Chapter 6

Mix.install([
  {:json, "~> 1.4"}
])

Exercise: ModulesAndFunctions-1 & 3

defmodule Times do
  def double(n), do: n * 2
  def triple(n), do: n * 3
  def quadruple(n), do: n * 4
end

Exercise: ModulesAndFunctions-4

defmodule Sum do
  def from_1_to(1), do: 1
  def from_1_to(n) when is_integer(n) and n > 1, do: n + from_1_to(n - 1)
end

5050 = Sum.from_1_to(100)

Exercise: ModulesAndFunctions-5

defmodule Math do
  def gcd(x, 0) when is_integer(x) and x >= 0, do: x
  def gcd(x, y) when is_integer(x) and x >= 0 and is_integer(y) and y >= 0, do: gcd(y, rem(x, y))
end

6 = Math.gcd(54, 24)

Exercise: ModulesAndFunctions-6

defmodule Chop do
  def guess(actual, range = low..high) do
    guess = div(low + high, 2)
    IO.puts("Is it #{guess}")
    guess(actual, range, guess)
  end

  defp guess(actual, low.._, guess) when guess > actual, do: guess(actual, low..(guess - 1))
  defp guess(actual, _..high, guess) when guess < actual, do: guess(actual, (guess + 1)..high)
  defp guess(_, _, guess), do: guess
end

Chop.guess(273, 1..1000)

Exercise: ModulesAndFunctions-7

# Convert a float to a string with two decimal digits. (Erlang)
:io_lib.format("~.2f", [3.1415]) |> IO.puts()

# Get the value of an operating-system environment variable. (Elixir)
System.get_env("ELIXIR_EDITOR") |> IO.puts()

# Return the extension component of a file name (so return .exs if given "dave/test.exs"). (Elixir)
Path.extname("dave/test.exs") |> IO.puts()

# Return the process’s current working directory. (Elixir)
File.cwd!() |> IO.puts()

# Convert a string containing JSON into Elixir data structures.
JSON.decode!(~s({"key":"this will be a value"})) |> IO.inspect()

# Execute a command in your operating system’s shell.
System.cmd("say", ["Hello world"])
:os.cmd('say Hello world')