
  -spec erlang:function_exported(Module, Function, Arity) -> boolean()
                                    when
                                        Module :: module(),
                                        Function :: atom(),
                                        Arity :: arity().

  Returns true if the module Module is current and contains an
  exported function Function/Arity, or if there is a BIF (a
  built-in function implemented in C) with the specified name,
  otherwise returns false.
