Elixir didn’t introduce a protocol, but it already kinda standardized compare/2 to return :lt | :eq | :gt for passing a module to sorting functions of Enum with elixir 1.10: Enum — Elixir v1.14.0

Decimal had to do a mayor version update for the breaking change moving from -1 | 0 | 1 to :lt | :eq | :gt. It seems like Timex didn’t do so.

defprotocol Comparable do
  def compare(a, b)
end

defimpl Comparable,
  for: [Tuple, Atom, List, BitString, Integer, Float, Function, PID, Map, Port, Reference] do
  def compare(a, b) when a < b, do: :lt
  def compare(a, b) when a == b, do: :eq
  def compare(a, b) when a > b, do: :gt
end

Usage:

iex(1)> Comparable.compare(1, 2)
:lt
iex(2)> Comparable.compare("z", "a")
:gt
iex(3)> Comparable.compare([{:foo, "bar"}], foo: "bar")
:eq

No, only indirectly here: myers

Also Date and Time compare return those: Date — Elixir v1.14.0

Or: defdelegate compare(a, b), to: @for

Also Version.compare/2 and Logger.compare_levels/2.

I think such atoms are not needed for types that can be compared directly using term order.