CLOJURE WORKSHOP

RECURSION

(defn length ([collection] (length collection 0)) ([collection accumulator] (if (empty? collection) accumulator (recur (rest collection) (inc accumulator)))))

(loop [x 10]  (when (> x 1)    (println x)    (recur (- x 2))))

SEQUENCE PROCESSING

(defn  balance    ([string]      (balance  0  (seq  string)))    ([count  [head  &  tail  :as  chars]]      (if  (not  (empty?  chars))          (case  head              \(  (recur  (inc  count)  tail)              \)  (if  (zero?  count)                        false                        (recur  (dec  count)  tail))              (recur  count  tail))          true)))

RECURSIVE

(defn-‐match  balance    ([?string]                          (balance  0  (seq  string)))    ([_            []                    ]  true)    ([?count  [\(  &  ?tail]]  (balance  (inc  count)  tail))    ([0            [\)  &  _]        ]  false)    ([?count  [\)  &  ?tail]]  (balance  (dec  count)  tail))    ([?count  [_    &  ?tail]]  (balance  count  tail)))

PATTERN MATCHING

(defn  balance  [string]    (-‐>>  string            seq            (map  {\(  inc  \)  dec})            (filter  identity)            (reductions  #(%2  %1)  0)            (filter  neg?)            empty?))

SEQUENCE PROCESSING

PROTOCOLS

(defrecord  CartesianCoordinate  [x  y])

(defrecord  PolarCoordinate  [distance  angle])

(defprotocol  Moveable    (move-‐north  [self  amount])    (move-‐east    [self  amount]))

(extend-‐type  CartesianCoordinate

   Moveable

   (move-‐north  [{x  :x  y  :y}  ammount]        (CartesianCoordinate.  (+  x  ammount)  y))

   (move-‐east  [{x  :x  y  :y}  ammount]        (CartesianCoordinate.  x  (+  y  ammount))))

(defrecord  CenterPointRectangle  [center-‐point  width  height])

(defrecord  CornerPointRectangle  [top-‐left  bottom-‐right])

(extend-‐type  CenterPointRectangle      Moveable

   (move-‐north  [self  ammount]        (update-‐in  self  [:center-‐point]                              #(move-‐x  %  ammount)))

   (move-‐east  [self  ammount]        (update-‐in  self  [:center-‐point]                              #(move-‐y  %  ammount))))

MACROS

'(println "Hello, World")

=> (println "Hello, World")'(println "Hello, World")

(first )'(println "Hello, World")

(first )'(println "Hello, World")=> println

function-name(def )'(println "Hello, World")(first )

(list function-name "Goodbye, Cruel World")

function-name(def )'(println "Hello, World")(first )

(list function-name "Goodbye, Cruel World")=> (println "Goodbye, Cruel World")

function-name(def )

(def new-code ) (eval new-code)

(first )'(println "Hello, World")

(list function-name "Goodbye, Cruel World")

function-name(def )

(def new-code ) (eval new-code)

(first )'(println "Hello, World")

(list function-name "Goodbye, Cruel World")

prints: “Goodbye, Cruel World”

(defmacro emoify [original-code] (let [ ]  (emoify (println "Hello, World"))

function-name (first )'(println "Hello, World")(list function-name "Goodbye, Cruel World")

(defmacro emoify [original-code] (let [ ]  (emoify (println "Hello, World"))

function-name (first )'(println "Hello, World")(list function-name "Goodbye, Cruel World")

prints: “Goodbye, Cruel World”

FINQuestions?