sw-samuraj

(ns blog-map-reduce.core
  (:import java.security.MessageDigest))

(defn digest [string]
  "Returns a SHA-1 digest of the given string."
  (.digest (MessageDigest/getInstance "SHA-1")
           (.getBytes string)))

(defn hex [bt]
  "Returns a hexadecimal value of the given byte."

sw-samuraj

(defn catalan [n]
  "Counts a Catalan number by recursion."
  (loop [cnt n acc 1]
    (if (zero? cnt)
      acc
      (recur (dec cnt)
             (* acc (- 4 (/ 6 (inc cnt))))))))

sw-samuraj

(defn factorial [n]
  "Counts a factorial."
  (reduce *' (range 1 (inc n))))

(defn binomial [n k]
  "Counts a binomial coefficient."
  (/ (factorial n)
     (*' (factorial k)
         (factorial (- n k)))))

sw-samuraj

(def static-var "static var")

static-var
;; -> "static var"

(binding [static-var "re-binded var"] static-var)
;; -> IllegalStateException Can't dynamically bind non-dynamic var:
;;              user/static-var clojure.lang.Var.pushThreadBindings (Var.java:320)

sw-samuraj

(defn cube [x] (Math/pow x 3))

(defn cube-root [x] (Math/pow x 1/3))

(defn ^:dynamic prettify [x] (Math/round x))

(defn compute [] (prettify (cube-root (cube 42))))

(compute)
;; -> 42

sw-samuraj

(def ^:dynamic *dynamic-var* "dynamic var")

*dynamic-var*
;; -> "dynamic var"

(def re-binded-var
  (binding [*dynamic-var* "re-binded var"] *dynamic-var*))

re-binded-var
;; -> "re-binded var"

sw-samuraj

(future (def future-var "future var"))

future-var
;; -> "future var"

sw-samuraj

;; the initial namespace in REPL is 'user'

(def my-var "var in the user namespace")

(ns new-namespace)

my-var
;; -> CompilerException java.lang.RuntimeException:
;;          Unable to resolve symbol: my-var in this context

sw-samuraj

def spicy = { first, second, third ->
    println "I like food with $first, $second and $third."
}

def curry = spicy.curry("curry")
def moreCurry = curry.curry("curry")
def curryAndChilli = moreCurry.curry("chilli")

curryAndChilli.call()
// prints:

sw-samuraj

(defn spicy [first second third]
  (println "I like food with" first "," second "and" third "."))

(def curry (partial spicy "curry"))

(def more-curry (partial curry "curry"))

(def curry-and-chilli (partial more-curry "chilli"))

(curry-and-chilli)