Paramath.ex

defmodule Paramath do
  def fast_fac(n, procn, pid) do
    recver = spawn_link(fn -> recv(procn, 1, pid) end)
    mkfac(n, div(n, procn) + rem(n, procn), recver)
  end
  defp mkfac(n, intval, out) do
    cond do
      n > intval ->
        spawn_link(fn -> calc_range(n, n - intval, 1, out) end)
        mkfac(n - intval, intval, out)
      n > 1 ->
        spawn_link(fn -> calc_range(n, 1, 1, out) end)
        {}
      :true -> {}
    end
  end
  defp calc_range(from, downto, res, out) do
    if from > downto do
      calc_range(from - 1, downto, res * from, out)
    else
      send(out, {:partial, res})
    end
  end
  defp recv(i, res, out) do
    if i > 0 do
      receive do
        {:partial, n} -> recv(i - 1, res * n, out)
      end
    else
      send(out, {:factorial, res})
    end
  end
end