Clojure Cheat Sheet

Clojure syntax, immutable data structures, persistent collections, and functional idioms for modern concurrent JVM programming.

2 PagesAdvancedMar 28, 2026

Basic Syntax

Bindings, control flow, and printing.

clojure

(def age 30)(def name "Ada")(def pi 3.14159)(if (>= age 18)  (println name "is an adult")  (println name "is a minor"))(doseq [i (range 5)]  (println "Count:" i))

Collections

Persistent vectors, maps, and sequence functions.

clojure

(def nums [5 3 1 4 2])            ; vector (immutable)(def evens (filter even? nums))    ; (4 2)(def squared (map #(* % %) nums))  ; (25 9 1 16 4)(def total (reduce + nums))        ; 15(def sorted (sort nums))           ; (1 2 3 4 5)(def person {:name "Ada" :age 30}) ; map literal(:name person)                     ; "Ada", keyword-as-function lookup(assoc person :age 31)             ; returns new map, original unchanged

Concurrency Primitives

Managed references for shared state.

clojure

(def counter (atom 0))              ; mutable reference, synchronous updates(swap! counter inc)                 ; atomically increments@counter                            ; deref, reads current value => 1(def account (ref 100))             ; coordinated (STM) reference(dosync  (alter account - 30))             ; transactional update(future (Thread/sleep 1000) (println "done"))  ; runs on another thread

Core Forms

Common Clojure special forms and macros.

def- binds a symbol to a value in the current namespace
defn- defines a named function
let- creates local bindings scoped to a body of code
fn / #()- anonymous function literal (long and shorthand forms)
atom- uncoordinated, synchronous mutable reference type
->/->>- threading macros that thread a value through function calls
keyword (:key)- self-evaluating symbol commonly used as a map key or accessor

Pro Tip

Use the `->` and `->>` threading macros to flatten deeply nested function calls into a readable top-to-bottom pipeline, instead of reading inside-out.

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