Recursive combinations with subsets

combinations.exs

defmodule Combination do
  def combine([]) do
    []
  end

  def combine([head | tail]) do
    tail_combinations = combine(tail)
    merged_combinations = Enum.map(
      [[]] ++ tail_combinations,
      fn c -> c ++ [head] end
    )
    tail_combinations ++ merged_combinations
  end
end

input = ["a", "b", "c"]
Combination.combine(input)
|> IO.inspect(limit: :infinity)