If you deal with legacy Erlang code, you may know the old erlang_decimal library. On Hex it's published as erlang_decimal, but it registers its OTP application (and its module) under the plain name decimal — the same name the modern Elixir decimal library uses for its own OTP application. Since a BEAM node can't run two applications with the same name, you can't depend on both at once.

fake_decimal solves this by providing the exact same API as the old decimal module, implemented on top of the modern Elixir Decimal library. Depend on fake_decimal (which pulls in the real decimal app) instead of erlang_decimal, and your legacy code can keep calling :decimal.add/2, :decimal.round/3, and so on without ever knowing it's talking to the new library underneath.

Add fake_decimal to your list of dependencies in mix.exs:

def deps do
  [
    {:fake_decimal, "~> 0.1.1"}
  ]
end

Documentation is available on HexDocs.

Property-based tests compare fake_decimal against a real instance of erlang_decimal, loaded in a separate node, to make sure the two behave identically.

See the @moduledoc in lib/fake_decimal.ex for the full API and the handful of intentional deviations from the original.