duelist.ex

# Day List

## Module

```elixir
defmodule DayList do
  @days [:sun, :mon, :tues, :wed, :thurs, :fri, :sat]

  @spec build_list(first :: atom(), last :: atom()) :: list() | {:error, :invalid_day}
  def build_list(first, last) when first in @days and last in @days do
    @days
    |> Stream.cycle()
    |> Stream.drop_while(&(&1 != first))
    |> Stream.take_while(&(&1 != last))
    |> Enum.to_list()
    |> Kernel.++([last])
  end

  def build_list(_, _), do: {:error, :invalid_day}
end
```

```output
{:module, DayList, <<70, 79, 82, 49, 0, 0, 9, ...>>, {:build_list, 2}}
```

```elixir
DayList.build_list(:sat, :fri)
```

```output
[:sat, :sun, :mon, :tues, :wed, :thurs, :fri]
```