   end
 
   @doc """
-  Provides an unless macro that executes the expression
-  unless a value evaluates to true. Check `if` for examples
-  and documentation.
+  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)

        value -> value
      end

  In the example above, we compare `thing` with each given
  match clause and execute the first one that matches. If no
  clause matches, an error is raised.

  Since Elixir variables can be assigned more than once, variables

  end

  @doc """
  Evaluates the expression corresponding to the first clause that
  evaluates to true. Raises an error if all conditions evaluate to
  to falsy values (nil or false).

  ## Examples

