Convert Enumeration to Integer

Hi,

I've read the VHDL FAQ 4.2.21 "How to Convert Between Enumeration and Integer Values". Anyway, I have questions to these function:

function slv2pec ( signal id : std_logic_vector(2 downto 0)) -- signal id : std_logic_vector(natural range )) return pattern_edge_comb_t is

begin -- Error: No feasible entries for infix operator "