Presence protocol for Elixir

presence.ex

defprotocol Presence do
  @doc "Determines whether the value is present and truthy"
  def present?(data)
end

defimpl Presence, for: Atom do
  def present?(false), do: false
  def present?(nil),   do: false
  def present?(_),     do: true
end

defimpl Presence, for: [Integer, Float] do
  def present?(_), do: true
end

defimpl Presence, for: BitString do
  def present?(""),     do: false
  def present?(string), do: String.trim(string) != ""
end

defimpl Presence, for: URI do
  def present?(%URI{}), do: false
  def present?(_),      do: true
end

defimpl Presence, for: [List, Keyword] do
  def present?([]), do: false
  def present?(_),  do: true
end

defimpl Presence, for: Tuple do
  def present?({}), do: false
  def present?(_),  do: true
end