[nim/zh-cn] Add translation (#4282)

zh-cn/nim-cn.html.markdown

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+---
+language: Nim
+filename: learnNim-cn.nim
+contributors:
+    - ["Jason J. Ayala P.", "http://JasonAyala.com"]
+    - ["Dennis Felsing", "http://felsin9.de/nnis/"]
+translators:
+    - ["lzw-723", "https://github.com/lzw-723"]
+lang: zh-cn
+---
+
+Nim(原名Nimrod)是一种静态类型的命令式编程语言，
+它能在不影响运行时效率的情况下为程序员提供强大的功能。
+
+Nim语言高效、有表现力、优雅。
+
+```nim
+# 单行注释以一个#开头
+
+#[
+  这是多行注释
+  在Nim语言中，多行注释可以嵌套，以#[开头，以]#结尾
+]#
+
+discard """
+这也可以作为多行注释使用。
+或者用于无法解析、损坏的代码
+"""
+
+var                     # 声明(和赋值)变量
+  letter: char = 'n'    # 带或不带类型批注
+  lang = "N" & "im"
+  nLength: int = len(lang)
+  boat: float
+  truth: bool = false
+
+ let            # 使用let*一次性*声明和绑定变量。
+  legs = 400   # legs是不可改变的。
+  arms = 2_000 # _会被忽略，对long类型非常有用。
+  aboutPi = 3.15
+
+const            # 常量在编译时计算。这确保了
+  debug = true   # 性能，在编译时表达式中很有用。
+  compileBadCode = false
+
+when compileBadCode:            # `when`是编译时的`if`
+  legs = legs + 1               # 这个错误永远不会被编译。
+  const input = readline(stdin) # const在编译时必须是已知的。
+
+discard 1 > 2 # 注意：如果表达式的结果未使用，
+              # 编译器会发出警告。`discard`绕过了这一点。
+
+
+#
+# 数据结构
+#
+
+# 元组(Tuple)
+
+var
+  child: tuple[name: string, age: int]   # 元组有*字段名*
+  today: tuple[sun: string, temp: float] # 和*顺序*
+
+
+child = (name: "Rudiger", age: 2) # 使用字面值()一次性赋值全部
+today.sun = "Overcast"            # 也可以单独赋值
+today.temp = 70.1
+
+# 序列(Sequence)
+
+var
+  drinks: seq[string]
+
+drinks = @["Water", "Juice", "Chocolate"] # @[V1,..,Vn] 是序列的字面值
+
+drinks.add("Milk")
+
+if "Milk" in drinks:
+  echo "We have Milk and ", drinks.len - 1, " other drinks"
+
+let myDrink = drinks[2]
+
+#
+# 自定义类型
+#
+
+# 定义你自己的类型使得编译器为你工作。
+# 这使得静态类型变得强大和有用。
+
+type
+  Name = string # 类型别名为你提供一个新类型，
+  Age = int     # 该类型可与旧类型互换，但更具描述性。
+  Person = tuple[name: Name, age: Age] # 也可以定义数据结构。
+  AnotherSyntax = tuple
+    fieldOne: string
+    secondField: int
+
+var
+  john: Person = (name: "John B.", age: 17)
+  newage: int = 18 # 在这里使用Age比int要好
+
+john.age = newage # 仍然有效，因为int和Age同义
+
+type
+  Cash = distinct int    # `distinct`使一个新类型与它的基本类型不兼容。
+  Desc = distinct string
+
+var
+  money: Cash = 100.Cash # `.Cash`把int转换成我们的类型
+  description: Desc  = "Interesting".Desc
+
+when compileBadCode:
+  john.age  = money        # 错误！age是int类型、money是Cash类型
+  john.name = description  # 编译器说：“没门！”
+
+#
+# 更多类型和数据结构
+#
+
+# 枚举类型只能具有有限数量的值之一
+
+type
+  Color = enum cRed, cBlue, cGreen
+  Direction = enum # 可选格式
+    dNorth
+    dWest
+    dEast
+    dSouth
+var
+  orient = dNorth # `orient`的类型是Direction，值是`dNorth`
+  pixel = cGreen # `pixel`的类型是Color，值是`cGreen`
+
+discard dNorth > dEast # Enum通常是“序数”类型
+
+# 子范围指定有限的有效范围
+
+type
+  DieFaces = range[1..20] # 只有从1到20的int才是有效值
+var
+  my_roll: DieFaces = 13
+
+when compileBadCode:
+  my_roll = 23 # 错误！
+
+# 数组(Array)
+
+type
+  RollCounter = array[DieFaces, int]  # 数组长度固定
+  DirNames = array[Direction, string] # 以任意有序类型索引
+  Truths = array[42..44, bool]
+var
+  counter: RollCounter
+  directions: DirNames
+  possible: Truths
+
+possible = [false, false, false] # 数组字面以[V1,..,Vn]表示
+possible[42] = true
+
+directions[dNorth] = "Ahh. The Great White North!"
+directions[dWest] = "No, don't go there."
+
+my_roll = 13
+counter[my_roll] += 1
+counter[my_roll] += 1
+
+var anotherArray = ["Default index", "starts at", "0"]
+
+# 可用的数据结构包括表、集合、列表、队列、压缩前缀树。
+# http://nim-lang.org/docs/lib.html#collections-and-algorithms
+
+#
+# IO和控制流
+#
+
+# `case`, `readLine()`
+
+echo "Read any good books lately?"
+case readLine(stdin)
+of "no", "No":
+  echo "Go to your local library."
+of "yes", "Yes":
+  echo "Carry on, then."
+else:
+  echo "That's great; I assume."
+
+# `while`, `if`, `continue`, `break`
+
+import strutils as str # http://nim-lang.org/docs/strutils.html
+echo "I'm thinking of a number between 41 and 43. Guess which!"
+let number: int = 42
+var
+  raw_guess: string
+  guess: int
+while guess != number:
+  raw_guess = readLine(stdin)
+  if raw_guess == "": continue # 跳出循环
+  guess = str.parseInt(raw_guess)
+  if guess == 1001:
+    echo("AAAAAAGGG!")
+    break
+  elif guess > number:
+    echo("Nope. Too high.")
+  elif guess < number:
+    echo(guess, " is too low")
+  else:
+    echo("Yeeeeeehaw!")
+
+#
+# 循环(Iteration)
+#
+
+for i, elem in ["Yes", "No", "Maybe so"]: # 也可以是`for elem in`
+  echo(elem, " is at index: ", i)
+
+for k, v in items(@[(person: "You", power: 100), (person: "Me", power: 9000)]):
+  echo v
+
+let myString = """
+an <example>
+`string` to
+play with
+""" # 多行字符串
+
+for line in splitLines(myString):
+  echo(line)
+
+for i, c in myString:       # 索引和字符。或使用'for j in'只有字符
+  if i mod 2 == 0: continue # 紧凑的'if'形式
+  elif c == 'X': break
+  else: echo(c)
+
+#
+# 过程(Procedure)
+#
+
+type Answer = enum aYes, aNo
+
+proc ask(question: string): Answer =
+  echo(question, " (y/n)")
+  while true:
+    case readLine(stdin)
+    of "y", "Y", "yes", "Yes":
+      return Answer.aYes  # 枚举类型可以
+    of "n", "N", "no", "No":
+      return Answer.aNo
+    else: echo("Please be clear: yes or no")
+
+proc addSugar(amount: int = 2) = # amount默认是2，不返回任何值
+  assert(amount > 0 and amount < 9000, "Crazy Sugar")
+  for a in 1..amount:
+    echo(a, " sugar...")
+
+case ask("Would you like sugar in your tea?")
+of aYes:
+  addSugar(3)
+of aNo:
+  echo "Oh do take a little!"
+  addSugar()
+# 这里不需要使用`else` 。只能是`yes`和`no`。
+
+#
+# 外部函数接口(FFI)
+#
+
+# 因为Nim可以编译为C，使用外部函数接口(FFI)很简单：
+
+proc strcmp(a, b: cstring): cint {.importc: "strcmp", nodecl.}
+
+let cmp = strcmp("C?", "Easy!")
+```
+
+除此以外，Nim通过元编程、性能和编译时特性将自己与其他同类分离开来。
+
+## 进阶阅读
+
+* [主页](http://nim-lang.org)
+* [下载](http://nim-lang.org/download.html)
+* [社区](http://nim-lang.org/community.html)
+* [常见问题](http://nim-lang.org/question.html)
+* [文档](http://nim-lang.org/documentation.html)
+* [参考手册](http://nim-lang.org/docs/manual.html)
+* [标准库](http://nim-lang.org/docs/lib.html)
+* [Rosetta Code](http://rosettacode.org/wiki/Category:Nim)