kohyama

ファンクタ, アプリカティブ, モナド

はじめに

「そもそも概念が分からない」という方に向けた説明です.
簡略化のため大幅に説明を省略しています. ご容赦ください.
誤りは御指摘いただければ幸いです.

「ファンクタ」, 「アプリカティブ」, 「モナド」 などは Haskell に限定された概念・用語ではありませんが,

kohyama

Clojure tips infrequently used

To get names of methods of a class

(map #(.getName %) (.getMethods java.io.File))
; -> ("equals" "toString" "hashCode" "compareTo" "compareTo" "getName" "length" "getParent" "isAbsolute" "getCanonicalPath" "setReadOnly" "list" "list" "delete" "getParentFile" "getPath" "getAbsolutePath" "getAbsoluteFile" "getCanonicalFile" "toURL" "toURI" "canRead" "canWrite" "exists" "isDirectory" "isFile" "isHidden" "lastModified" "createNewFile" "deleteOnExit" "listFiles" "listFiles" "listFiles" "mkdir" "mkdirs" "renameTo" "setLastModified" "setWritable" "setWritable" "setReadable" "setReadable" "setExecutable" "setExecutable" "canExecute" "listRoots" "getTotalSpace" "getFreeSpace" "getUsableSpace" "createTempFile" "createTempFile" "wait" "wait" "wait" "getClass" "notify" "notifyAll")

kohyama

Clojure ref, atom, agent の要約

• ref (協調的, 同期的)
• atom (非協調的, 同期的)
• agent (非同期的)

ref (協調的, 同期的)

• 作成: ref
• 参照: deref または @

kohyama

(def prime-numbers
  ((fn f [x]
     (cons x
       (lazy-seq
         (f (first
              (drop-while
                (fn [n]
                  (some #(zero? (mod n %))
                    (take-while #(<= (* % %) n) prime-numbers)))
                (iterate inc (inc x))))))))

kohyama

(defn factorize [n]
  ((fn f [n [h & r :as ps]]
     (cond (< n 2) '()
       (zero? (mod n h)) (cons h (lazy-seq (f (quot n h) ps)))
       :else (recur n r)))
   n prime-numbers)))

kohyama

A minimum setting to use browser REPL of ClojureScript

Assumed that you have set leiningen up and can use it.

1. Prepare files

Copy project.clj, repl-test.cljs and brepl-test.html from this gist or git clone this gist and move or copy repl-test.cljs under src directory.

$ git clone https://gist.github.com/6183122.git
$ cd 6183122/

kohyama

Prepare an environment according to A minimum setting to use browser REPL of ClojureScript.
Input lines of dom-example.cljs to the REPL.
Here's a SCREEN CAST.

Enjoy!

kohyama

(def s "(- a b)"))

のような文字列があるとき, 実行時に決まる値で a や b を束縛して, この式を評価したいとする.

(let [a 4 b 3] (eval (read-string s)))

kohyama

(require '[clojure.test :refer (with-test is run-tests)])

(with-test
  (defn tails [coll]
    (take-while seq (iterate rest coll)))

  (is (= (tails '(:a :b :c))
         '((:a :b :c) (:b :c) (:c)))))

kohyama

(require '[clojure.test :refer (with-test are run-tests)])

(with-test
  (defn map-between [f s]
    (map (fn [[a b]] (f a b)) (partition 2 1 s)))

  (are [f s _ r] (= (map-between f s) r)
    #(- %2 %1) '()        -> '()
    #(- %2 %1) '(0)       -> '()
    #(- %2 %1) '(0 1)     -> '(1)