bob.ex

defmodule Teenager do
  import String

  @reply_to_silence  "Fine. Be that way!"
  @reply_to_question "Sure."
  @reply_to_shout    "Woah, chill out!"
  @reply_to_other    "Whatever."

  def hey(message) do
    cond do
      silence?(message)  -> @reply_to_silence
      question?(message) -> @reply_to_question
      shout?(message)    -> @reply_to_shout
      other?(message)    -> @reply_to_other
    end
  end

  defp silence?(message), do: strip(message) == ""

  defp question?(message), do: ends_with?(message, "?")

  defp shout?(message), do: all_caps?(message)

  defp other?(_message), do: true

  defp all_caps?(message), do: message == upcase(message)
end