that transforms source code written in a programming language into another computer language . The most common reason for wanting to transform source code is to create an executable program....
because ";" is only a Pascal separator, never allowed either to terminate "END;" in Pascal.

Code for complex systems is typically maintained for many years, by programmers other than the original author. It can be argued that these language design principles apply to most software projects, and most phases of software development, but when applied to complex, safety critical projects, benefits in correctness, reliability, and maintainability take precedence over (arguable) costs in initial development.

Unlike most ISO

International Organization for Standardization

The International Organization for Standardization , widely known as ISO , is an international standard-setting body composed of representatives from various national standards organizations....
standards, the Ada language definition (known as the Ada Reference Manual or ARM, or sometimes the Language Reference Manual or LRM) is free content

Free content

Free content, or free information, is any kind of functional work, Work of art, or other creative Content having no significant legal restriction relative to people's freedom to use, redistribute, and produce modified versions of and works derived from the 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.

One notable Free Software tool that is used by many Ada programmers to aid them in writing Ada source code is GPS, the GNAT Programming Studio

GNAT Programming Studio

GNAT Programming Studio is a free software multi-language integrated development environment by AdaCore. GPS uses compilers from the GNU Compiler Collection, taking its name from GNAT, the GNU compiler for the Ada programming language....
.

History

In the 1970s, the US Department of Defense

United States Department of Defense

The United States Department of Defense is the federal department charged with coordinating and supervising all agencies and functions of the government relating directly to national security and the Military of the United States....
(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 High Order Language Working Group

High Order Language Working Group

The High Order Language Working Group was a working group instrumental in developing the Ada computer Computer programming Programming language....
(HOLWG) was formed with the intent to reduce 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

Working Group

Working Group can mean:*Working group, an interdisciplinary group of researchers; or*Working Group , kennel club designation for certain purebred dog breeds; or...
created a series of language requirements documents—the Strawman, Woodenman, Tinman, Ironman and Steelman

Steelman language requirements

The Steelman language requirements were a set of requirements which a high-level general-purpose programming language should meet, created by the United States Department of Defense in The Department of Defense Common High Order Language program in 1978....
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

Intermetrics

Intermetrics, Inc. was a software company founded in Cambridge, Massachusetts, Massachusetts in 1969 by several veterans of Massachusetts Institute of Technology Charles Stark Draper Laboratory who had worked on the software for NASA's Project Apollo including the Apollo Guidance Computer....
led by Benjamin Brosgol), Green (CII Honeywell Bull, led by Jean Ichbiah

Jean Ichbiah

SRI International

SRI International, founded as Stanford Research Institute, is one of the world's largest contract research institutes. Based in the United States, the trustees of Stanford University established it in 1946 as a center of innovation to support economic development in the region....
, led by Jay Spitzen). In April 1978, after public scrutiny, the Red and Green proposals passed to the next phase. In May 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

Ada Lovelace

Augusta Ada King, Countess of Lovelace , born Augusta Ada Byron, was the only legitimate child of George Gordon Byron, 6th Baron Byron. She is widely known in modern times simply as Ada Lovelace....
's birthday), and given the number MIL-STD-1815 in honor of Ada Lovelace's birth year. In 1981, C. A. R. Hoare

C. A. R. Hoare

Sir Charles Antony Richard Hoare , commonly known as Tony Hoare or C.A.R. Hoare, is a United Kingdom computer science, probably best known for the development in 1960 of Quicksort , one of the world's most widely used sorting algorithms....
took advantage of his Turing Award

Turing Award

The A. M. Turing Award is given annually by the Association for Computing Machinery to "an individual selected for contributions of a technical nature made to the computing community....
speech to criticize Ada for being overly complex and hence unreliable.

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

Commercial off-the-shelf

Commercial, off-the-shelf is a term for Computer software or hardware, generally technology or computer products, that are ready-made and available for sale, lease, or license to the general public....
) technology. Similar requirements existed in other NATO countries.

Because Ada is a strongly typed language, it has been used outside the military in commercial aviation projects, where a software bug can cause fatalities. The fly-by-wire

Aircraft flight control systems

Aircraft flight control systems consist of flight control surfaces, the respective cockpit controls, connecting linkages, and the necessary operating mechanisms to control an aircraft's direction in flight....
system software in the Boeing 777

Boeing 777

The Boeing 777 is a long-range, Wide-body aircraft twin-engine airliner manufactured by Boeing Commercial Airplanes. The world's largest twinjet and commonly referred to as the "Triple Seven", the aircraft can carry between 283 and 368 passengers in a three-class configuration, and has a range from 5,235 to 9,380 nautical miles ....
was written in Ada. The Canadian Automated Air Traffic System (completed in year 2000 by ) was written in 1 million lines of Ada (SLOC

Source lines of code

Source lines of code is a software metric used to measure the size of a Computer software by counting the number of lines in the text of the program's source code....
count). It featured advanced (for the time) distributed processing, a distributed Ada database, and object-oriented design.

Standardization

The language became an ANSI

American National Standards Institute

The American National Standards Institute or ANSI is a private non-profit organization that oversees the development of voluntary consensus standards for products, services, processes, systems, and personnel in the United States....
standard in 1983 (), and without any further changes became an ISO standard

International standard

International standards are standards developed by international standards organisations. International standards are available for consideration and use, worldwide....
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 () 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

Gnat

Gnat is a colloquial name for many small insects in the order Diptera and specifically within the suborder Nematocera.The males often assemble together in large mating swarms, particularly at dusk, called a "ghost"....
Compiler

Compiler

GNU Compiler Collection

The GNU Compiler Collection is a compiler system produced by the GNU Project supporting various programming languages. GCC is a key component of the GNU toolchain....
.

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, and a major Amendment, , was published on March 9, 2007. Other related standards include ISO 8651-3:1988 Information processing systems -- Computer graphics -- Graphical Kernel System (GKS) language bindings -- Part 3: Ada

"Hello, world!" in Ada

A common example of a language's syntax

Syntax

In linguistics, syntax is the study of the principles and rules for constructing Sentence s in natural languages. In addition to referring to the discipline, the term syntax is also used to refer directly to the rules and principles that govern the sentence structure of any individual language, as in "the Irish syntax"....
is the Hello world program

Hello world program

A "Hello World" program is a computer program that prints out "Hello world!" on a display device. It is used in many introductory tutorials for teaching a programming language....
: with Ada.Text_IO;

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

Ada also provides alternative constructions that are more streamlined.

Ada (programming language)

Features

History

Standardization

"Hello, world!" in Ada

See also

International Standards

Rationale

Books

Archives

External links