clojure.clj

(def user-info ["robert8990" 2011 :name "Bob" :city "Boston"])
;= #'user/user-info

(let [[username account-year & extra-info] user-info,
      {:keys [name city]} (apply hash-map extra-info)]
  (format "%s is in %s" name city))
;= "Bob is in Boston"
;; This example is equal to below.
(let [[username account-year & {:keys [name city]}] user-info]
  (format "%s is in %s" name city))
;= "Bob is in Boston"

;; hmmm...
;; This one?
(let [[username account-year & extra-info] user-info]
  (println extra-info)
  (println (type extra-info)))
;= (:name Bob :city Boston)
;= clojure.lang.PersistentVector$ChunkedSeq

;; This one?
(let [[username account-year & extra-info] user-info,
      extra-info-map (apply hash-map extra-info)]
  (println extra-info-map)
  (println (type extra-info-map)))
;; {:name Bob, :city Boston}
;; clojure.lang.PersistentHashMap

;; In this case
(def user-info ["robert8990" 2011 :name "Bob" :city "Boston"])
;; We can see like below.(look like?)
["robert8990", 2011          ,{:name "Bob" :city "Boston"}]
[username    , account-year  ,extra-info]

;; We write intuitively
(let [[username account-year & {:keys [name city]}] user-info]
  (format "%s is in %s" name city))
;; Clojure is simple form!><


;; fn or let
;; fn use case. for example...
(map (fn [x] (* x 2))
     [1 2 3])
;= (2 4 6)

(reduce (fn [x, y]
          (+ x y))
        0
        [1 2 3 4 5])
;= 15

;; let use case. for example...
(defn square-adder
  [x, y]
  (let [x2 (* x x), y2 (* y y)] ;=> x2 = x*x; y2 = y*y;
    (+ x2 y2)))
(square-adder 10 20)
;= 500

;; defn or letfn
;; defn use case. for example...
(defn hoge [] (print "hogehoge"))
(hoge)
;= hogehoge

;; letfn use case. for example...
(letfn [(fuga [] (print "fugafuga"))]
  (fuga))
;= fugafuga
(fuga)
;= CompilerException java.lang.RuntimeException: Unable to resolve symbol: fuga in this context, compiling:(NO_SOURCE_PATH:0:0)

;; create lexical scope at letfn!

;; we can referring function document.
(doc doc)
(doc hash-map)
(doc apply)
(doc format)
(doc map)
(doc reduce)


;; by the way
;; We can use Macro, it enable to create NEW SYNTAX.
;; for example. 'my-if'

;; first original 'if'
(if true
  (println "Hello")
  (println "Hi"))
;= Hello
;; don't say "Hi". only "Hello".

;; normally defn...
(defn my-if
  [test, consequest, alternative]
  (if test
    consequest
    alternative))
;; try to use
(def x 10)
(my-if (> x 10) "hoge" "fuga")
;= fuga

;; hmmm...
;; but, this case
(my-if (> x 10)
       (println "hoge")
       (println "fuga"))
;= hoge
;= fuga
;; Oh... I expect only say "fuga".

;; Macro use...
(defmacro mymacro-if
  [test, consequest, alternative]
  (list 'if test
        consequest
        alternative))
;; this using
(def x 10)
(mymacro-if (> x 10) "hoge" "fuga")
;= fuga

;; this one?
(mymacro-if (> x 10)
            (println "hoge")
            (println "fuga"))
;= fuga
;; Yeah!! only say "fuga".