Clojure (, like closure) is a dynamic and functional dialect of the Lisp programming language on the Java platform.
Like most other Lisps, Clojure's syntax is built on that are first parsed into data structures by a reader before being compiled. Clojure's Lisp reader supports literal syntax for hash table, sets and vectors along with lists, and these are compiled to the mentioned structures directly. Clojure treats Homoiconicity and has a Lisp macro system. Clojure is a Lisp-1 and is not intended to be code-compatible with other dialects of Lisp, since it uses its own set of data structures incompatible with other Lisps.
Clojure advocates immutable object and immutable data structures and encourages programmers to be explicit about managing identity and its states. This focus on programming with immutable values and explicit progression-of-time constructs is intended to facilitate developing more robust, especially concurrent, programs that are simple and fast. While its type system is entirely Type system, recent efforts have also sought the implementation of a Dependent type.
The language was created by Rich Hickey in the mid-2000s, originally for the Java platform; the language has since been ported to other platforms, such as the Common Language Runtime (.NET). Hickey continues to lead development of the language as its benevolent dictator for life.
Hickey 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. 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.
Clojure's approach to state is characterized by the concept of identities, which are represented as a series of immutable states over time. Since states are immutable values, any number of workers can operate on them in parallel, and concurrency becomes a question of managing changes from one state to another. For this purpose, Clojure provides several mutable , each having well-defined semantics for the transition between states.
Clojure runs on the Java platform and as a result, integrates with Java and fully supports calling Java code from Clojure, and Clojure code can be called from Java, too. The community uses tools such as Clojure command-line interface (CLI) or Leiningen for project automation, providing support for Apache Maven integration. These tools handle project package management and dependencies and are configured using Clojure syntax.
As a Lisp dialect, Clojure supports functions as first-class objects, a read–eval–print loop (REPL), and a macro system. Clojure's Lisp macro system is very similar to that of Common Lisp with the exception that Clojure's version of the backquote (termed "syntax quote") qualifies symbols with their namespace. This helps prevent unintended name capture, as binding to namespace-qualified names is forbidden. It is possible to force a capturing macro expansion, but it must be done explicitly. Clojure does not allow user-defined reader macros, but the reader supports a more constrained form of syntactic extension. 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 evaluation and encourages the principle of immutable object 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, and channel-based concurrent programming.
Clojure 1.7 introduced reader conditionals by allowing the embedding of Clojure, ClojureScript and ClojureCLR code in the same namespace. Transducers were added as a method for composing transformations. Transducers enable higher-order functions such as map and fold to generalize over any source of input data. While traditionally these functions operate on sequences, transducers allow them to work on channels and let the user define their own models for transduction.
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:
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: #myapp/Person {:first "Fred" :last "Mertz"}, 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.
Other implementations of Clojure on different platforms include:
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.
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. It could possibly be attributed to limited professional opportunities for Clojure developers with just over 50 search results for "Clojure developer" at the U.S. section of Indeed, as of May 2024.
Initial public release | ||
1.0 | First stable release | |
1.1 | Futures | |
1.2 | Protocols | |
1.3 | Enhanced primitive support | |
1.4 | Reader literals | |
1.5 | Reducers | |
1.5.1 | Fixing a memory leak | |
1.6 | Java API, improved hashing algorithms | |
1.7 | Transducers, reader conditionals | |
1.8 | Additional string functions, direct linking, socket server | |
1.9 | Integration with spec, command-line tools | |
1.10 | Improved error reporting, Java compatibility | |
1.10.1 | Working around a Java performance regression and improving error reporting from clojure.main | |
1.10.2 | Java interoperability/compatibility improvements and other important language fixes | |
1.10.3 | prepl support for reader conditionals | |
1.11.0 | New syntax for keyword argument invocation, new clojure.math namespace, namespace aliasing without loading, and new helper functions added to clojure.core | |
1.11.1 | Rolling back unintended change in binary serialisation of objects of types clojure.lang.Keyword and clojure.lang.ArraySeq. | |
Fix for CVE-2024-22871 Denial of Service vulnerability | ||
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