Quick-and-dirty guess the number implementation in Elixir

guess.exs

defmodule Guess do
  @moduledoc """
  Number guessing game module.
  """

  @doc """
  Guess the supplied `secret` by recursively bisecting the specified number `range`.
  """
  def guess(secret, range = lo..hi) when lo <= hi do
    _guess(_mid(range), secret, range)
  end

  @doc """
  Guess the supplied `secret` by recursively bisecting the specified number `range`.
  """
  def guess(secret, lo..hi) when lo > hi do
    range = hi..lo
    _guess(_mid(range), secret, range)
  end

  # Correct guess.
  defp _guess(current_guess, current_guess, _) do
    IO.puts("Guessed the secret! It was #{current_guess}.")

    current_guess
  end

  # Incorrect guess, keep trying.
  defp _guess(current_guess, secret, lo..hi) do
    mid = _mid(lo..hi)

    IO.puts("Current = #{current_guess}, Secret = #{secret}, Lo..Hi = #{lo}..#{hi}")

    {next_guess, next_range} = cond do
      secret <= mid -> {mid - lo, lo..mid}
      secret > mid  -> {hi - mid, mid..hi}
    end

    _guess(next_guess, secret, next_range)
  end

  # Get the middle value of the specified number range.
  defp _mid(lo..hi) do
    div(hi - lo, 2)
  end
end