basic DFA simulation

dfa.exs

defmodule DFA do
  def accepts?(accept: accept_states, rules: rules, s: string) do
    string
    |> String.graphemes
    |> List.foldl(1, fn(char, state) -> next(state: state, char: char, rules: rules) end)
    |> member?(accept_states)
  end

  defp next(state: nil, char: _char, rules: _rules) do
    nil
  end
  defp next(state: state, char: char, rules: [{state, char, next_state}|_rest]) do
    next_state
  end
  defp next(state: state, char: char, rules: [_head|rest]) do
    next(state: state, char: char, rules: rest)
  end
  defp next(state: _state, char: _char, rules: []) do
    nil
  end

  defp member?(_state, []), do: false
  defp member?(state, [state|_rest]), do: true
  defp member?(state, [_head|rest]), do: member?(state, rest)
end