defmodule Hamming do
  @doc """
  Returns number of differences between two strands of DNA, known as the Hamming Distance.

  ## Examples

  iex> Hamming.hamming_distance('AAGTCATA', 'TAGCGATC')
  {:ok, 4}
  """
  @spec hamming_distance([char], [char]) :: non_neg_integer
  def hamming_distance(strand1, strand2) do
  end
end

defmodule Hamming do
  @doc """
  Returns number of differences between two strands of DNA, known as the Hamming Distance.

  ## Examples

  iex> Hamming.hamming_distance('AAGTCATA', 'TAGCGATC')
  {:ok, 4}
  """
  @spec hamming_distance([char], [char]) :: {:ok, non_neg_integer} | {:error, String.t()}
  def hamming_distance(strand1, strand2) do
  end
end

Fix the spec for Hamming problem.
Fix the spec for Hamming problem.

exercism/xelixir