Naive Tree implementation in Elixir

tree.ex

defmodule Tree do
  @moduledoc false

  def create_job(reducer_pid, func) do
    receive do
      job_input -> send(reducer_pid, func.(job_input))
    end
  end

  def mappers(_, _, [], job_pids), do: job_pids

  def mappers(reducer_pid, func, [job_input | rest], job_pids) do
    pid = spawn_link(Tree, :create_job, [reducer_pid, func])
    send(pid, job_input)
    mappers(reducer_pid, func, rest, [pid | job_pids])
  end

  def reducer(from_pid, job_count, acc) when job_count == length(acc), do: send(from_pid, acc)

  def reducer(from_pid, job_count, acc) do
    receive do
      result -> reducer(from_pid, job_count, [result | acc])
    end
  end


  def map_reduce(from_pid, func, inputs) do
    reducer_pid = spawn_link(Tree, :reducer, [from_pid, Enum.count(inputs), []])
    _ = mappers(reducer_pid, func, inputs, [])
  end

  def contents_of(dir_path) do
    {:ok, dir_content} = File.ls(dir_path)
    {directories, files} = Enum.split_with(dir_content, &File.dir?/1)
    sub_dir_paths = Enum.map(directories, &(Path.join(dir_path, &1)))
    [dir_path: dir_path, files: files, sub_directories: tree(sub_dir_paths)]
  end



  def tree(directories) do
    task = Task.async(fn ->
      map_reduce(self(), &contents_of/1, directories)
      receive do
        res -> res
      end
    end)
    Task.await(task)
  end

  def main(args) do
    IO.puts inspect(tree(args), pretty: true)
  end
end