Clojure functions exercises

cl_functions.clj

;; https://clojure.org/guides/learn/functions#_test_your_knowledge

; defn
(defn greet [] (println "Hello"))

; def fn
(def greet (fn [] (println "Hello")))

; def with #
(def greet #(println "Hello"))

; (greet)

;;;;;;;;;

(defn greeting 
    ([] (greeting "World"))
    ([x] (greeting "Hello" x))
    ([x y] (str x ", " y "!"))
)

;; For testing
(assert (= "Hello, World!" (greeting)))
(assert (= "Hello, Clojure!" (greeting "Clojure")))
(assert (= "Good morning, Clojure!" (greeting "Good morning" "Clojure")))

;;;;

(defn do-nothing [x] (identity x))
(do-nothing 2)

;;;
(defn always-thing [& y] (identity :thing))
(always-thing 1 2 3 4 5)

;;;

(defn make-thingy [x] (fn [& this] (identity x)))

;; Tests
(let [n (rand-int Integer/MAX_VALUE)
      f (make-thingy n)]
  (assert (= n (f)))
  (assert (= n (f :foo)))
  (assert (= n (apply f :foo (range)))))

;;
(defn triplicate [f] (dotimes [x 3] (apply f [])))

;;
(defn opposite [f]
    (fn [& args] (not (apply f args))))

;;
(defn triplicate2 [f & args]
    (triplicate (fn [] (apply f args))))

(triplicate2 println "Hello")
;;

(assert (= (Math/cos Math/PI) -1.0))

(let [n (rand-int Integer/MAX_VALUE)]
    (assert (= (+ (Math/pow (Math/sin n) 2) (Math/pow (Math/cos n) 2) ) 1.0))
)

;;
(defn http-get [url]
    (let [jurl (java.net.URL. url)]
        (slurp (.openStream jurl))
    )
)
  
(assert (.contains (http-get "http://www.w3.org") "html"))

;;
(defn one-less-arg [f x]
    (fn [& args] (apply f x args)))

;;
(defn two-fns [f g]
    (fn [x] (f (g x)))
)