decimal_prefix.ex

defmodule Decimal.Prefix do

  defmacro __using__(_args) do
    quote do
      import Decimal.Prefix, only: [decimal: 1]
    end
  end

  def overrides, do: ["+": 2, "-": 2, "*": 2, "/": 2]

  defmacro a + b do
    quote do: Decimal.add(unquote(a), unquote(b))
  end

  defmacro a - b do
    quote do: Decimal.add(unquote(a), unquote(b))
  end

  defmacro a * b do
    quote do: Decimal.mult(unquote(a), unquote(b))
  end

  defmacro a / b do
    quote do: Decimal.div(unquote(a), unquote(b))
  end

  defmacro decimal(code) do
    enclosed do
      quote do
        import Kernel, except: unquote(Decimal.Prefix.overrides())
        import Decimal.Prefix
        unquote(code)
      end
    end
  end

  defp enclosed(do: code), do: code
end