zip_blog_post_3.ex

defprotocol Add do
  def calculate(a, b)
end

# Now we can define implementations of it for the various kinds of
# data types we might get inside our collections that we are zipping.

defimpl Add, for: Integer do
  def calculate(a, b) when is_integer(b), do: a + b
end

defimpl Add, for: Decimal do
  def calculate(decimal, decimal_2 = %Decimal{}), do: Decimal.add(decimal, decimal_2)
end