Your First Program

Create a file named hello.clj:

(println "Hello, world!")
(println "Welcome to Clojure.")

Run it:

clj -M hello.clj

Expected output

Hello, world!
Welcome to Clojure.

• (println "Hello, world!") is a list: the first item is the function to call, the rest are its arguments.
• Strings use double quotes only.
• No semicolons, no main function: Clojure reads and runs a file one expression at a time, from top to bottom.

Printing several values

(println "Answer:" 42)
(println 1 2 3)
(println (str "no space " "here"))
(print "no newline")
(println)
(prn "prn shows quotes" [1 "two" :three])

Answer: 42
1 2 3
no space here
no newline
"prn shows quotes" [1 "two" :three]

• println separates its arguments with spaces and ends the line.
• str joins values into one string.
• print doesn't add a new line; (println) prints just one.
• prn prints values as data — strings keep their quotes — which is handy for debugging.

Expressions return values

(println (+ 1 2))
(println (* 6 7))
(println (str "Clojure " (+ 1 0) "." (* 3 4)))

3
42
Clojure 1.12

Everything in Clojure is an expression that produces a value; you nest expressions to combine them.

Practice

Write a program that prints your name on one line and your favorite food on the next.

(println "Ada")
(println "Pizza")

Ada
Pizza