Clojure 速成

Clojure-tutorial.md

為什麼要用 Clojure 語言來開發軟體？

在 Clojure 社群的一個說法：「同樣的工程師使用 Java 來開發軟體、使用 Nodejs 來開發軟體、使用 Clojure 來開發同樣軟體所花費的時間，大約是：5:3:1。」

Part 1: Basic

lesson 1: syntax

0. truth, math, string

1. Intros to list, vector, map, set

2. conj: conj list ,conj vector ,conj map ,conj set

3. Intros to sequence, function

• first, second, last
• rest
• function

lesson 2: 函數與控制結構

1. function 的練習 double down https://4clojure.oxal.org/#/problem/15

2. if 的練習 https://4clojure.oxal.org/#/problem/162 判斷 nil value https://4clojure.oxal.org/#/problem/134

3. 教 map/filter/reduce

• map 讓你把對「純量」定義的變換，改成對「向量」來定義
• filter 讓你對「線性集合」來做篩選
• reduce -> monoid 的概念 map https://4clojure.oxal.org/#/problem/17 filter https://4clojure.oxal.org/#/problem/18 reduce https://4clojure.oxal.org/#/problem/64

繪圖來說明、函數是如何運作的。 reduce 要使用「魚骨圖」

lesson 3: 區域變數

0. 教 let https://4clojure.oxal.org/#/problem/36 https://4clojure.oxal.org/#/problem/35

1. 教 vector destructuring https://4clojure.oxal.org/#/problem/52

2. 教 map destructuring

3. 教 non-destructuring 的方式取得 collection 的內容

   • nth, get
   • keyword as function

lesson 4: recursive

1. vocabulary: when / dec /inc
2. simple recursive
   https://4clojure.oxal.org/#/problem/57
3. 條件判斷: empty?, zero?, nil?, contains?
4. 容器操作: concat, merge
5. 寫遞迴函數三原則：
   1. 要去想，什麼是終止條件
   2. 要去想，怎麼遞迴　
   3. 在做 informal reasoning 的時候，要切換 purpose view
6. recursive 與「數學歸納法」的關系~
7. 函數命名原則
8. 費波納西 & memoize

相關練習：
Last
https://4clojure.oxal.org/#/problem/19

Penultimate
https://4clojure.oxal.org/#/problem/20

Nth
https://4clojure.oxal.org/#/problem/21

Count a sequence
https://4clojure.oxal.org/#/problem/22

Reverse a sequence
https://4clojure.oxal.org/#/problem/23

lesson 5 sequence

• 解釋解題的原則
  1. Solve the question by remembering the Clojure function name. For example,
     frequencies.
  2. Solve the question by using some sequence questions: map, filter
  3. Solve the question by using advanced sequence skill: dec dimension (mapcat), inc dimension (range)
  4. Solve the question by using reduce.
  5. Solve the question by using recursion.
  6. Solve the question by using mutual recursion. (interpreter)
• Abstraction level: 以 BFS 為例，考慮以下列三種不同的方式來實作
  • Imperative Programming
  • Functional Programming - immutable collection/sequence abstraction & library
  • Declarative Programming - treewalk interpreter & DSL/ leverage embedded SQL
• 解釋 seq abstraction 的重要性, 比較 lodash library

Part 2: Local Environment

lesson 6 開發環境

1. git
2. neovim
3. tmux
4. clj-kondo
5. cljfmt
6. babashka
7. sdkman (用來安裝 java)
8. Clojure CLI

lesson 7 REPL-driven development

1. Conjure
2. vim-sexp
3. go to definition

Part 3: Real World

lesson 8 program structure & side effects

1. namespace, require, def, defn
2. 何謂 side effects: slurp, print
3. Dependency Injection
4. lazy evaluation 與 dorun

;; write a hello world using babashka

lesson 9 literals, format, and hash-map

1. EDN format, edn/read-string
2. string, keyword, symbol
3. the manipulation of hash-map assoc, dissoc, merge, empty, into, zipmap

;; write a CLI program reading config.edn

lesson 10 idioms & skills

1. variable naming: x, xs, coll, m, ms, f
2. Tree manipulation: postwalk
3. Functional programming 常用函數： mapcat, partition, group-by, apply

;; write a CLI program using above skill

lesson 11 debug

1. Clojure error message
2. How to debug

lesson 12 a real world case study

• 以實際案例來學習
• walking skeleton first
• 最常用的一些 libraries:
  • read config files
  • http request
  • SQL database
  • basic web backend steup
• CheatSheet
• neil

Reference

• ClojureBridge_Tutorial
• 我的 Clojure 學習之路

Online REPL for quick start

• https://replit.com/