create ++ operator in VHDL

I would like to have a new C++ style operator for the STD_LOGIC_VECTOR type. So far I managed to create and use the following function:

FUNCTION PLUS_ONE ( a : STD_LOGIC_VECTOR) RETURN STD_LOGIC_VECTOR is 
BEGIN
    RETURN std_logic_vector( unsigned( a ) + 1);
END FUNCTION;

now if i create this:

FUNCTION "++" ( a : STD_LOGIC_VECTOR) RETURN      STD_LOGIC_VECTOR is 
BEGIN
    RETURN std_logic_vector( unsigned( a ) + 1);
END FUNCTION;

ISE throws the following error:

"++" is not a predefined operator.

Now the question is, is it possible to create new operators in VHDL an I am missing something