How to typespec a float range in Elixir?

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Exactly what I did, and what a funny coincidence that I just had to code something super similar in the last two days:

  @type double :: float()

  @double_min -1.7976931348623157e308
  @double_max 1.7976931348623157e308

  defguard is_double(x) when is_float(x) and x >= @double_min and x <= @double_max

  @spec do_stuff(double()) :: nil
  def do_stuff(x) when is_double(x) do
    dec = Decimal.from_float(x)
    if Decimal.compare(dec, @decimal_double_min) != :lt and
         Decimal.compare(dec, @decimal_double_max) != :gt do
      # the float is in range, let's do stuff!
    else
      # out of bounds, report error.
    end

    # do something else and return.
    nil
  end

As you said, it’s definitely better than nothing. Basically everything except the typespec itself is covered. I am nervous about using >= and <= in the guard but my tests have shown that the comparisons are stable for these boundary values .

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