Clojure

Rich Hickey is the creator of the Clojure language. and three earlier attempts to provide interoperability between Lisp and Java: a Java foreign language interface for Common Lisp (jfli), A Foreign Object Interface for Lisp (FOIL), and a Lisp-friendly interface to Java Servlets (Lisplets). Hickey started working on Clojure in 2005 and spent about two and a half years working on Clojure before releasing it publicly in October 2007, much of that time working exclusively on Clojure with no outside funding. Stephanie Hickey, his wife, helped to design the language by a being an active listener and participating in discussions without writing any code. At the end of this time, Hickey sent an email announcing the language to some friends in the Common Lisp community. Clojure's name, according to Hickey, is a word play on the programming concept "closure" incorporating the letters C, L, and J for C#, Lisp, and Java respectively—three languages which had a major influence on Clojure's design. == Design ==

Rich Hickey developed Clojure because he wanted a modern Lisp for functional programming, symbiotic with the established Java platform, and designed for concurrency. Clojure's approach to state is characterized by the concept of identities, The community uses tools such as Clojure command-line interface (CLI) Clojure supports multimethods and for interface-like abstractions has a protocol based polymorphism and data type system using records, providing high-performance and dynamic polymorphism designed to avoid the expression problem. Clojure has support for lazy sequences and encourages the principle of immutability and persistent data structures. As a functional language, emphasis is placed on recursion and higher-order functions instead of side-effect-based looping. Automatic tail call optimization is not supported as the JVM does not support it natively; it is possible to do so explicitly by using the recur keyword. For parallel and concurrent programming Clojure provides software transactional memory, a reactive agent system, Clojure 1.7 introduced reader conditionals by allowing the embedding of Clojure, ClojureScript and ClojureCLR code in the same namespace. == Extensible Data Notation ==

Extensible Data Notation, or edn, is a subset of the Clojure language intended as a data transfer format. It can be used to serialize and deserialize Clojure data structures, and Clojure itself uses a superset of edn to represent programs. edn is used in a similar way to JSON or XML, but has a relatively large list of built-in elements, shown here with examples: • booleans: true, false • strings: "foo bar" • characters: \c, \tab • symbols: name • keywords: :key • integers: 123 • floating point numbers: 3.14 • lists: (a b 42) • vectors: [a b 42] • maps: {{code|{:a 1, "foo" :bar, [1 2 3] four}|clojure}} • sets: {{code|#{a b [1 2 3]}|clojure}} • nil: nil (a null-like value) In addition to those elements, it supports extensibility through the use of tags, which consist of the character # followed by a symbol. When encountering a tag, the reader passes the value of the next element to the corresponding handler, which returns a data value. For example, this could be a tagged element: {{code|#myapp/Person {:first "Fred" :last "Mertz"}|clojure}}, whose interpretation will depend on the appropriate handler of the reader. This definition of extension elements in terms of the others avoids relying on either convention or context to convey elements not included in the base set. == Alternative platforms ==

The primary platform of Clojure is Java, which compiles to ECMAScript 3 (or newer ES5 or ES5-strict, up to ES-2021, and ES-next possible) and ClojureCLR, a full port on the .NET platform, interoperable with its ecosystem. Other implementations of Clojure on different platforms include: • Babashka, Native Clojure scripting language leveraging GraalVM native image and Small Clojure Interpreter • ClojureDart, Extend Clojure's reach to mobile & desktop apps by porting Clojure to Dart and Flutter • Clojerl, Clojure on BEAM, the Erlang virtual machine • basilisp, A Clojure-compatible(-ish) Lisp dialect targeting Python 3.8+ • ClojureRS, Clojure on Rust • Ferret, compiles to self-contained C++11 that can run on microcontrollers • jank, Native Clojure hosted in C++ on an LLVM-based JIT • Joker, an interpreter and linter written in Go == Tools ==

Tooling for Clojure development has seen significant improvement over the years. The following is a list of some popular IDEs and text editors with plug-ins that add support for programming in Clojure: • Emacs, with CIDER • IntelliJ IDEA, with Cursive (a free license is available for non-commercial use) • Sublime Text, with Clojure Sublimed, or Tutkain, • Vim, with fireplace.vim, vim-elin, or Conjure (Neovim only) • Visual Studio Code, with Calva • IDE-agnostic: clojure-lsp as a Language Server; clj-kondo as a linter (also used by clojure-lsp) In addition to the tools provided by the community, the official Clojure command-line interface (CLI) tools have also become available on Linux, macOS, and Windows since Clojure 1.9. == Development ==

The development process is restricted to the Clojure core team, though issues are publicly visible at the Clojure JIRA project page. Anyone can ask questions or submit issues and ideas at ask.clojure.org. If it's determined that a new issue warrants a JIRA ticket, a core team member will triage it and add it. JIRA issues are processed by a team of screeners and finally approved by Rich Hickey. == Impact ==

With continued interest in functional programming, Clojure's adoption by software developers using the Java platform has continued to increase. The language has also been recommended by software developers such as Brian Goetz, Eric Evans, James Gosling, Paul Graham, and Robert C. Martin. ThoughtWorks, while assessing functional programming languages for their Technology Radar, described Clojure as "a simple, elegant implementation of Lisp on the JVM" in 2010 and promoted its status to "ADOPT" in 2012. In the "JVM Ecosystem Report 2018" (which was claimed to be "the largest survey ever of Java developers"), that was prepared in collaboration by Snyk and Java Magazine, ranked Clojure as the 2nd most used programming language on the JVM for "main applications". Clojure is used in industry by firms such as Apple, Atlassian, Funding Circle, Netflix, Nubank, Puppet, and Walmart as well as government agencies such as NASA. It has also been used for creative computing, including visual art, music, games, and poetry. In the 2023 edition of Stack Overflow Developer Survey, Clojure was the fourth most admired in the category of programming and scripting languages, with 68.51% of the respondents who have worked with it last year saying they would like to continue using it. In the desired category, however it was marked as such by only 2.2% of the surveyed, whereas the highest scoring JavaScript was desired by 40.15% of the developers participating in the survey. == Release history ==