AdaCore GNAT,[2] Green Hills Software Optimising Ada 95 compiler, PTC ApexAda and ObjectAda,[3] MapuSoft Ada-C/C++ changer,[4] formerly known as "AdaMagic with C Intermediate",[5] DDC-I Score
Ada was originally designed for embedded and real-time systems. The Ada95 revision, designed by S. Tucker Taft of Intermetrics between 1992 and 1995, improved support for systems, numerical, financial, and object-oriented programming (OOP).
The syntax of Ada minimizes choices of ways to perform basic operations, and prefers English keywords (such as "or else" and "and then") to symbols (such as "||" and "&&"). Ada uses the basic arithmetical operators "+", "-", "*", and "/", but avoids using other symbols. Code blocks are delimited by words such as "declare", "begin", and "end", where the "end" (in most cases) is followed by the identifier of the block it closes (e.g., if ... end if, loop ... end loop). In the case of conditional blocks this avoids a dangling else that could pair with the wrong nested if-expression in other languages like C or Java.
Ada is designed for developing very large software systems. Ada packages can be compiled separately. Ada package specifications (the package interface) can also be compiled separately without the implementation to check for consistency. This makes it possible to detect problems early during the design phase, before implementation starts.
A large number of compile-time checks are supported 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. For example, the syntax requires explicitly named closing of blocks to prevent errors due to mismatched end tokens. The adherence to strong typing allows detecting many common software errors (wrong parameters, range violations, invalid references, mismatched types, etc.) either during compile-time, or otherwise during run-time. As concurrency is part of the language specification, the compiler can in some cases detect potential deadlocks.[14] Compilers also commonly check for misspelled identifiers, visibility of packages, redundant declarations, etc. and can provide warnings and useful suggestions on how to fix the error.
Ada also supports run-time checks to protect against access to unallocated memory, buffer overflow errors, range violations, off-by-one errors, 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 sometimes used in critical systems, where any anomaly might lead to very serious consequences, e.g., accidental death, injury or severe financial loss. Examples of systems where Ada is used include avionics, air traffic control, railways, banking, military and space technology.[15][16]
Ada's dynamic memory management is high-level and type-safe. Ada has no generic or untyped pointers; nor does it implicitly declare any pointer type. Instead, all dynamic memory allocation and deallocation must occur via explicitly declared access types. Each access type has an associated storage pool that handles the low-level details of memory management; the programmer can either use the default storage pool or define new ones (this is particularly relevant for Non-Uniform Memory Access). It is even possible to declare several different access types that all designate the same type but use different storage pools. Also, the language provides for accessibility checks, both at compile time and at run time, that ensures that an access value cannot outlive the type of the object it points to.[17]
Though the semantics of the language allow automatic garbage collection of inaccessible objects, most implementations do not support it by default, as it would cause unpredictable behaviour in real-time systems. Ada does support a limited form of region-based memory management; also, creative use of storage pools can provide for a limited form of automatic garbage collection, since destroying a storage pool also destroys all the objects in the pool.
A double-dash ("--"), resembling an em dash, denotes comment text. Comments stop at end of line; there is intentionally no way to make a comment span multiple lines, to prevent unclosed comments from accidentally voiding whole sections of source code. Disabling a whole block of code therefore requires the prefixing of each line (or column) individually with "--". While this clearly denotes disabled code by creating a column of repeated "--" down the page, it also renders the experimental dis/re-enablement of large blocks a more drawn-out process in editors without block commenting support.
The semicolon (";") is a statement terminator, and the null or no-operation statement is null;. A single ; without a statement to terminate is not allowed.
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 only 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 the GNAT Programming Studio, and GNAT which is part of the GNU Compiler Collection.
History
In the 1970s the US Department of Defense (DoD) became 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, a working group, the High Order Language Working Group (HOLWG), was formed with the intent to reduce this number by finding or creating a programming language generally suitable for the department's and the UK Ministry of Defence's requirements. After many iterations beginning with an original straw-man proposal[18] the eventual programming language was named Ada. The total number of high-level programming languages in use for such projects fell from over 450 in 1983 to 37 by 1996.
HOLWG crafted the Steelman language requirements, a series of documents stating the requirements they felt a programming language should satisfy. Many existing languages were formally reviewed, but the team concluded in 1977 that no existing language met the specifications.
Watercolour painting of Ada Lovelace
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 (Honeywell, led by Jean Ichbiah), Blue (SofTech, led by John Goodenough)[19] 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 1979, the Green proposal, designed by Jean Ichbiah at Honeywell, was chosen and given the name Ada—after Augusta Ada King, Countess of Lovelace, usually known as Ada Lovelace. This proposal was influenced by the 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 1981, Tony Hoare took advantage of his Turing Award speech to criticize Ada for being overly complex and hence unreliable,[20] but subsequently seemed to recant in the foreword he wrote for an Ada textbook.[21]
Ada attracted much attention from the programming community as a whole during its early days. Its backers and others predicted that it might become a dominant language for general purpose programming and not only defense-related work.[22] Ichbiah publicly stated that within ten years, only two programming languages would remain: Ada and Lisp.[23] Early Ada compilers struggled to implement the large, complex language, and both compile-time and run-time performance tended to be slow and tools primitive.[22] Compiler vendors expended most of their efforts in passing the massive, language-conformance-testing, government-required Ada Compiler Validation Capability (ACVC) validation suite that was required in another novel feature of the Ada language effort.[23]
In 1991, the US Department of Defense began to require the use of Ada (the Ada mandate) for all software,[27] though exceptions to this rule were often granted.[22] The Department of Defense Ada mandate was effectively removed in 1997, as the DoD began to embrace commercial off-the-shelf (COTS) technology.[22] Similar requirements existed in other NATO countries: Ada was required for NATO systems involving command and control and other functions, and Ada was the mandated or preferred language for defense-related applications in countries such as Sweden, Germany, and Canada.[28]
By the late 1980s and early 1990s, Ada compilers had improved in performance, but there were still barriers to fully exploiting Ada's abilities, including a tasking model that was different from what most real-time programmers were used to.[23]
Because of Ada's safety-critical support features, it is now used not only for military applications, but also in commercial projects where a software bug can have severe consequences, e.g., avionics and air traffic control, commercial rockets such as the Ariane 4 and 5, satellites and other space systems, railway transport and banking.[16] For example, the Primary Flight Control System, the fly-by-wire system software in the Boeing 777, was written in Ada, as were the fly-by-wire systems for the aerodynamically unstable Eurofighter Typhoon,[29]Saab Gripen,[30]Lockheed Martin F-22 Raptor and the DFCS replacement flight control system for the Grumman F-14 Tomcat. The Canadian Automated Air Traffic System was written in 1 million lines of Ada (SLOC count). It featured advanced distributed processing, a distributed Ada database, and object-oriented design. Ada is also used in other air traffic systems, e.g., the UK's next-generation Interim Future Area Control Tools Support (iFACTS) air traffic control system is designed and implemented using SPARK Ada.[31] It is also used in the FrenchTVM in-cab signalling system on the TGV high-speed rail system, and the metro suburban trains in Paris, London, Hong Kong and New York City.[16][32]
Standardization
Timeline of Ada language
Year
Informal name
ANSI Standard
ISO/IEC Standard
1980
Ada
MIL-STD 1815
—
1983
Ada 83/87
MIL-STD 1815A
8652:1987
1995
Ada 95
—
8652:1995
2007
Ada 2005
—
8652:1995/Amd 1:2007
2012
Ada 2012
—
8652:2012
2023
Ada 2022
—
8652:2023
Preliminary Ada can be found in ACM Sigplan Notices Vol 14, No 6, June 1979[33]
Ada was first published in 1980 as an ANSI standard ANSI/MIL-STD 1815. As this very first version held many errors and inconsistencies ,[a] the revised edition was published in 1983 as ANSI/MIL-STD 1815A. Without any further changes, it became an ISO standard in 1987.[35] This version of the language is commonly known as Ada83, from the date of its adoption by ANSI, but is sometimes referred to also as Ada87, from the date of its adoption by ISO.[36] There is also a French translation; DIN translated it into German as DIN 66268 in 1988.
Ada95, the joint ISO/IEC/ANSI standard ISO/IEC 8652:1995[37][38] was published in February 1995, making it 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 GNATCompiler. Presently, the GNAT Compiler is part of the GNU Compiler Collection.
Work has continued on improving and updating the technical content of the Ada language. A Technical Corrigendum to Ada95 was published in October 2001,[39][40] and a major Amendment, ISO/IEC 8652:1995/Amd 1:2007 [41][42] was published on March 9, 2007, commonly known as Ada2005 because work on the new standard was finished that year.
At the Ada-Europe 2012 conference in Stockholm, the Ada Resource Association (ARA) and Ada-Europe announced the completion of the design of the latest version of the Ada language and the submission of the reference manual to the ISO/IEC JTC 1/SC 22/WG 9 of the International Organization for Standardization (ISO) and the International Electrotechnical Commission (IEC) for approval. ISO/IEC 8652:2012[43](see Ada 2012 RM) was published in December 2012, known as Ada2012. A technical corrigendum, ISO/IEC 8652:2012/COR 1:2016, was published [44](see RM 2012 with TC 1).
On May 2, 2023, the Ada community saw the formal approval of publication of the Ada2022 edition of the programming language standard.[11]
Despite the names Ada 83, 95 etc., legally there is only one Ada standard, the one of the last ISO/IEC standard: with the acceptance of a new standard version, the previous one becomes withdrawn. The other names are just informal ones referencing a certain edition.
Other related standards include ISO/IEC 8651-3:1988 Information processing systems—Computer graphics—Graphical Kernel System (GKS) language bindings—Part 3: Ada.
Language constructs
Ada is an ALGOL-like programming language featuring control structures with reserved words such as if, then, else, while, for, and so on. However, Ada also has many data structuring facilities and other abstractions which were not included in the original ALGOL 60, such as type definitions, records, pointers, enumerations. Such constructs were in part inherited from or inspired by Pascal.
This program can be compiled by using the freely available open source compiler GNAT, by executing
gnatmakehello.adb
Data types
Ada's type system is not based on a set of predefined primitive types but allows users to declare their own types. This declaration in turn is not based on the internal representation of the type but on describing the goal which should be achieved. This allows the compiler to determine a suitable memory size for the type, and to check for violations of the type definition at compile time and run time (i.e., range violations, buffer overruns, type consistency, etc.). Ada supports numerical types defined by a range, modulo types, aggregate types (records and arrays), and enumeration types. Access types define a reference to an instance of a specified type; untyped pointers are not permitted. Special types provided by the language are task types and protected types.
subtypeWorking_HoursisHoursrange0..12;-- at most 12 Hours to work a daysubtypeWorking_DayisWeekdayrangeMonday..Friday;-- Days to workWork_Load:constantarray(Working_Day)ofWorking_Hours-- implicit type declaration:=(Friday=>6,Monday=>4,others=>10);-- lookup table for working hours with initialization
Types can have modifiers such as limited, abstract, private etc. Private types do not show their inner structure; objects of limited types cannot be copied.[45] Ada 95 adds further features for object-oriented extension of types.
Control structures
Ada is a structured programming language, meaning that the flow of control is structured into standard statements. All standard constructs and deep-level early exit are supported, so the use of the also supported "go to" commands is seldom needed.
-- while a is not equal to b, loop.whilea/=bloopAda.Text_IO.Put_Line("Waiting");endloop;ifa>bthenAda.Text_IO.Put_Line("Condition met");elseAda.Text_IO.Put_Line("Condition not met");endif;foriin1..10loopAda.Text_IO.Put("Iteration: ");Ada.Text_IO.Put(i);Ada.Text_IO.Put_Line;endloop;loopa:=a+1;exitwhena=10;endloop;caseiiswhen0=>Ada.Text_IO.Put("zero");when1=>Ada.Text_IO.Put("one");when2=>Ada.Text_IO.Put("two");-- case statements have to cover all possible cases:whenothers=>Ada.Text_IO.Put("none of the above");endcase;foraWeekdayinWeekday'Rangeloop-- loop over an enumerationPut_Line(Weekday'Image(aWeekday));-- output string representation of an enumerationifaWeekdayinWorking_Daythen-- check of a subtype of an enumerationPut_Line(" to work for "&Working_Hours'Image(Work_Load(aWeekday)));-- access into a lookup tableendif;endloop;
Packages, procedures and functions
Among the parts of an Ada program are packages, procedures and functions.
Functions differ from procedures in that they must return a value. Function calls cannot be used "as a statement", and their result must be assigned to a variable. However, since Ada 2012, functions are not required to be pure and may mutate their suitably declared parameters or the global state.[46]
withAda.Text_IO;packagebodyExampleisi:Number:=Number'First;procedurePrint_and_Increment(j: inoutNumber)isfunctionNext(k: inNumber)returnNumberisbeginreturnk+1;endNext;beginAda.Text_IO.Put_Line("The total is: "&Number'Image(j));j:=Next(j);endPrint_and_Increment;-- package initialization executed when the package is elaboratedbeginwhilei<Number'LastloopPrint_and_Increment(i);endloop;endExample;
This program can be compiled, e.g., by using the freely available open-source compiler GNAT, by executing
gnatmake-zexample.adb
Packages, procedures and functions can nest to any depth, and each can also be the logical outermost block.
Each package, procedure or function can have its own declarations of constants, types, variables, and other procedures, functions and packages, which can be declared in any order.
Pragmas
A pragma is a compiler directive that conveys information to the compiler to allow specific manipulating of compiled output.[47] Certain pragmas are built into the language,[48] while others are implementation-specific.
Examples of common usage of compiler pragmas would be to disable certain features, such as run-time type checking or array subscript boundary checking, or to instruct the compiler to insert object code instead of a function call (as C/C++ does with inline functions).
Ada has had generics since it was first designed in 1977–1980. The standard library uses generics to provide many services. Ada 2005 adds a comprehensive generic container library to the standard library, which was inspired by C++'s standard template library.
A generic unit is a package or a subprogram that takes one or more generic formal parameters.[49]
A generic formal parameter is a value, a variable, a constant, a type, a subprogram, or even an instance of another, designated, generic unit. For generic formal types, the syntax distinguishes between discrete, floating-point, fixed-point, access (pointer) types, etc. Some formal parameters can have default values.
To instantiate a generic unit, the programmer passes actual parameters for each formal. The generic instance then behaves just like any other unit. It is possible to instantiate generic units at run-time, for example inside a loop.
APSE – a specification for a programming environment to support software development in Ada
Ravenscar profile – a subset of the Ada tasking features designed for safety-critical hard real-time computing
SPARK – a programming language consisting of a highly restricted subset of Ada, annotated with meta-information describing desired component behavior and individual runtime requirements
↑ Fuegi, J; Francis, J (2003). "Lovelace & Babbage and the creation of the 1843 'notes'". IEEE Annals of the History of Computing. 25 (4): 16–26. doi:10.1109/MAHC.2003.1253887. S2CID40077111.
↑ Dewar, Robert B. K.; Fisher, Gerald A. Jr.; Schonberg, Edmond; Froelich, Robert; Bryant, Stephen; Goss, Clinton F.; Burke, Michael (November 1980). "The NYU Ada translator and interpreter". Proceeding of the ACM-SIGPLAN symposium on Ada programming language – SIGPLAN '80. Vol.15. pp.194–201. doi:10.1145/948632.948659. ISBN0-89791-030-3. S2CID10586359.
1 2 "Ada Validated Compilers List". Ada Information Clearinghouse. July 1, 1992. pp.1–36.
A computer program is a sequence or set of instructions in a programming language for a computer to execute. It is one component of software, which also includes documentation and other intangible components.
C is a general-purpose programming language. It was created in the 1970s by Dennis Ritchie and remains very widely used and influential. By design, C's features cleanly reflect the capabilities of the targeted CPUs. It has found lasting use in operating systems code, device drivers, and protocol stacks, but its use in application software has been decreasing. C is commonly used on computer architectures that range from the largest supercomputers to the smallest microcontrollers and embedded systems.
Common Lisp (CL) is a dialect of the Lisp programming language, published in American National Standards Institute (ANSI) standard document ANSI INCITS 226-1994 (S2018). The Common Lisp HyperSpec, a hyperlinked HTML version, has been derived from the ANSI Common Lisp standard.
Fortran is a third generation, compiled, imperative programming language that is especially suited to numeric computation and scientific computing.
Java is a high-level, class-based, object-oriented programming language that is designed to have as few implementation dependencies as possible. It is a general-purpose programming language intended to let programmers write once, run anywhere (WORA), meaning that compiled Java code can run on all platforms that support Java without the need to recompile. Java applications are typically compiled to bytecode that can run on any Java virtual machine (JVM) regardless of the underlying computer architecture. The syntax of Java is similar to C and C++, but has fewer low-level facilities than either of them. The Java runtime provides dynamic capabilities that are typically not available in traditional compiled languages.
The unified modeling language (UML) is a general-purpose visual modeling language that is intended to provide a standard way to visualize the design of a system.
C++ is a high-level, general-purpose programming language created by Danish computer scientist Bjarne Stroustrup. First released in 1985 as an extension of the C programming language, it has since expanded significantly over time; as of 1997, C++ has object-oriented, generic, and functional features, in addition to facilities for low-level memory manipulation for systems like microcomputers or to make operating systems like Linux or Windows. It is usually implemented as a compiled language, and many vendors provide C++ compilers, including the Free Software Foundation, LLVM, Microsoft, Intel, Embarcadero, Oracle, and IBM.
Generic programming is a style of computer programming in which algorithms are written in terms of data types to-be-specified-later that are then instantiated when needed for specific types provided as parameters. This approach, pioneered by the ML programming language in 1973, permits writing common functions or types that differ only in the set of types on which they operate when used, thus reducing duplicate code.
The Standard Template Library (STL) is a software library originally designed by Alexander Stepanov for the C++ programming language that influenced many parts of the C++ Standard Library. It provides four components called algorithms, containers, functions, and iterators.
In computer science, imperative programming is a programming paradigm of software that uses statements that change a program's state. In much the same way that the imperative mood in natural languages expresses commands, an imperative program consists of commands for the computer to perform. Imperative programming focuses on describing how a program operates step by step, rather than on high-level descriptions of its expected results.
Programming languages can be grouped by the number and types of paradigms supported.
In computer science, a lock or mutex is a synchronization primitive that prevents state from being modified or accessed by multiple threads of execution at once. Locks enforce mutual exclusion concurrency control policies, and with a variety of possible methods there exist multiple unique implementations for different applications.
The following outline is provided as an overview of and topical guide to software engineering:
In computing, a null pointer or null reference is a value saved for indicating that the pointer or reference does not refer to a valid object. Programs routinely use null pointers to represent conditions such as the end of a list of unknown length or the failure to perform some action; this use of null pointers can be compared to nullable types and to the Nothing value in an option type.
The Ada Semantic Interface Specification (ASIS) is a layered, open architecture providing vendor-independent access to the Ada Library Environment. It allows for the static analysis of Ada programs and libraries. It is an open, published interface library that consists of the Ada environment and their tools and applications.
C# is a general-purpose high-level programming language supporting multiple paradigms. C# encompasses static typing, strong typing, lexically scoped, imperative, declarative, functional, generic, object-oriented (class-based), and component-oriented programming disciplines.
Programming languages are used for controlling the behavior of a machine. Like natural languages, programming languages follow rules for syntax and semantics.
assert.h is a header file in the C standard library. It defines the C preprocessor macro assert and implements runtime assertion in C.
In C++ computer programming, allocators are a component of the C++ Standard Library. The standard library provides several data structures, such as list and set, commonly referred to as containers. A common trait among these containers is their ability to change size during the execution of the program. To achieve this, some form of dynamic memory allocation is usually required. Allocators handle all the requests for allocation and deallocation of memory for a given container. The C++ Standard Library provides general-purpose allocators that are used by default, however, custom allocators may also be supplied by the programmer.
Modula-2 is a structured, procedural programming language developed between 1977 and 1985/8 by Niklaus Wirth at ETH Zurich. It was created as the language for the operating system and application software of the Lilith personal workstation. It was later used for programming outside the context of the Lilith.
References
International standards
ISO/IEC 8652: Information technology—Programming languages—Ada
ISO/IEC 15291: Information technology—Programming languages—Ada Semantic Interface Specification (ASIS)
ISO/IEC 18009: Information technology—Programming languages—Ada: Conformity assessment of a language processor (ACATS)
Dale, Nell B.; Weems, Chip; McCormick, John (August 1996). Programming and Problem Solving with Ada 95. Jones & Bartlett Publishers. ISBN0-7637-0293-5.
Dale, Nell B.; McCormick, John (2007). Ada Plus Data Structures: An Object-Oriented Approach, 2nd edition. Jones & Bartlett Publishers. ISBN978-0-7637-3794-8.
Krell, Bruce C. (1992). Developing With Ada: Life-Cycle Methods. Bantam Dell Pub Group. ISBN0-553-09102-6.
Bishop, Judy (10 May 1990). Distributed Ada: Developments and Experiences. Cambridge University Press. ISBN0-521-39251-9.
Sanden, Bo (1994). Software Systems Construction With Examples in Ada. Prentice Hall. ISBN0-13-030834-X.
Hillam, Bruce (1994). Introduction to Abstract Data Types Using Ada. Prentice Hall. ISBN0-13-045949-6.
Rudd, David (1994). Introduction to Software Design and Development With Ada. Brooks Cole. ISBN0-314-02829-3.
Pyle, Ian C. (1991). Developing Safety Systems: A Guide Using Ada. Prentice Hall. ISBN0-13-204298-3.
Baker, Louis (1989). Artificial Intelligence With Ada. McGraw-Hill. ISBN0-07-003350-1.
Savitch, Walter; Peterson, Charles (1992). Ada: An Introduction to the Art and Science of Programming. Benjamin-Cummings Publishing Company. ISBN0-8053-7070-6.
Weiss, Mark Allen (1993). Data Structures and Algorithm Analysis in Ada. Benjamin-Cummings Publishing Company. ISBN0-8053-9055-3.
Ledgard, Henry (1983). Ada: An Introduction (seconded.). Springer-Verlag. ISBN0-387-90814-5.
Bjørner, Dines; Oest, Ole N., eds. (1980). Towards a Formal Description of Ada. London: Springer-Verlag. ISBN3-540-10283-3.
This page is based on this Wikipedia article Text is available under the CC BY-SA 4.0 license; additional terms may apply. Images, videos and audio are available under their respective licenses.
