Clojure¶

インストール¶

Windows¶

Linux¶

sudo apt install bash curl rlwrap openjdk-11-jdk
cd /tmp

インストールスクリプトは公式にアクセスして確認した上で最新バージョンを使おう.

cider¶

JDK15ではエラーになる模様.
- 実際 OpenJDK 11 をインストールしたら動くようになった.

ツール類¶

公式ページを参考に~/binにleinまたはlein.batを置く.

Leiningen

ガイド: 参考リンク集¶

Clojure公式
Docs for Functional Tools
- こちらの方が見やすいらしい: ClojureDocs quick reference
- Official docs
- Official docs: core api
日本語版
Clojure By Example
ClojureDocs Quick Reference
Clojure高速化テクニック
- Premature optimization is the root of all evil. -- Donald Knuth
Clojure/ClojureScript関連リンク集
BRAVE CLOJURE BECOME A BETTER PROGRAMMER
Very good: Clojure design patterns
pgarland / algorithms-clojure
okasaki-clojure
https://ayato-p.github.io/clojure-beginner/getting_started/intellij_with_cursive.html
Reagent

ガイド: 関数プログラミングの学習のために¶

Edabit has lots and lots of coding exercises. They're small. They're clearly explained. They are graded Very Easy to Expert. Use these challenges as a way to practice your functional programming skills. See if you can solve the same problem in different ways by applying different skills.

Project Euler

Project Euler has amassed many programming challenges. They are often very mathematical, but everything is clearly explained. The great thing about these challenges is that they will force you to face real limits. For instance, figuring out the first 10 prime num-bers is easy. Figuring out the 1,000,000th prime number before the sun dies out is a real challenge! You'll face memory limitations, performance limitations, stack size limitations, and more. All of these limits will force you to make your skills practical and not just theoretical.

CodeWars

CodeWars has a large collection of exercises that are challenging enough to test your skills but small enough to solve in a few minutes. These are great for practicing different skills on the same problem.

Code Katas

Code Katas are a kind of practice where you solve the same problem multiple times. We perform a kata more for practicing the process of programming than for solving some challenge. These are also good because they let you integrate your new functional program-ming skills with your other development skills, such as testing.

2022-05時点でのWeb開発¶

Twitter URL

Pedestal + Duct構成ならこんな感じかな(PedestalとDuctで主要機能をまかなえる)。

HTTP抽象: Pedestal

ルーティング: Pedestal

入力バリデーション: malli

RDBアクセス: next.jdbc + Honey SQL

ライフサイクル管理: Duct (Integrant)

設定: Duct

clojure.spec強化: Orchestra, Expound

Leiningen: GitHubのレポジトリを指定する¶

Clojure CLI (deps.edn) でも対応できるらしい.
参考
profiles.cljに次のように追記
- {:user {:plugins [[lein-git-deps "0.0.2-SNAPSHOT"]]}}
project.clj に次のように追記(:dependenciesと同じインデントになるように)
- :git-dependencies [["https://github.com/tobyhede/monger.git"]]

MySQL接続¶

cf.
- clojure-doc.org
- clojure.github.io
- ~/junk/clojure/todo-clj
MySQLでtodo_clj_devを作っておくこと: CREATE DATABASE todo_clj_dev
仮定: dbuser=root, dbpass=""
- あとでの設定で効いてくる: 必要に応じて書き換える

project.clj¶

(defproject todo-clj "0.1.0-SNAPSHOT"
  :description "FIXME: write description"
  :url "http://example.com/FIXME"
  :license {:name "Eclipse Public License"
            :url "http://www.eclipse.org/legal/epl-v10.html"}
  :dependencies [[org.clojure/clojure "1.11.1"]
                 [org.clojure/clojure-contrib "1.2.0"]
                 [org.clojure/java.jdbc "0.7.12"]
                 [mysql/mysql-connector-java "8.0.29"]])

sample.clj¶

(ns todo-clj.sample
  (:require [hiccup.core :as hc]
            [hiccup.page :as hp]
            [clojure.java.jdbc :as jdbc]
            [clojure.test :refer :all]))
(require '[clojure.java.jdbc :as jdbc])

(def db-spec {:dbtype "mysql" :dbname "todo_clj_dev" :host "localhost" :port 3306 :user "root" :password ""})
(jdbc/db-do-commands
 db-spec
 (jdbc/drop-table-ddl :member))
(jdbc/db-do-commands
 db-spec
 (jdbc/create-table-ddl :member
                        [[:id :int :primary :key "AUTO_INCREMENT"] [:name "varchar(20)" "not null"] [:age :int] [:address "varchar(100)"]]
                        {:table-spec "ENGINE=InnoDB" :entities clojure.string/lower-case}))
(do
  (jdbc/insert! db-spec :member {:name "phasetr"})
  (jdbc/insert! db-spec :member {:name "foo"})
  (jdbc/insert-multi! db-spec :member [{:name "alice" :address "wonderland"} {:name "cheshire"} {:name "mad hatter"}]))

REPLで役立つ関数¶

参考
- doc, find-doc, apropos, dir, source, pst

REPLを再起動せずにリフレッシュする¶

参考
projece.cljで:dependencies [[org.clojure/tools.namespace "1.1.0"] ]を指定する.
lein depsを実行してインストールする.
REPL内で次のコマンドを実行する.

1	`(do (use '[clojure.tools.namespace.repl :only (refresh)]) (refresh))`

印字・print¶

四種類ある.

	人間が読む	機械が読む
改行あり	println	prn
改行なし	print	pr

関数に引数をリストで渡す: Schemeとの比較¶

参考URL

Schemeの場合.

gosh> ((lambda x (print x)) "foo")
(foo)
#<undef>

gosh> ((lambda (x) (print x)) "foo")
foo

Clojureで括弧なしでリストで渡す方法.

1	`(defn [& args] (println args))`

関数・マクロのリファレンス¶

`#?@$`¶

参考
条件つきスプライシングリーダーマクロ.

(defn build-list []
  (list #?@(:clj  [5 6 7 8]
            :cljs [1 2 3 4])))

defmulti¶

doc
(defmulti name docstring? attr-map? dispatch-fn & options)

defmethod¶

doc
(defmethod multifn dispatch-val & fn-tail)

juxt¶

doc

;; Extract values from a map, treating keywords as functions.
((juxt :a :b) {:a 1 :b 2 :c 3 :d 4})
;;=> [1 2]

;; sort list of maps by multiple values
(sort-by (juxt :a :b) [{:a 1 :b 3} {:a 1 :b 2} {:a 2 :b 1}])
;;=> [{:a 1 :b 2} {:a 1 :b 3} {:a 2 :b 1}]

((juxt + * min max) 3 4 6)
;;=> [13 72 3 6]

;; split a sequence into two parts
user=> ((juxt take drop) 3 [1 2 3 4 5 6])
;; => [(1 2 3) (4 5 6)]

sort-by¶

doc

user=> (sort-by count ["aaa" "bb" "c"])
("c" "bb" "aaa")

user=> (sort-by first [[1 2] [2 2] [2 3]])
([1 2] [2 2] [2 3])

user=> (sort-by first > [[1 2] [2 2] [2 3]])
([2 2] [2 3] [1 2])

簡単コメント¶

セミコロンによるコメントアウト以外のコメントアウト法がある.
#_をフォームまたはシンボルの前につけると, そのフォームまたはシンボルがコメントアウトされる.

記号へのリファレンス¶

[参考ページ(https://japan-clojurians.github.io/clojure-site-ja/guides/weird_characters){target=_blank}

作ったファイルを別のファイルにインポートする¶

下のように(ns)に(:gen-class)を書いておく.

(ns fdg.prologue
  (:gen-class)
  (:require [sicmutils.env :as e :refer :all]))

この状態でこのフォームを評価して, インポートしたいファイルでrequireなり何なりすればよい.

リストの処理: `doseq`, `for`¶

参考
doseqはnilを返す: prnなど副作用発生が前提
forは値を返してくれる.

(doseq [letter [:a :b]
        number (range 3)] ; 0, 1, 2の要素を持つリスト
  (prn [letter number]))

(for [letter [:a :b]
      number (range 3)] ; 0, 1, 2の要素を持つリスト
  [letter number])