Jeweller-Tsai

def next %Date{year: y, month: m, day: d} do
  case Date.new(y, m, d + 1) do
    {:ok, nd} -> nd
    {:error, _} ->
      case Date.new(y, m + 1, 1) do
        {:ok, nd} -> nd
        {:error, _} ->
          {:ok, nd} = Date.new(y + 1, 1, 1)
          nd
      end

Jeweller-Tsai

defmodule ExclusiveDateRange do

  defstruct first: nil, last: nil

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

  defimpl Enumerable, for: ExclusiveDateRange do
    def reduce _dr, {:halt, acc}, _fun do

Jeweller-Tsai

defmodule DateRange do

  defstruct first: nil, last: nil, first_gregorian_days: nil, last_greogorian_days: nil

  defmodule Operator do
    def first <~> last do
      DateRange.new first, last
    end
  end

Jeweller-Tsai

defmodule Node do
  defstruct value: "", children: []
end