Functional JavaScript 筆記

Functional JavaScript

目錄

• 1 Get Started with FP
• 2 First-class Functions and Applicative Programming
• 3 Variable Scope and Closures
• 4 High-order Functions
• 5 Function-Building Functions
• 6 Recursion
• 7 Purity, Immutability and Policies for Change
• 8 Flow-based Programming
• 9 Programming without Class
• 10 Appendix

Get Started with FP

1. CSV parse:

   return _.reduce(str.split("\n"), function(table, row){

   table.push(_.map(row.split(","), function(cell){return cell.trim();})); return table;}, []); };

2. 作者是ClojureScript的作者？

First-class Functions and Applicative Programming

1. return _.reduceRight(arguments, function(truth,f){ return truth && f(); }, true);
2. 傳遞null作為第一個參數給apply：意味着this引用全局對象...
3. p44 傳統的SQL Select實際上對應關系代數裡的Project
4. JS的lambda文法太麻煩，給寫FP風格的代碼帶來了麻煩

   1. restrict( project( as(library, {ed: 'edition'}), ['title','isbn','edition']),

      function(book){ return book.edition>1; } );

Variable Scope and Closures

High-order Functions

Function-Building Functions

1. function partial(fun ){

   var pargs = _.rest(arguments);

   return function(){

   var args = cat(pargs, _.toArray(arguments));

   return fun.apply(fun, args);

   } }

Recursion

1. trampoline（避免mutual-recursive溢出）：
   1. function even(n){ if(n==0) return true; else return partial1(odd, n-1); }
      1. ==> odd(20000001)()()...();

   2. function trampoline(fun ){

      var result = fun.apply(fun, _.rest(arguments)); //又來了

      while(_.isFunction(result)) result = result();

      return result; }

2. generator（惰性無限序列）
   1. head-tail()抽象，其中，tail封裝了“剩餘序列的計算”

   2. function genTake(n, gen){

      var doTake = function(x, g, ret){ if(x==0)return ret; else return partial(doTake, x-1, genTail(g), cat(ret, genHead(g)));}

      return trampoline(doTake, n, gen, []);

Purity, Immutability and Policies for Change

1. Object#freeze => deepFreeze
2. API：讓對象修改方法傳回新對象執行個體

Flow-based Programming

1. _.chain
2. LazyChain
   1. thunk：a function waiting to be called
   2. #force()
3. jQuery $.Deferred()
4. Pipelining
5. Action（Monad）：flowing in context？
   1. lift
   2. actions

Programming without Class

1. Mixins
   1. var polyToString = dispatch( function(s）{ return _.isString(s)? s : undefined; }, ...

2. var MyMixin = {

   setValue: function(v){ ... this._value = v; this.notify(oldVal, v); }

3. _.extend(MyClass.prototype, MyMixin);
4. var CAS = function(val){ MyClass.call(this, val); }
   1. var CASMixin = ...

Appendix

1. Underscore-contrib
2. RxJS
3. Bilby's multimethods
4. allong.es：support for stateful iterators
5. *Reducers：inspired by Clojure's reducer
6. ClojureScript（作者就是寫《The Joy of Clojure》的？）
7. CoffeeScript
   1. Literate程式設計
   2. Varargs
   3. 清單了解
   4. 解構指派
8. Roy：inspired by ML
9. Elm（+不用作字元串拼接，需要用++）：FRP