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Clojure was created in 2007 by Rich Hickey. It's a modern Lisp dialect targeting the JVM (also JavaScript via ClojureScript). Designed around immutable data and pure functions, with first-class concurrency primitives.

Clojure code is data — programs are written as nested lists. The first element is the function, the rest are arguments:

(println "Hello, Clojure!")

That's a list with two elements: the function println and the string "Hello, Clojure!". Parentheses define lists; lists define calls.

Basic arithmetic looks unfamiliar at first — it's also function calls:

(+ 1 2 3)         ; 6
(* 2 (+ 3 4))     ; 14
(- 10 3 2)        ; 5

Semicolons start line comments. ;; is conventional for full-line comments, ; for inline.