The function you’re looking for is this one: Calendar.strftime/3

That will let you pass in the date and then a format string in which you can specify things like the full name of the month, date, etc.

Nah The below is the real overusing of Elixir killer features:

defmodule DayEnding do
  Enum.each(1..31, fn
    day when div(day, 10) == 1 -> def ending(unquote(day)), do: "th"
    day when rem(day, 10) == 1 -> def ending(unquote(day)), do: "st"
    day when rem(day, 10) == 2 -> def ending(unquote(day)), do: "nd"
    day when rem(day, 10) == 3 -> def ending(unquote(day)), do: "rd"
    day -> def ending(unquote(day)), do: "th"
  end)
end

It could be implemented somewhere in Cldr.Calendars or Cldr.Numbers. If it isn’t, or if you’re not willing to add an extra dependency, writing your own implementation is straightforward:

def ending(day) when day in [1, 21, 31], do: "st"
def ending(day) when day in [2, 22], do: "nd"
def ending(day) when day in [3, 23], do: "rd"
def ending(_), do: "th"