Clojure Macros Cheat Sheet

(defmacro unless [test then else]  `(if (not ~test) ~then ~else))(unless false  (println "runs")  (println "does not run"));; expands to:;; (if (not false) (println "runs") (println "does not run"))

(def x 10)'(1 2 x)     ;; => (1 2 x)          — quote: no evaluation`(1 2 ~x)    ;; => (1 2 10)         — syntax-quote + unquote evaluates x`(1 2 ~@[3 4 5]) ;; => (1 2 3 4 5)  — splices a sequence into the list(defmacro my-and  ([] true)  ([x] x)  ([x & rest] `(if ~x (my-and ~@rest) ~x)))

;; Auto-gensym: any symbol ending in # inside `...` gets a unique suffix(defmacro my-or [a b]  `(let [val# ~a]     (if val# val# ~b)))(my-or false 42) ;; => 42, and `val#` can't collide with a caller's `val`;; Manual gensym for more control(defmacro my-swap! [a b]  (let [tmp (gensym "tmp")]    `(let [~tmp ~a]       (reset! ~a ~b)       (reset! ~b ~tmp))))

(macroexpand-1 '(unless false (println "a") (println "b")));; => (if (clojure.core/not false) (println "a") (println "b"))(macroexpand '(my-or false 42));; fully expands nested macros too, useful for threading/-> style macros;; clojure.walk/macroexpand-all expands everything recursively(require '[clojure.walk :as walk])(walk/macroexpand-all '(my-or false (my-or nil 1)))