Hello, Clojure

Print “Hello, Clojure!”:

(println "Hello, Clojure!")

Add comments:

;; prints "Hello, Clojure!"
(println "Hello, Clojure!") ; "Hello, Clojure!"

Concatenate strings:

(str "Hello" ", " "Clojure" "!") ; "Hello, Clojure!"

Count the number of characters in a string:

(count "Hello, World!") ; 13

Use arithmetic operations:

(/ (* (+ 4 3) (- 2 3))
   (* (+ 2 3 4)))
;; -7/9

Use truncating division and compute the rest of that division:

(quot 10 3) ; 3
(mod 10 3) ; 1

Compute the power and square root:

(Math/pow 2 10) ; 1024.0
(Math/sqrt 16) ; 4.0

Define and call a function:

(defn say-hi [to-whom]
  (str "Hello, " to-whom "!"))
(say-hi "Jim") ; "Hello, Jim!"

Define and call a function that calculates the hypotenuse of a right-angled triangle:

;; a²+b²=c² <=> c=sqrt(a²+b²)
(defn hypotenuse [a b]
  (Math/sqrt (+ (Math/pow a 2) (Math/pow b 2))))
(hypotenuse 3 4) ; 5.0

Exercises

Circumference of a Rectangle

Write a function circumference that computes the circumference of a rectangle given its sides a and b.

Hint: Use the formula 2ab.

Test: (circumference 3 4) shall return 14.

Solution

(defn circumference [a b]
  (* 2 (+ a b)))

Area of a Circle

Write a function that computes the area of a circle given its radius r.

Hint: Use the constant Math/PI and the formula πr².

Test: (area 2) shall return 12.566370614359172.

Solution

(defn area [r]
  (* Math/PI (Math/pow r 2)))

Minutes and Seconds

Write a function min-sec that formats a given number of seconds to a string of the format xmys, with x being the number of minutes and y the number of (remaining) seconds.

Hint: Use the quot and mod functions for the calculations.

Test: (min-sec 3578) shall return 59m38s.

Solution

(defn min-sec [sec]
  (str (quot sec 60) "m"
       (mod sec 60) "s"))