         value -> value
       end
 
-  In the example above, we compare `thing` with each given
-  match clause and execute the first one that matches. If no
+  In the example above, we compare `thing` with each given match clause and
+  evaluate the expression corresponding to the first clause that matches. If no
   clause matches, an error is raised.
 
   Since Elixir variables can be assigned more than once, variables

  end

  @doc """
  Execute the first clause where the condition returns true,
  raises an error otherwise.

  ## Examples


  end

  @doc """
  Evaluates and returns the expression unless clause evaluates to true.
  Returns nil otherwise.
  See also `if`.

  ## Examples

      iex> unless(1, "Hello")
      nil
      iex> unless(false, "Hello")
      "Hello"

  """
  defmacro unless(clause, options) do
    do_clause   = Keyword.get(options, :do, nil)
