decimal_math.exs

Mix.install([:decimal])

defmodule DecimalMath do
  alias Decimal, as: D
  import Decimal

  defmacro __using__(_opts) do
    quote do
      import Kernel, except: [*: 2, /: 2, +: 2, -: 2]
      import DecimalMath
    end
  end

  def left + right,
    do: D.add(dec(left), dec(right))

  def left - right,
    do: D.sub(dec(left), dec(right))

  def left * right,
    do: D.mult(dec(left), dec(right))

  def left / right,
    do: D.div(dec(left), dec(right))

  defp dec(value) when is_decimal(value), do: value
  defp dec(value) when is_float(value), do: Decimal.from_float(value)
  defp dec(value) when is_number(value), do: Decimal.new(value)
  defp dec(value) when is_binary(value), do: Decimal.new(value)
end

defmodule Test do
  use DecimalMath

  def run do
    IO.inspect(10 * 12 / 365 * 5, label: "10 * 12 / 365 * 5")
    IO.inspect(10 * 12 / 365 * 5.0, label: "10 * 12 / 365 * 5.0")
    IO.inspect(10 * "12.0" / "365" * 5.0, label: ~s[10 * "12.0" / "365" * 5.0])
    :tiddies
  end
end