【译】5分钟入门Nim编程语言
Nim(原名Nimrod)是一种静态类型的命令式编程语言，
Nim语言高效、有表现力、优雅。
# 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。
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