Define Functions in Clojure

Here are some different syntax options for defining functions in Clojure.

Most explicit to most implicit, longest to shortest. Repetition of the same function body.

Common: defn

The one you'll see the most is with the defn keyword:

(defn is-published? [x]
  (not= "true" (:draft x))

Shorter, Nested: fn

Next choice: Use fn. Shorter. Can be anonymous. Can define and bind within a let expression within defn.

Function signature:

(fn name? [params*] exprs*)

Used in let:

(let [is-published? (fn [x] (not= "true" (:draft x)))])

Fun fact: defn is actually a macro for:

(def is-published? 
  (fn [x] (not= "true" (:draft x)))

Anonymous: #

No outer parens. No name, ever. No named params:

(let is-published? #(not= "true" (:draft %)))