Elixir Fundamentals

Elixir Fundamentals for Elixir beginners

Transcript

1. Elixir Fundamentals
   (for Elixir beginners)
   Brian Zambrano
   Boulder Elixir Meetup
   December 6, 2016
   

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2. Me
   • Originally from SF Bay Area
   • Writing Python since 2001
   • Mostly backend systems +
   SAAS architecture +
   (micro)services
   • Plenty of Django
   • Plenty of horrible codebases
   • Looking for a better way
   

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3. What we'll cover
   • Elixir as a functional language
   • Data types
   • Pattern matching
   • Runtime/processes
   

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4. Why Elixir?
   • Scalability / concurrency
   • Distributed system / microservices usually requires tooling, systems and
   lots of management
   • Distributed programming built into the language via Erlang/BEAM
   • Performance
   • Many languages aren't that good at resource utilization: Python, Ruby,
   JavaScript/Node
   • Other more performant languages are a bit too low-level: C, Go, Rust
   • Functional
   • Immutable state means concurrency is easier
   • Immutable state means is harder to write big balls of mud
   

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5. Procedural or OO
   1 def calculate_taxes(username, year=2016):
   2 try:
   3 person = PeopleService(username)
   4 except PeopleService.NotFoudException:
   5 raise e
   6
   7 orders = OrdersService.get_orders_for_customer(person)
   8 if not orders:
   9 return
   10
   11 tax = calculate_sales_tax(orders, year)
   12
   13 return prepare_filing(tax)
   

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6. vs. Functional
   1 defmodule TaxService do
   2
   3 def calculate_taxes(username, year // 2016) do
   4 {:ok, person} = PeopleService(username)
   5
   6 person
   7 |> OrderService.for_customer
   8 |> calculate_taxes(year)
   9 |> prepare_filing
   10 end
   11
   12 end
   

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7. $ ls |
   > grep "\.exs" |
   > grep -v _test
   We already think
   functionally
   

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8. a = [1, 2, 3]
   func(a)
   # what is a?
   Removing mutation
   

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9. a = [1, 2, 3]
   func(a)
   a == [1, 2, 3]
   true # always
   In Elixir a won't change
   

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10. a = [1, 2, 3]
    a = func(a)
    # a has been re-bound
    # to a new list
    Rebinding isn't mutation
    

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11. Elixir types
    1, 100_000,
    0xDEADBEEF, 0b10111
    Integer
    1.0, 0.31415e1, 31415.0e-5 Float
    :ok, :is_binary?, :srsly! Atom
    1..10 Ranges
    ~r/[aeiou]/, ~r{[aeiou]} RegEx
    {:ok, file}, {:error, _} Tuple
    [1, 2, 3], ['a', 'b'] List
    %{ name: "bz", state: "CO" }
    %{ "CO" => "Colorado" }
    Map
    true, false, nil Truth
    <<1 :: size(4), 15 :: size(4)>> #
    0001 1111
    Binaries
    

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12. Elixir Strings
    • Single quoted
    • List of integers
    • iex represents this as a string if each char is
    printable
    • Double quoted
    • Sequence of UTF-8 bytes
    • Each byte is a binary
    

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13. Char lists
    iex(102)> [67, 97, 116]
    'Cat'
    iex(103)> is_list 'hello world'
    true
    iex(104)> List.to_tuple 'Cat'
    {67, 97, 116}
    iex(107)> 'CaӠ'
    [67, 97, 19971]
    

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14. Strings
    iex(128)> "C" == 'C'
    false
    iex(135)> [67]
    'C'
    iex(136)> "C" == << 67 :: size(8) >>
    true
    iex(138)> String.upcase("cat")
    "CAT"
    iex(146)> String.length("CaӠ")
    3
    iex(147)> byte_size("CaӠ")
    5
    

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15. Pattern
    matching
    

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16. Pattern matching vs
    variable assignment
    

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17. iex(5)> a = 1
    1
    iex(6)> 1 = 1
    1
    iex(7)> 1 = a
    1
    merely matching
    up the left and
    right side of "="
    

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18. 1 = a doesn't
    work in other
    languages
    >>> a = 1
    >>> 1 = a
    File "", line 1
    SyntaxError: can't assign to literal
    >>> 1 = 1
    File "", line 1
    SyntaxError: can't assign to literal
    >>>
    irb(main):001:0> a = 1
    => 1
    irb(main):002:0> 1 = a
    SyntaxError: (irb):2: syntax error,
    unexpected '=', expecting end-of-input
    1 = a
    ^
    from /usr/local/bin/irb:11:in `'
    irb(main):003:0> 1 = 1
    SyntaxError: (irb):3: syntax error,
    unexpected '=', expecting end-of-input
    1 = 1
    ^
    from /usr/local/bin/irb:11:in `'
    

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19. 1 = a cannot work in Elixir too!
    a must be defined before
    matching
    iex(1)> 1 = a
    ** (CompileError) iex:1: undefined function a/0
    iex(1)> a = 1
    1
    iex(2)> 1 = a
    1
    

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20. iex(8)> list = [1, 2, 3]
    [1, 2, 3]
    iex(9)> [a, 2, b] = list
    [1, 2, 3]
    iex(10)> a
    1
    iex(11)> b
    3
    Matching with lists
    

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21. iex(14)> list = [1, 2, 3]
    [1, 2, 3]
    iex(15)> [a, 1, b] = list
    ** (MatchError) no match of
    right hand side value: [1, 2, 3]
    Mis-matching with lists
    

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22. iex(14)> list = [1, 2, 3]
    [1, 2, 3]
    iex(15)> [1, _, b] = list
    [1, 2, 3]
    Ignoring during matching
    

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23. Pattern matching
    with Maps
    

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24. iex(2)> me = %{
    name: "Brian",
    age: 43
    }
    %{age: 43, name: "Brian"}
    iex(3)> %{name: aname} = me
    %{age: 43, name: "Brian"}
    iex(6)> aname
    "Brian"
    

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25. iex(7)> %{name: "Brian"} = me
    %{age: 43, name: "Brian"}
    iex(8)> %{name: "Joe"} = me
    ** (MatchError) no match of
    right hand side value: %{age:
    43, name: "Brian"}
    Mis-matching with maps
    

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26. Pattern matching
    in functions
    

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27. Matching based on
    function arguments
    1 defmodule Fib do
    2 def fib(1), do: 1
    3 def fib(2), do: 1
    4 def fib(n), do: fib(n-1) + fib(n-2)
    5 end
    

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28. Matching based on
    function arity
    1 defmodule Calculator do
    2
    3 def inc(n) do
    4 n + 1
    5 end
    6
    7 def inc(n, m) do
    8 n + m
    9 end
    10
    11 end
    

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29. Matching based on
    function arity
    iex(1)> Calculator.inc(5)
    6
    iex(2)> Calculator.inc(5, 5)
    10
    

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30. Processes and
    Supervisors
    

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31. Simple GenServer
    defmodule Calculator.Server do
    use GenServer
    # API
    def start_link do
    GenServer.start_link(__MODULE__, nil, name: :calculator)
    end
    def divide(n, m) do
    GenServer.call(:calculator, {:divide, n, m})
    end
    # end API
    

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32. Simple GenServer
    # Server callbacks
    def init(nil) do
    {:ok, nil}
    end
    def handle_call({:multiply, n, m}, _from, _state) do
    { :reply, n * m, nil }
    end
    end
    

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33. Running our Server
    iex(1)> Calculator.Server.start_link
    {:ok, #PID<0.119.0>}
    iex(2)> Calculator.Server.divide(10, 2)
    5.0
    iex(3)> Calculator.Server.divide(10, 0)
    ** (EXIT from #PID<0.117.0>) an exception was raised:
    
    State: nil
    nil
    iex(1)>
    iex(2)> Calculator.Server.divide(10, 2)
    ** (exit) exited in: GenServer.call(:calculator, {:divide, 10, 2}, 5000)
    ** (EXIT) no process
    (elixir) lib/gen_server.ex:596: GenServer.call/3
    

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34. Running with Supervisor
    1 defmodule Calculator.Supervisor do
    2 use Supervisor
    3
    4 def start_link do
    5 Supervisor.start_link(__MODULE__, [])
    6 end
    7
    8 def init(_) do
    9 children = [
    10 worker(Calculator.Server, [])
    11 ]
    12 supervise(children, strategy: :one_for_one)
    13 end
    14 end
    

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35. Running with Supervisor
    iex(1)> Calculator.Supervisor.start_link
    {:ok, #PID<0.108.0>}
    iex(2)> Calculator.divide(10, 2)
    5.0
    iex(3)> Calculator.divide(10, 0)
    ** (RuntimeError) Cannot divide by zero
    (calculator) lib/calculator.ex:6: Calculator.divide/2
    iex(3)> Calculator.divide(10, 2)
    5.0
    

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36. Resources
    Introduction to Elixir & Phoenix
    https://youtu.be/cKeJJldQRgI
    GenServer/Supervisor gists
    https://git.io/calculator
    https://git.io/supervisor
    Programming Elixir
    https://pragprog.com/book/elixir/programming-elixir
    Docs
    https://elixirschool.com
    http://elixir-lang.org/getting-started/introduction.html
    

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