Clojure: Syntax, Immutability & the Seq Abstraction

Clojure is a modern, functional Lisp dialect running primarily on the JVM -- immutability and simplicity are central design goals, with seamless interoperability with existing Java libraries.

Lisp Syntax: Code as Nested Lists

(+ 1 2 3)  ; => 6 -- the function comes FIRST, inside parens

(defn greet [name]
  (str "Hello, " name "!"))

(greet "Alice")  ; => "Hello, Alice!"

Immutability by Default

(def original [1 2 3])
(def updated (conj original 4))

original  ; => [1 2 3] -- unchanged
updated   ; => [1 2 3 4] -- a NEW vector

; Persistent data structures share unchanged internal structure
; between old/new versions -- not a naive full copy on every change,
; making immutability practically efficient at real-world scale

Keywords & Map Lookup

(def person {:name "Alice" :age 30})

(:name person)   ; => "Alice" -- keyword used AS a function
(get person :age) ; => 30 -- equivalent, more explicit form

The Seq Abstraction: One API, Many Collections

; The SAME map function works across a vector, a list, and a set --
; no separate specialized version needed per collection type
(map inc [1 2 3])    ; => (2 3 4)
(map inc '(1 2 3))   ; => (2 3 4)
(map inc #{1 2 3})   ; => (2 3 4)