map_extras.ex

defmodule MapExtras do
  def take_strict!(map, keys) do
    existing_keys = Map.keys(map)

    case Enum.all?(keys, fn(k) -> Enum.member?(existing_keys, k) end) do
      true -> Map.take(map, keys)
      false -> raise "One or more of the keys passed does not exist in the map"
    end
  end
  
  def take_strict(map, keys) do
    existing_keys = Map.keys(map)

    case Enum.all?(keys, fn(k) -> Enum.member?(existing_keys, k) end) do
      true -> {:ok, Map.take(map, keys)}
      false -> {:error, "One or more of the keys passed does not exist in the map"}
    end
  end
end