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44-520: Erlang ( / ˈ ɜːr l æ ŋ / UR -lang ) is a general-purpose , concurrent , functional high-level programming language , and a garbage-collected runtime system . The term Erlang is used interchangeably with Erlang/OTP, or Open Telecom Platform (OTP), which consists of the Erlang runtime system , several ready-to-use components (OTP) mainly written in Erlang, and a set of design principles for Erlang programs. The Erlang runtime system

88-457: A benchmark with 20 million processes was successfully performed with 64-bit Erlang on a machine with 16 GB random-access memory (RAM; total 800 bytes/process). Erlang has supported symmetric multiprocessing since release R11B of May 2006. While threads need external library support in most languages, Erlang provides language-level features to create and manage processes with the goal of simplifying concurrent programming. Though all concurrency

132-437: A general purpose programming language.  For example, COBOL , Fortran , and Lisp were created as DSLs (for business processing, numeric computation, and symbolic processing), but became GPL's over time. Inversely, a language may be designed for general use but only applied in a specific area in practice. A programming language that is well suited for a problem, whether it be general-purpose language or DSL, should minimize

176-773: A general-purpose language with an appropriate library of data types and functions for the domain may be used instead. While DSLs are usually smaller than GPL in that they offer a smaller range of notations of abstractions, some DSLs actually contain an entire GPL as a sublanguage. In these instances, the DSLs are able to offer domain-specific expressive power along with the expressive power of GPL. General Purpose programming languages are all Turing complete , meaning that they can theoretically solve any computational problem. Domain-specific languages are often similarly Turing complete but are not exclusively so. General-purpose programming languages are more commonly used by programmers. According to

220-1024: A lot of money to build a large scale message handling system that really had to be up all the time, could never afford to go down for years at a time, I would unhesitatingly choose Erlang to build it in. Erlang is the programming language used to code WhatsApp . It is also the language of choice for Ejabberd – an XMPP messaging server. Elixir is a programming language that compiles into BEAM byte code (via Erlang Abstract Format). Since being released as open source, Erlang has been spreading beyond telecoms, establishing itself in other vertical markets such as FinTech, gaming, healthcare, automotive, Internet of Things and blockchain. Apart from WhatsApp, there are other companies listed as Erlang's success stories, including Vocalink (a MasterCard company), Goldman Sachs , Nintendo , AdRoll, Grindr , BT Mobile , Samsung , OpenX , and SITA . A factorial algorithm implemented in Erlang: A tail recursive algorithm that produces

264-409: A mechanism that makes it easy for external processes to monitor for crashes (or hardware failures), rather than an in-process mechanism like exception handling used in many other programming languages. Crashes are reported like other messages, which is the only way processes can communicate with each other, and subprocesses can be spawned cheaply (see below ). The "let it crash" philosophy prefers that

308-418: A module in memory at the same time, and processes can concurrently run code from each. The versions are referred to as the "new" and the "old" version. A process will not move into the new version until it makes an external call to its module. An example of the mechanism of hot code loading: For the second version, we add the possibility to reset the count to zero. Only when receiving a message consisting of

352-515: A new process that takes over the old process's task. The official reference implementation of Erlang uses BEAM . BEAM is included in the official distribution of Erlang, called Erlang/OTP. BEAM executes bytecode which is converted to threaded code at load time. It also includes a native code compiler on most platforms, developed by the High Performance Erlang Project (HiPE) at Uppsala University . Since October 2001

396-406: A process be completely restarted rather than trying to recover from a serious failure. Though it still requires handling of errors, this philosophy results in less code devoted to defensive programming where error-handling code is highly contextual and specific. A typical Erlang application is written in the form of a supervisor tree. This architecture is based on a hierarchy of processes in which

440-607: A result, though it was first used by its creators to rewrite the kernel of the Unix operating system, it was easily adapted for use in application development, embedded systems (e.g., microprocessor programming), video games (e.g., Doom ), and so on. Today, C remains one of the most popular and widely-used programming languages. Conceived as an extension to C, C++ introduced object-oriented features, as well as other conveniences like references, operator overloading, and default arguments. Like C, C++'s generality allowed it to be used in

484-465: A study, C , Python , and Java were the most commonly used programming languages in 2021.  One argument in favor of using general-purpose programming languages over domain-specific languages is that more people will be familiar with these languages, overcoming the need to learn a new language. Additionally, for many tasks (e.g., statistical analysis, machine learning, etc.) there are libraries that are extensively tested and optimized. Theoretically,

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528-1056: A system with process isolation, limited (controlled) interaction between processes may still be allowed over inter-process communication (IPC) channels such as shared memory , local sockets or Internet sockets . In this scheme, all of the process' memory is isolated from other processes except where the process is allowing input from collaborating processes. System policies may disallow IPC in some circumstances. For example, in mandatory access control systems, subjects with different sensitivity levels may not be allowed to communicate with each other. The security implications in these circumstances are broad and span applications in network key encryption systematics as well as distributed caching algorithms. Interface-defined protocols such as basic cloud access architecture and network sharing are similarly affected. Operating systems that support process isolation by providing separate address spaces for each process include: Internet Explorer 4 used process isolation in order to allow separate windowed instances of

572-459: A wide range of areas. While its C++'s core area of application is in systems programming (because of C++'s ability to grant access to low-level architecture), it has been used extensively to build desktop applications, video games, databases, financial systems, and much more. Major software and finance companies, such as Microsoft , Apple , Bloomberg , and Morgan Stanley , still widely use C++ in their internal and external applications. Python

616-589: Is a set of different hardware and software technologies designed to protect each process from other processes on the operating system . It does so by preventing process A from writing to process B. Process isolation can be implemented with virtual address space , where process A's address space is different from process B's address space – preventing A from writing onto B. Security is easier to enforce by disallowing inter-process memory access, in contrast with less secure architectures such as DOS in which any process can write to any memory in any other process. In

660-543: Is designed for systems with these traits: The Erlang programming language has immutable data, pattern matching , and functional programming . The sequential subset of the Erlang language supports eager evaluation , single assignment , and dynamic typing . A normal Erlang application is built out of hundreds of small Erlang processes. It was originally proprietary software within Ericsson , developed by Joe Armstrong , Robert Virding, and Mike Williams in 1986, but

704-475: Is explicit in Erlang, processes communicate using message passing instead of shared variables, which removes the need for explicit locks (a locking scheme is still used internally by the VM). Inter-process communication works via a shared-nothing asynchronous message passing system: every process has a "mailbox", a queue of messages that have been sent by other processes and not yet consumed. A process uses

748-399: Is less than Pivot ." ++ is the list concatenation operator. A comparison function can be used for more complicated structures for the sake of readability. The following code would sort lists according to length: A Pivot is taken from the first parameter given to qsort() and the rest of Lists is named Rest . Note that the expression is no different in form from (in

792-404: Is not named in the first definition of qsort , which deals with the base case of an empty list and thus has no need of this function, let alone a name for it. Erlang has eight primitive data types : And three compound data types: Two forms of syntactic sugar are provided: Erlang has no method to define classes, although there are external libraries available. Erlang is designed with

836-429: The receive primitive to retrieve messages that match desired patterns. A message-handling routine tests messages in turn against each pattern, until one of them matches. When the message is consumed and removed from the mailbox the process resumes execution. A message may comprise any Erlang structure, including primitives (integers, floats, characters, atoms), tuples, lists, and functions. The code example below shows

880-457: The BEAM virtual machine (VM), which compiles Erlang to C using a mix of natively compiled code and threaded code to strike a balance between performance and disk space. According to co-inventor Joe Armstrong, the language went from laboratory product to real applications following the collapse of the next-generation AXE telephone exchange named AXE-N in 1995. As a result, Erlang was chosen for

924-485: The Fibonacci sequence : Omitting the comments gives a much shorter program. Quicksort in Erlang, using list comprehension : The above example recursively invokes the function qsort until nothing remains to be sorted. The expression [Front || Front <- Rest, Front < Pivot] is a list comprehension , meaning "Construct a list of elements Front such that Front is a member of Rest , and Front

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968-597: The browser their own processes; however, at the height of the browser wars , this was dropped in subsequent versions to compete with Netscape Navigator (which sought to concentrate upon one process for the entire Internet suite). This idea of process-per-instance would not be revisited until a decade afterwards, when tabbed browsing became more commonplace. In Google Chrome 's " Multi-Process Architecture " and Internet Explorer 8 's " Loosely Coupled IE (LCIE) ", tabs containing webpages are contained within their own semi-separate OS-level processes which are isolated from

1012-451: The 1960s: GPSS and Simula for discrete event simulation; MAD , BASIC , Logo , and Pascal for teaching programming; C for systems programming; JOSS and APL\360 for interactive programming. The distinction between general-purpose programming languages and domain-specific programming languages is not always clear. A programming language may be created for a specific task, but used beyond that original domain and thus be considered

1056-514: The HiPE system is fully integrated in Ericsson's Open Source Erlang/OTP system. It also supports interpreting, directly from source code via abstract syntax tree , via script as of R11B-5 release of Erlang. Erlang supports language-level Dynamic Software Updating . To implement this, code is loaded and managed as "module" units; the module is a compilation unit . The system can keep two versions of

1100-412: The appropriate action to correct the error condition. Erlang's main strength is support for concurrency . It has a small but powerful set of primitives to create processes and communicate among them. Erlang is conceptually similar to the language occam , though it recasts the ideas of communicating sequential processes (CSP) in a functional framework and uses asynchronous message passing. Processes are

1144-411: The atom code_switch will the loop execute an external call to codeswitch/1 ( ?MODULE is a preprocessor macro for the current module). If there is a new version of the counter module in memory, then its codeswitch/1 function will be called. The practice of having a specific entry-point into a new version allows the programmer to transform state to what is needed in the newer version. In the example,

1188-466: The built-in support for distributed processes: As the example shows, processes may be created on remote nodes, and communication with them is transparent in the sense that communication with remote processes works exactly as communication with local processes. Concurrency supports the primary method of error-handling in Erlang. When a process crashes, it neatly exits and sends a message to the controlling process which can then take action, such as starting

1232-912: The implementation of Erlang was open-sourced and most of the Erlang team resigned to form a new company, Bluetail AB. Ericsson eventually relaxed the ban and re-hired Armstrong in 2004. In 2006, native symmetric multiprocessing support was added to the runtime system and VM. Erlang applications are built of very lightweight Erlang processes in the Erlang runtime system. Erlang processes can be seen as "living" objects ( object-oriented programming ), with data encapsulation and message passing , but capable of changing behavior during runtime. The Erlang runtime system provides strict process isolation between Erlang processes (this includes data and garbage collection, separated individually by each Erlang process) and transparent communication between processes (see Location transparency ) on different Erlang nodes (on different hosts). Joe Armstrong, co-inventor of Erlang, summarized

1276-898: The language. Erlang, together with libraries and the real-time distributed database Mnesia , forms the OTP collection of libraries. Ericsson and a few other companies support Erlang commercially. General-purpose programming language Early programming languages were designed for scientific computing (numerical calculations) or commercial data processing, as was computer hardware. Scientific languages such as Fortran and Algol supported floating-point calculations and multidimensional arrays, while business languages such as COBOL supported fixed-field file formats and data records . Much less widely used were specialized languages such as IPL-V and LISP for symbolic list processing ; COMIT for string manipulation; APT for numerically controlled machines . Systems programming requiring pointer manipulation

1320-438: The level of detail required while still being expressive enough in the problem domain. As the name suggests, general-purpose language is "general" in that it cannot provide support for domain-specific notation while DSLs can be designed in diverse problem domains to handle this problem. General-purpose languages are preferred to DSLs when an application domain is not well understood enough to warrant its own language. In this case,

1364-474: The lifecycle of their child processes, and this includes handling situations in which those child processes crash. Any process can become a supervisor by first spawning a child process, then calling erlang:monitor/2 on that process. If the monitored process then crashes, the supervisor will receive a message containing a tuple whose first member is the atom 'DOWN' . The supervisor is responsible firstly for listening for such messages and secondly, for taking

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1408-501: The next Asynchronous Transfer Mode (ATM) exchange AXD . In February 1998, Ericsson Radio Systems banned the in-house use of Erlang for new products, citing a preference for non-proprietary languages. The ban caused Armstrong and others to make plans to leave Ericsson. In March 1998 Ericsson announced the AXD301 switch, containing over a million lines of Erlang and reported to achieve a high availability of nine "9"s . In December 1998,

1452-624: The presence of these libraries should bridge the gap between general-purpose and domain-specific languages. An empirical study in 2010 sought to measure problem-solving and productivity between GPLs and DSLs by giving users problems who were familiar with the GPL ( C# ) and unfamiliar with the DSL ( XAML ). Ultimately, users of this specific domain-specific language performed better by a factor of 15%, even though they were more familiar with GPL, warranting further research. The predecessor to C , B ,

1496-410: The previous example) except for the use of a comparison function in the last part, saying "Construct a list of elements X such that X is a member of Rest , and Smaller is true", with Smaller being defined earlier as The anonymous function is named Smaller in the parameter list of the second definition of qsort so that it can be referenced by that name within that function. It

1540-412: The primary means to structure an Erlang application. They are neither operating system processes nor threads , but lightweight processes that are scheduled by BEAM. Like operating system processes (but unlike operating system threads), they share no state with each other. The estimated minimal overhead for each is 300 words . Thus, many processes can be created without degrading performance. In 2005,

1584-763: The principles of processes in his PhD thesis : Joe Armstrong remarked in an interview with Rackspace in 2013: "If Java is ' write once, run anywhere ', then Erlang is 'write once, run forever'." In 2014, Ericsson reported Erlang was being used in its support nodes, and in GPRS , 3G and LTE mobile networks worldwide and also by Nortel and Deutsche Telekom . Erlang is used in RabbitMQ . As Tim Bray , director of Web Technologies at Sun Microsystems , expressed in his keynote at O'Reilly Open Source Convention (OSCON) in July 2008: If somebody came to me and wanted to pay me

1628-498: The state is kept as an integer. In practice, systems are built up using design principles from the Open Telecom Platform, which leads to more code upgradable designs. Successful hot code loading is exacting. Code must be written with care to make use of Erlang's facilities. In 1998, Ericsson released Erlang as free and open-source software to ensure its independence from a single vendor and to increase awareness of

1672-428: The top level process is known as a "supervisor". The supervisor then spawns multiple child processes that act either as workers or more, lower level supervisors. Such hierarchies can exist to arbitrary depths and have proven to provide a highly scalable and fault-tolerant environment within which application functionality can be implemented. Within a supervisor tree, all supervisor processes are responsible for managing

1716-507: Was conceived as a language that emphasized code readability and extensibility. The former allowed non-software engineers to easily learn and write computer programs, while the latter allowed domain specialists to easily create libraries suited to their own use cases. For these reasons, Python has been used across a wide range of domains. Below are some of the areas where Python is used: The following are some general-purpose programming languages: Process isolation Process isolation

1760-598: Was designed with the aim of improving the development of telephony applications. The initial version of Erlang was implemented in Prolog and was influenced by the programming language PLEX used in earlier Ericsson exchanges. By 1988 Erlang had proven that it was suitable for prototyping telephone exchanges, but the Prolog interpreter was far too slow. One group within Ericsson estimated that it would need to be 40 times faster to be suitable for production use. In 1992, work began on

1804-467: Was developed largely for a specific purpose: systems programming . By contrast, C has found use in a variety of computational domains, such as operating systems , device drivers , application software , and embedded systems . C is suitable for use in a variety of areas because of its generality. It provides economy of expression, flow control, data structures, and a rich set of operators, but does not constrain its users to use it in any one context. As

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1848-444: Was released as free and open-source software in 1998. Erlang/OTP is supported and maintained by the Open Telecom Platform (OTP) product unit at Ericsson . The name Erlang , attributed to Bjarne Däcker, has been presumed by those working on the telephony switches (for whom the language was designed) to be a reference to Danish mathematician and engineer Agner Krarup Erlang and a syllabic abbreviation of "Ericsson Language". Erlang

1892-406: Was typically done in assembly language , though JOVIAL was used for some military applications. IBM 's System/360 , announced in 1964, was designed as a unified hardware architecture supporting both scientific and commercial applications, and IBM developed PL/I for it as a single, general-purpose language that supported scientific, commercial, and systems programming. Indeed, a subset of PL/I

1936-475: Was used as the standard systems programming language for the Multics operating system. Since PL/I, the distinction between scientific and commercial programming languages has diminished, with most languages supporting the basic features required by both, and much of the special file format handling delegated to specialized database management systems . Many specialized languages were also developed starting in

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