Clojure is a functional language that runs on the Java Virtual Machine. It is a dialect of LISP. It was designed and implemented by Rich Hickey.

Why learn Clojure?

• Functional programming: no side-effects, no assignments, no mutable data
• Concise syntax
• Powerful functional data structures: lists, vectors, sets, maps
• Anonymous functions (also called closures)
• Higher-order functions (functions can return functions)
• Powerful tools for composing functions: map, reduce, filter
• Interoperability with Java (any Java class/method can be used from Clojure code)
• Macros (code that generates or transforms code: a program add new syntactic forms to the language)
• Interactive, incremental development (the REPL, read-eval-print loop)

Recommended reading: Beating the Averages by Paul Graham: talks about Common LISP, but everything he says about LISP is true of Clojure.

Data types:

• Integers, floating point numbers
• Keywords (:a, :hello): often used as opaque identifiers
• Strings (which are actually Java String objects)
• Lists ('(1 2 3), '(:a :b :c))
• Vectors ([1 2 3], [:a :b :c])
• Sequences (an abstract generalization of lists, vectors, and any other data structure that represents a sequence of values: many built-in functions operate on sequences such as conj, first, rest)
• Sets (#{:a :b :c})
• Maps ({:a 1, :b 2, :c 3})

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