Functional JavaScript

目录

• 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. 传递null作为第一个参数给apply：意味着this引用全局对象...
3. p44 传统的SQL Select实际上对应关系代数里的Project
4. JS的lambda语法太麻烦，给写FP风格的代码带来了麻烦
   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 /*, pargs */){

   var pargs = _.rest(arguments);

   return function(/* arguments */){

   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 /*, args */){

      var result = fun.apply(fun, _.rest(arguments)); //又来了

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

      return result; }

2. generator（惰性无限序列）
   1. head-tail()抽象，其中，tail封装了“剩余序列的计算”
   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：让对象修改方法返回新对象实例

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（作者就是写《The Joy of Clojure》的？）
7. CoffeeScript
   1. Literate编程
   2. Varargs
   3. 列表理解
   4. 解构赋值
8. Roy：inspired by ML
9. Elm（+不用作字符串拼接，需要用++）：FRP