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Clojure is what happens when a pragmatist designs a Lisp. Rich Hickey created it to bring Lisp's power — homoiconicity, macros, REPL-driven development — to the JVM ecosystem, with immutable data structures and built-in concurrency primitives. The result is a language that's surprisingly practical despite the parentheses.
Immutability is the default. Data structures don't change — you create new versions. This eliminates entire categories of concurrency bugs and makes state management predictable. Clojure's persistent data structures use structural sharing, making immutable operations efficient. The REPL-driven workflow (evaluate code interactively, build programs incrementally) is addictive once experienced.
Clojure's ecosystem includes ClojureScript (compiles to JavaScript), Datomic (an immutable database by the same creator), and a mature set of libraries. Companies like Nubank (Latin America's largest fintech), Walmart, and Cisco use Clojure in production. The community is small but deeply knowledgeable — Clojure developers tend to be experienced programmers who chose the language deliberately.