defmodule Demo do
  @spec foo(integer(), float()) :: float()
  @spec foo(float(), integer()) :: float()
  def foo(a, b) when is_integer(a) and is_float(b) do
    do_foo_if(a, b)
  end

  def foo(a, b) when is_float(a) and is_integer(b) do
    do_foo_fi(a, b)
  end

  @spec do_foo_if(integer(), float()) :: float()
  defp do_foo_if(a, b) do
    a + b
  end

  @spec do_foo_fi(float(), integer()) :: float()
  defp do_foo_fi(a, b) do
    a + b
  end
end

<...>
  def bar() do
    foo(2.0, 2.0)
  end
<...>

The contract 'Elixir.Demo':foo(integer(),float()) -> float()
    ; (float(),integer()) -> float() cannot be right because the inferred return for foo(2.0,2.0) on line 4 is float()

  def bar() do
    foo(2.0, 2)
  end