当然，你也可以使用 Qualified class instance creation，只是因为 Java 有 inner class 自动绑定上父域类的状态而已
@Override public Iterator<Boolean> iterator() {return new Clock().new ClockIterator();}

然后我们还可以去写一个更 precious 的 Clock，它不仅会 Tick tock 还能记录时间，它被称为：TimedClock

也很简单，代码里几乎不需要什么修改

（这里明显不是教你怎么用 Generator，因为 yield 太简单了很多人章口就莱，是教你们怎么用 Iterator + switch 在 Java8 里手动写基于状态 🐔 的 Generator）

#code #Java

也相当鬼畜，不过还没有教到使用 switch 进行自由控制流跳转的局面，待会会为大家做现场的表演~

修一下 bug、增加 Tick Thock，下面有更加 excited 的 clock。

#code #java

然后大概是这样

最后我们还有一个最搞基的 Stream：

它的逻辑类似：

function *excitedGenerator() {
yield 3;
yield 2;
yield 1;
// Go!

for (let x of [1,2,3]) yield (Math.trunc(Math.random() * 100) * x)
let clock = new TimedClock();
yield *clock;
}

我们要使用裸 Java，不使用编译器的 suspend function 支持自己手写出来这种 Iterable！

#Java #code Most excited 🐸

那么看来，手写基于状态 🐔 的 Generator 好不好用啊？

准确的说，是”很“不好用...
推荐不要使用，就用 ES6、Kotlin 的 Generator 好了，Generator 还有 async 函数，都是现在不可或缺的语言特性呢。

async 函数，就是说以顺序编程的思路写基于异步/回调的程序逻辑，所谓这么『同步地』写，正是基于可随时挂起继续的协程

async () => {
  let f = await readFile("foo.ext");
  let pst = await parseFile(f);
  await showUI(pst);
}

语法糖后面藏着的其实是随时可以挂起的 async() =>

readFile("foo.ext").then(
  (f) => parseFile(f).then (
    (pst) => showUI(pst);
  );
);

我执行一个异步任务，挂起等待，等待异步任务回调我这个可随时暂停恢复执行的 Generator，然后再来进行下一步操作，等价这么写嵌套的 Promise then

当然，协程也是分对称非对称的，不过都主要是理论，对称协程可以随便 yield 控制权，非对称只有 creator 可以把执行权交回子协程，非对称协程可以实现对称协程。

#CS

https://github.com/duangsuse/Essay-Java8-CST-Based-Generators #GItHub

= 程序设计语言类型::常见名词 #PL #PLT

🤔 有的时候看见诸如王垠这样的人的博客都会感觉好大佬的样子呢。
什么 soundness、completeness、type checker、intersection type、product type... 满嘴是我们这些菜鸡听不懂的 dalao 词汇，一瞬瞎眼膜拜。

其实你只是不明觉厉，这些都是类似”加盐“一样半俗半释的词：比如 Product Type，它其实也没有什么特殊的，只不过说某种 type 是其他一些 type 的融合罢了，看完下面的文字你很快就会明白这些常用名词的含义

要说真正困难的东西，那当然是线性代数莫属喽，给你每个名词的解释你都不一定能弄懂。

为了帮助你们学习这些程序语言类型领域的名词，首先我们得对程序设计语言的抽象语义、解释器、类型检查等概念有个基础的认识。
本教程主要面向刚入门的萌新快速上手，不会提及某些搞基的函数式语言诸如 Scala / Haskell / Agda 的搞基类型特性，比如 Higher-ranked polymorphism, Existential types, Coinducative data types

下面是本期学习到的名词，看起来好高大上呢。

+ [for type checkers] Soundness and completeness
+ Duck/Statically typed, explicitly(implicitly) typed, weakly/strongly typed
+ Type inference / type inferer
+ Types and values
+ Type erasure [Parametric polymorphism]
+ Type constructor
+ Type conversion
+ (Homogenus) Product type
+ Sum type
+ Subtyping
+ Paramized types (Parametric polymorphism)
+ Zero size types (aka. Unit types)
+ Empty types / Bottom type
+ Traits
+ Dependent type

== 什么是类型

不得不引用某 Haskell Values/Types 理论的简易入门了。

类型是什么呢？如果讨论上下文是 C、Java、Kotlin、Dart 这类简单的语言，类型可以被视为集合，某一个位置所有可能出现的值(value)的集合（有时候也可以被说成阶，但其实还是集合方便理解）

Java 的 boolean 就是 true 或者 false

boolean 是类型，true 和 false 是值

比如，有一个函数 abstract void acceptBoolean(boolean b);

实际上是说它”接受所有“ boolean 集合里的值 — true、false

这样就给我们的操作（比如二元运算、值传递、赋值语句等）定义了一个限制 — boolean 类型的参数只能被传入 boolean 类型的东西（变量、常量...）、boolean 类型的本地变量只能被赋值为 boolean....

类型系统的本意关于模块化、安全和优化 — 安全和优化是共生的，因为 Java 是安全的语言，不能让程序因为索引越界这种弱智问题导致更坏的结果，所以 Java 要做很多检查，类型检查，无论编译时或是运行时都一样，而把运行时的开销提升到编译期显然可以使得开销更小，而利用类型系统共生的多态（polymorphism）特性，诸如子类型多态、函数重载、类型转换多态、参数化类型等，可以大大提升程序的抽象性，使得软件工程更方便易读易维护。

比如 Java 的 int 就是一些数字，从 -Integer.MAX_VALUE 数到 Integer.MAX_VALUE...
Java 的 String 虽然是一种 product type，但是也可以认为是一个集合： "a" / "ab" / "ac" / "duangsuse" ....

=== 类型架构器

类型构造器就是接受类型，返回类型的玩意

Kotlin 里的 ? 是一种类型构造器，比如：
Int? 里的 ? 接受一个 kotlin.Int 类型，返回一个 kotlin.Int? 类型（Int? 是 Int 的父类型，因为它可以是 null，或者说 Int? 是 Int 和 Nothing? 的 Union type，在类型层面上是的）

此外，Java 5 引入的 Generics 也是一种类型构造器

java.util.ArrayList<T> 接受一个 T 类型，返回一个 ArrayList<T> 类型
java.util.function.Consumer<T> 接受一个 T 类型，返回一个 Consumer<T> 类型

== first-class 是什么意思

在程序设计语言理论的上下文中，说某个概念是 ”first-class“ 的（有的人也是说”作为值“，其实也都差不多，毕竟值也基本都是 first-class）

+ 可以被作为『函数』（子程序）的参数或者返回值
+ 可以被存储到诸如本地变量这样的容器里

不然的话，就被称为非 first-class (non first class)

== 组合和类型

— Haskell
inc :: Int -> Int
inc n = n +1

这是利用 (+) 操作符和两个 Int 构建的一个计算，(+) 的类型是：

(+) :: Int -> Int -> Int

给它两个 Int，然后它会返回一个 Int — 简单的 Int 二元运算

== Type constructor

A type constructor is a feature of a typed formal language that builds new types from old ones. Basic types are considered to be built using nullary type constructors. Some type constructors take another type as an argument, e.g., the constructors for product types, function types, power types and list types. New types can be defined by recursively composing type constructors.

For example, simply typed lambda calculus can be seen as a language with a single type constructor—the function type constructor (→). Product types can generally be considered "built-in" in typed lambda calculi via currying.

搞🐔一点的东西，毕竟我也不是只 🐔（是的，🐔 是一种 🥬🐔 但是 🥬🐔 不是一种 🐔[1]），没有办法理解也自然不可能误人子弟了，我只是来做乡村怨̶妇̶基础科普... 咳咳
基本都是用 Haskell、Scala、Agda、ML 这类要命 🐸的语言写一点可能并不简单的程序时候需要了解的，不过说起来类型上面讨论的毕竟还是一个高层抽象...

只能给个链接。

+ Kinds

A kind is the type of a type constructor or, less commonly, the type of a higher-order type operator.
A kind system is essentially a simply typed lambda calculus "one level up", endowed with a primitive type, denoted ∗ and called "type", which is the kind of any data type which does not need any type parameters.

===
Abstractly, a type constructor is an n-ary type operator taking as argument zero or more types, and returning another type.
Making use of currying, n-ary type operators can be (re)written as a sequence of applications of unary type operators.
Therefore, we can view the type operators as a simply typed lambda calculus, which has only one basic type, usually denoted ∗, and pronounced "type", which is the type of all types in the underlying language, which are now called proper types in order to distinguish them from the types of the type operators in their own calculus, which are called kinds.

e.g.

Maybe :: * -> *
String :: *
Maybe String :: *
(->) :: TYPE q -> TYPE r -> *

constructed types

show :: Show a => a -> String
(/) :: Fractional a => a -> a -> a

+ Union type

Union types are types describing values that belong to either of two types. For example, in C, the signed char has a -128 to 127 range, and the unsigned char has a 0 to 255 range, so the union of these two types would have an overall "virtual" range of -128 to 255 "(-128, 128] ∪ (0, 256]" that may be used partially depending on which union member is accessed.

operations on a union type are operations that are valid on both types being unioned.

|for example, both String and Int have an toString(): String operator, so type (String ∪ Int) can have toString(): String operator valid too
|but String have an subsequence(Int, Int): CharSequence operator, which is missing from Int, implies type type (String ∪ Int) cannot have the same subsequence operator from String

|As an widely-used example in Kotlin, Any? is union type of Any! and Nothing? (Any ∪ Nothing?)

In a subclassing hierarchy, the union of a type and an ancestor type (such as its parent) is the ancestor type.

|sealed class Ast<out T> { // parent Ast

, ancestor type for Add and Lit


|  abstract fun eval(): T
|  data class Add<T : Number>(val left: Ast<T>, val right: Ast<T>): Ast<T>() { override fun eval() = (left.eval().toInt() + right.eval().toInt()) as T }
|  data class Lit(val x: Int): Ast<Int>() { override fun eval() = x }
|}

>>> Ast.Add(Ast.Lit(2), Ast.Lit(3))

Add(left=Lit(x=2), right=Lit(x=3))

>>> typealias A = Ast.Add<Int>
>>> typealias L = Ast.Lit
>>> A(L(2), L(3))
Add(left=Lit(x=2), right=Lit(x=3))
>>> A(L(2), L(3)).eval()

//=> 5

The union of sibling types is a subtype of their common ancestor (that is, all operations permitted on their common ancestor are permitted on the union type, but they may also have other valid operations in common).

|for the example above, union of sibling types (Add<T> and Lit)'s common ancestor is Ast<out T>, making Add#eval and Lit#eval avaliable.

+ Intersection type

Intersection types are types describing values that belong to both of two other given types with overlapping value sets.

For example, in most implementations of C the signed char has range -128 to 127 and the unsigned char has range 0 to 255, so the intersection type of these two types would have range 0 to 127. Such an intersection type could be safely passed into functions expecting either signed or unsigned chars, because it is compatible with both types.

Intersection types are useful for describing overloaded function's types: for example, if "int → int" is the type of functions taking an integer argument and returning an integer, and "float → float" is the type of functions taking a float argument and returning a float, then the intersection of these two types (int->int ∩ float->float) can be used to describe functions that do one or the other, based on what type of input they are given. Such a function could be passed into another function expecting an "int → int" function safely (is a parent type of both i->i; f->f); it simply would not use the "float → float" functionality.

In a subclassing hierarchy, the intersection of a type and an ancestor type (such as its parent) is the most derived type. The intersection of sibling types is empty.

e.g. (String ∩ CharSequence) is String (note that String is a subtype of CharSequence)
for the Ast<out T> example above, (Ast.Add ∩ Ast.Lit) is Ast<T> (Ast.Lit, Ast.Add is a subtype of Ast, intersection of a type and an ancestor type (Ast) is the most derived type)

+ GADT (Generalized algebraic data type)

[1]: 此梗不是梗，参考 subtyping，子类型

#linux #sysadmin #fedora 原来我现在用的发行版本已经 EOL 了... 🤪

DuangSUSE@duangsuse.moe

 OS: 

Fedora

 
 Kernel: 

x86_64 Linux 5.0.4-200.fc29.x86_64

 Uptime: 

23m

 Packages: 

4863

 Shell: 

zsh 5.6.2

 Resolution: 

1920x1080

 DE: 

KDE 5.55.0 / Plasma 5.14.5

 WM: 

KWin

 WM Theme: 

Breeze Dark

 GTK Theme: 

Windows8 [GTK2/3]

 Icon Theme: 

Adwaita

 Font: 

Abyssinica SIL Regular

 CPU: 

Intel Core i5-7500 @ 4x 3.8GHz [27.8°C]

 GPU: 

nouveaufb

 RAM: 

1799MiB / 3894MiB

手工工加粗粗... 🤪 忍不住想到锤子 🔨 的声控”工作站“

[DuangSUSE@duangsuse]~%

sudo btrfs subvolume list /

ID 257 gen 378914 top level 5 path RootFileSystem
ID 258 gen 378914 top level 5 path Home
ID 398 gen 378825 top level 257 path var/lib/portables
ID 402 gen 378825 top level 257 path var/lib/machines

[DuangSUSE@duangsuse]~%

sudo btrfs filesystem df -h /

Data, single: total=100.01GiB, used=98.40GiB
System, single: total=4.00MiB, used=16.00KiB
Metadata, single: total=3.01GiB, used=2.00GiB
GlobalReserve, single: total=210.84MiB, used=0.00B

说到电子语音，国内某些辣鸡程序员的语音合成实现基本就是个自动控制的播放器，基本不涉及语音学和信号处理内容，质量非常辣鸡... 稍微好点的也不会用机器学习算法尝试让声音『自然』一点，还是简单调音高时长 shift