Inferring ROM module

Thanks everyone for helping me. I managed to solve the problem by adding clock to the module. Here's the final code :

module LUT256DFF (
Clk,
ADDR,    // Address input
DataOut, // Data output
RE,      // Read Enable 
CE       // Chip Enable
) /* synthesis romstyle = "M4K" */;  
input Clk;
input  ADDR;
output  DataOut; 
input RE,CE; 
           
(* romstyle = "M4K" *) reg  mem  ;  
reg  DataOut;
always @ (posedge Clk)
begin      
  if (CE && RE)
    DataOut <= mem;
end
initial begin
  $readmemb("sine_value.list", mem);  // sine_value is pre-calcualted external memory file
end
endmodule