decimal_range.ex

defmodule Decimal.Range do
  defstruct [:first, :last, :step]

  def new(first, last, step) do
    %__MODULE__{first: first, last: last, step: step}
  end

  def size(range) do
    range.last
    |> Decimal.sub(range.first)
    |> Decimal.div(range.step)
    |> Decimal.add(1)
    |> Decimal.round(0, :floor)
    |> Decimal.to_integer()
  end

  defimpl Enumerable do
    def reduce(_range, {:halt, acc}, _reducer) do
      {:halted, acc}
    end

    def reduce(range, {:suspend, acc}, reducer) do
      {:suspended, acc, fn next_acc -> reduce(range, next_acc, reducer) end}
    end

    def reduce(range, {:cont, acc}, reducer) do
      inside_positive_range? =
        Decimal.positive?(range.step) and not Decimal.gt?(range.first, range.last)

      inside_negative_range? =
        Decimal.negative?(range.step) and not Decimal.lt?(range.first, range.last)

      if inside_positive_range? or inside_negative_range? do
        next_range = %{range | first: Decimal.add(range.first, range.step)}
        next_acc = reducer.(range.first, acc)

        reduce(next_range, next_acc, reducer)
      else
        {:done, acc}
      end
    end

    def slice(range) do
      {:ok, @for.size(range), &Enum.to_list/1}
    end
  end
end

iex> range = Decimal.Range.new Decimal.from_float(0.1), Decimal.from_float(0.6), Decimal.from_float(0.2)
%Decimal.Range{first: Decimal.new("0.1"), last: Decimal.new("0.6"), step: Decimal.new("0.2")}

iex> Enum.to_list range
[Decimal.new("0.1"), Decimal.new("0.3"), Decimal.new("0.5")]

iex> Enum.random range
Decimal.new("0.5")

iex> Enum.reduce range, &Decimal.add/2
Decimal.new("0.9")