def add_return_type(self, return_type):
        """Add *return_type* to the list of inferred return-types.
        If there are too many, raise `TypingError`.
        """
        # The maximum limit is picked arbitrarily.
        # Don't think that this needs to be user configurable.
        RETTY_LIMIT = 16
        self._inferred_retty.add(return_type)
        if len(self._inferred_retty) >= RETTY_LIMIT:
            m = "Return type of recursive function does not converge"
            raise errors.TypingError(m)
Add *return_type* to the list of inferred return-types.
        If there are too many, raise `TypingError`.
        
numba/core/typing/context.py