Elixir Weekday struct with Range.Iterator implementation

weekday.ex

defmodule Weekday do
  defstruct name: nil, number: nil

  def monday, do: %Weekday{name: "Monday", number: 1}
  def tuesday, do: %Weekday{name: "Tuesday", number: 2}
  def wednesday, do: %Weekday{name: "Wednesday", number: 3}
  def thursday, do: %Weekday{name: "Thursday", number: 4}
  def friday, do: %Weekday{name: "Friday", number: 5}
  def saturday, do: %Weekday{name: "Saturday", number: 6}
  def sunday, do: %Weekday{name: "Sunday", number: 7}
end

defimpl Range.Iterator, for: Weekday do
  def next(_first, _range) do
    fn weekday ->
      case weekday.number do
        1 -> Weekday.tuesday
        2 -> Weekday.wednesday
        3 -> Weekday.thursday
        4 -> Weekday.friday
        5 -> Weekday.saturday
        6 -> Weekday.sunday
        7 -> Weekday.monday
      end
    end
  end

  def count(_, first..last) do
    if first.number <= last.number do
      last.number + 1 - first.number
    else
      last.number + 8 - first.number
    end
  end
end