Elixir Slides

slides.exs

add = fn(a, b) ->
  a + b
end

iex> add.(2, 3)
iex> 5

iex> list = [1, 2, 3]
iex> lenght(list)
iex> 3

iex> linked_list = [1 | [2 | [3 | []]]]
iex> lenght(linked_list)
iex> 3

iex> linked_list == list
iex> true

iex> tuple = {1, 2, 3}
iex> assert tuple_size(tuple) == 3
iex> assert elem(tuple, 1) == "2"

iex> {:ok, id} = create_some_process_id()

x = 1
assert (1 = x) == true
2 = x # MatchError!

type = :error
:error = type

{a, b, c} = {:ok, 1, "abc"}
assert a == :ok && b == 1 && c == "abc"

[w, c] = [1, 2] # w == 1 && c == 2

{:ok, id} = {:ok, 42} # id == 42
{:ok, id} = {:error, 42} # MatchError!

[head | tail] = [1, 2, 3]
assert head == 1 && tail == [2, 3]

def sort([]), do: []
def sort([elem]), do: [elem]
def sort([pivot | tail]) do
  {smallers, largers} = partition(pivot, tail, [], [])
  sort(smallers) ++ [pivot] ++ sort(largers)
end

sort([2, 3, 1]) # will match the 3rd
sort([1, 2]) # will match the 3rd
sort([3]) # will match the 2nd
sort([]) # will match the first and return the sorted list

sort([1]) ++ [2] ++ sort([3]) # [1, 2, 3]

map = %{:age => 22, "name" => "John"}
assert map[:age] == 22 # or map.age == 22
assert map["name"] == "John" # or map.name == "John"

new_map = %{map | :age => 23}
assert map.age == 23
assert map.name == "John"

calculator_fn = fn ->
  receive do
    {:sum, [a, b]} -> 
      sum = a + b
      IO.puts("Sum: #{sum}")
  end
end

calculator_id = spawn(calculator_fn)
send(calculator_id, {:sum, [1, 2]}) # prints Sum: 3

defmodule Calculator do
  def start do
    receive do
      {:sum, [a, b]} -> 
        sum = a + b
        IO.puts("Sum: #{sum}")
    end
    
    start()
  end
end

calculator_id = spawn(Calculator, :start, [])
send(calculator_id, {:sum, [1, 2]}) # prints Sum: 3
send(calculator_id, {:sum, [1, 2]}) # prints Sum: 3 (yay)

defmodule MyList do
  def start(list) do
    new_list = receive do
      {:prepend, elem} -> [elem | list]
      :print -> IO.inspect(list)
    end
    
    start(new_list)
  end
end

list_id = spawn(MyList, :start, [[]])
send(list_id, {:prepend, 1})
send(list_id, {:prepend, 5})
send(list_id, :print) # [5, 1]

iex> self()
#PID<0.84.0>

iex> spawn fn -> raise "oops" end
#PID<0.296.0>

16:19:08.954 [error] Process #PID<0.296.0> raised an exception
** (RuntimeError) oops
    (stdlib) erl_eval.erl:668: :erl_eval.do_apply/6

iex> self()
#PID<0.84.0>

iex> spawn_link fn -> raise "oops" end

16:22:04.485 [error] Process #PID<0.306.0> raised an exception
** (RuntimeError) oops
    (stdlib) erl_eval.erl:668: :erl_eval.do_apply/6
** (EXIT from #PID<0.84.0>) shell process exited with reason: an exception was raised:
    ** (RuntimeError) oops
        (stdlib) erl_eval.erl:668: :erl_eval.do_apply/6

iex> self()
#PID<0.307.0>

defmodule Calculator do
  @spec add(number, number) :: number
  def add(x, y), do: x + y
end

defmodule Parser do
  @callback parse(String.t) :: {:ok, term} | {:error, String.t}
  @callback extensions() :: [String.t]
end

defmodule JSONParser do
  @behaviour Parser

  def parse(str), do: {:ok, "some json " <> str} # ... parse JSON
  def extensions, do: ["json"]
end