defmodule Queens do
  def solve(0, _m), do: [[]]
  def solve(n, m) do
    for done_queens <- solve(n-1, m),
        avail_pos <- (Enum.to_list(1..m) -- done_queens),
        safe_pos(avail_pos, done_queens, 1), 
      do: [avail_pos | done_queens]
  end

  defp safe_pos(_, [], _), do: true
  defp safe_pos(pos, [queen | queens], distance) do
    (pos != queen + distance) and 
    (pos != queen - distance) and 
    safe_pos(pos, queens, distance+1)
  end
end

:io.write Queens.solve(8,8)