   end
 
   @doc """
-  Returns the alias for the given atom, `nil` otherwise.
+  Fetches the alias for the given atom.
+
+  Returns `{:ok, alias}` if the alias exists, `:error` 
+  otherwise.
 
   ## Examples
 

    do: Keyword.fetch(aliases, :"Elixir.#{atom}")

  @doc """
  Returns the macro alias for the given atom, `nil` otherwise.

  A macro alias is only used inside quoted expansion. See
  `fetch_alias/2` for a more general example.

      do: Keyword.fetch(aliases, :"Elixir.#{atom}")

  @doc """
  Returns the modules from which the given `{name, arity}` was
  imported.

  It returns a list of two element tuples in the shape of
  `{:function | :macro, module}`. The elements in the list
