N分钟学习Elixir

文章目录
  1. 1. 注释
  2. 2. 基本类型
  3. 3. 操作符
  4. 4. 控制流
  5. 5. 模块和函数
  6. 6. 结构和异常
  7. 7. 并发

获取代码: learnelixir.ex

Elixir 是构建在Erlang虚拟机上的现代函数编程语言.完全和Erlang兼容,对很多标准语法进行了扩展,并提供了更多的功能.

翻译了一部分发现,已经有中文版了, 在这里

注释

1
# 单行注释以一个#号开始.
# 没有多行注释,但可以注释多行.
# 要使用elixir shell使用`iex`命令.
# 编译模块使用`elixirc`命令.
# 如果elixir正确安装,应该都在PATH中.

基本类型

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# 这些是数字
3    # 整数
0x1F # 整数
3.0  # 浮点数
# Atoms, that are literals, a constant with name. They start with `:`.
# 原子,是字面的,一个命名常量. 以`:`开始.
:hello # atom
# 元组在内存中是连续地存储的
{1,2,3} # tuple
# 可以使用`elem`函数访问一个元组中的元素
elem({1, 2, 3}, 0) #=> 1
# Lists that are implemented as linked lists.
[1,2,3] # list
# We can access the head and tail of a list as follows:
[head | tail] = [1,2,3]
head #=> 1
tail #=> [2,3]
# In elixir, just like in Erlang, the `=` denotes pattern matching and
# not an assignment.
#
# This means that the left-hand side (pattern) is matched against a
# right-hand side.
#
# This is how the above example of accessing the head and tail of a list works.
# A pattern match will error when the sides don't match, in this example
# the tuples have different sizes.
# {a, b, c} = {1, 2} #=> ** (MatchError) no match of right hand side value: {1,2}
# There are also binaries
<<1,2,3>> # binary
# Strings and char lists
"hello" # string
'hello' # char list
# Multi-line strings
"""
I'm a multi-line
string.
"""
#=> "I'm a multi-line\nstring.\n"
# Strings are all encoded in UTF-8:
"héllò" #=> "héllò"
# Strings are really just binaries, and char lists are just lists.
<<?a, ?b, ?c>> #=> "abc"
[?a, ?b, ?c]   #=> 'abc'
# `?a` in elixir returns the ASCII integer for the letter `a`
?a #=> 97
# To concatenate lists use `++`, for binaries use `<>`
[1,2,3] ++ [4,5]     #=> [1,2,3,4,5]
'hello ' ++ 'world'  #=> 'hello world'
<<1,2,3>> <> <<4,5>> #=> <<1,2,3,4,5>>
"hello " <> "world"  #=> "hello world"

操作符

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# Some math
1 + 1  #=> 2
10 - 5 #=> 5
5 * 2  #=> 10
10 / 2 #=> 5.0
# In elixir the operator `/` always returns a float.
# To do integer division use `div`
div(10, 2) #=> 5
# To get the division remainder use `rem`
rem(10, 3) #=> 1
# There are also boolean operators: `or`, `and` and `not`.
# These operators expect a boolean as their first argument.
true and true #=> true
false or true #=> true
# 1 and true    #=> ** (ArgumentError) argument error
# Elixir also provides `||`, `&&` and `!` which accept arguments of any type.
# All values except `false` and `nil` will evaluate to true.
1 || true  #=> 1
false && 1 #=> false
nil && 20  #=> nil
!true #=> false
# For comparisons we have: `==`, `!=`, `===`, `!==`, `<=`, `>=`, `<` and `>`
1 == 1 #=> true
1 != 1 #=> false
1 < 2  #=> true
# `===` and `!==` are more strict when comparing integers and floats:
1 == 1.0  #=> true
1 === 1.0 #=> false
# We can also compare two different data types:
1 < :hello #=> true
# The overall sorting order is defined below:
# number < atom < reference < functions < port < pid < tuple < list < bit string
# To quote Joe Armstrong on this: "The actual order is not important,
# but that a total ordering is well defined is important."

控制流

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# `if` expression
if false do
  "This will never be seen"
else
  "This will"
end
# There's also `unless`
unless true do
  "This will never be seen"
else
  "This will"
end
# Remember pattern matching? Many control-flow structures in elixir rely on it.
# `case` allows us to compare a value against many patterns:
case {:one, :two} do
  {:four, :five} ->
    "This won't match"
  {:one, x} ->
    "This will match and bind `x` to `:two`"
  _ ->
    "This will match any value"
end
# It's common to bind the value to `_` if we don't need it.
# For example, if only the head of a list matters to us:
[head | _] = [1,2,3]
head #=> 1
# For better readability we can do the following:
[head | _tail] = [:a, :b, :c]
head #=> :a
# `cond` lets us check for many conditions at the same time.
# Use `cond` instead of nesting many `if` expressions.
cond do
  1 + 1 == 3 ->
    "I will never be seen"
  2 * 5 == 12 ->
    "Me neither"
  1 + 2 == 3 ->
    "But I will"
end
# It is common to see the last condition equal to `true`, which will always match.
cond do
  1 + 1 == 3 ->
    "I will never be seen"
  2 * 5 == 12 ->
    "Me neither"
  true ->
    "But I will (this is essentially an else)"
end
# `try/catch` is used to catch values that are thrown, it also supports an
# `after` clause that is invoked whether or not a value is caught.
try do
  throw(:hello)
catch
  message -> "Got #{message}."
after
  IO.puts("I'm the after clause.")
end
#=> I'm the after clause
# "Got :hello"

模块和函数

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# Anonymous functions (notice the dot)
square = fn(x) -> x * x end
square.(5) #=> 25
# They also accept many clauses and guards.
# Guards let you fine tune pattern matching,
# they are indicated by the `when` keyword:
f = fn
  x, y when x > 0 -> x + y
  x, y -> x * y
end
f.(1, 3)  #=> 4
f.(-1, 3) #=> -3
# Elixir also provides many built-in functions.
# These are available in the current scope.
is_number(10)    #=> true
is_list("hello") #=> false
elem({1,2,3}, 0) #=> 1
# You can group several functions into a module. Inside a module use `def`
# to define your functions.
defmodule Math do
  def sum(a, b) do
    a + b
  end
  def square(x) do
    x * x
  end
end
Math.sum(1, 2)  #=> 3
Math.square(3) #=> 9
# To compile our simple Math module save it as `math.ex` and use `elixirc`
# in your terminal: elixirc math.ex
# Inside a module we can define functions with `def` and private functions with `defp`.
# A function defined with `def` is available to be invoked from other modules,
# a private function can only be invoked locally.
defmodule PrivateMath do
  def sum(a, b) do
    do_sum(a, b)
  end
  defp do_sum(a, b) do
    a + b
  end
end
PrivateMath.sum(1, 2)    #=> 3
# PrivateMath.do_sum(1, 2) #=> ** (UndefinedFunctionError)
# Function declarations also support guards and multiple clauses:
defmodule Geometry do
  def area({:rectangle, w, h}) do
    w * h
  end
  def area({:circle, r}) when is_number(r) do
    3.14 * r * r
  end
end
Geometry.area({:rectangle, 2, 3}) #=> 6
Geometry.area({:circle, 3})       #=> 28.25999999999999801048
# Geometry.area({:circle, "not_a_number"})
#=> ** (FunctionClauseError) no function clause matching in Geometry.area/1
# Due to immutability, recursion is a big part of elixir
defmodule Recursion do
  def sum_list([head | tail], acc) do
    sum_list(tail, acc + head)
  end
  def sum_list([], acc) do
    acc
  end
end
Recursion.sum_list([1,2,3], 0) #=> 6
# Elixir modules support attributes, there are built-in attributes and you
# may also add custom ones.
defmodule MyMod do
  @moduledoc """
  This is a built-in attribute on a example module.
  """
  @my_data 100 # This is a custom attribute.
  IO.inspect(@my_data) #=> 100
end

结构和异常

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# Structs are extensions on top of maps that bring default values,
# compile-time guarantees and polymorphism into Elixir.
defmodule Person do
  defstruct name: nil, age: 0, height: 0
end
joe_info = %Person{ name: "Joe", age: 30, height: 180 }
#=> %Person{age: 30, height: 180, name: "Joe"}
# Access the value of name
joe_info.name #=> "Joe"
# Update the value of age
older_joe_info = %{ joe_info | age: 31 }
#=> %Person{age: 31, height: 180, name: "Joe"}
# The `try` block with the `rescue` keyword is used to handle exceptions
try do
  raise "some error"
rescue
  RuntimeError -> "rescued a runtime error"
  _error -> "this will rescue any error"
end
# All exceptions have a message
try do
  raise "some error"
rescue
  x in [RuntimeError] ->
    x.message
end

并发

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# Elixir relies on the actor model for concurrency. All we need to write
# concurrent programs in elixir are three primitives: spawning processes,
# sending messages and receiving messages.
# To start a new process we use the `spawn` function, which takes a function
# as argument.
f = fn -> 2 * 2 end #=> #Function<erl_eval.20.80484245>
spawn(f) #=> #PID<0.40.0>
# `spawn` returns a pid (process identifier), you can use this pid to send
# messages to the process. To do message passing we use the `send` operator.
# For all of this to be useful we need to be able to receive messages. This is
# achieved with the `receive` mechanism:
defmodule Geometry do
  def area_loop do
    receive do
      {:rectangle, w, h} ->
        IO.puts("Area = #{w * h}")
        area_loop()
      {:circle, r} ->
        IO.puts("Area = #{3.14 * r * r}")
        area_loop()
    end
  end
end
# Compile the module and create a process that evaluates `area_loop` in the shell
pid = spawn(fn -> Geometry.area_loop() end) #=> #PID<0.40.0>
# Send a message to `pid` that will match a pattern in the receive statement
send pid, {:rectangle, 2, 3}
#=> Area = 6
#   {:rectangle,2,3}
send pid, {:circle, 2}
#=> Area = 12.56000000000000049738
#   {:circle,2}
# The shell is also a process, you can use `self` to get the current pid
self() #=> #PID<0.27.0>