Arithmetic protocol for Elixir

arithmetic_protocol.ex

defprotocol Arithmetic.Add do
  @moduledoc """
  The Arithmetic.Add protocol is responsible for adding items.
  
  The only function required to be implemented is
  `__add__` which does the addition.
  """
  def __add__(left, right)
end

defimpl Arithmetic.Add, for: Decimal do
  alias Decimal, as: D
  
  def __add__(left, right) when is_decimal(right) do
    D.add(left, right)
  end

  def __add__(left, right) do
    D.add(left, D.new(right))
  end
end

defimpl Arithmetic.Add, for: Integer do
  def __add__(left, right) do
    :erlang.+(left, right)
  end
end

defimpl Arithmetic.Add, for: Float do
  def __add__(left, right) do
    :erlang.+(left, right)
  end
end


## In Kernel.ex, line 822
@spec (number + number) :: number
def left + right do
  Arithmetic.Add.__add__(left, right)
end

## Arithmetic.Add in action
alias Decimal, as: D
d1 = D.new(23.6)
d2 = D.new(9.54)
d1 + d2 # ==>  Arithmetic.Add.__add__(d1, d2)