I wrote the function used to decompose a Boolean function, the problem is that the compilation I get this : "Warning 5: this function application is partial, maybe some arguments are missing." How can I solve this problem? I've set wrong the patter matching or I can not run this operation with pattern matching

The code is the following:

         let rec decomposition state_init state prec formula =        
            match formula with        
            And form -> (fun () -> 
                    let f1 = List.hd form in
                    let f2 = And(List.tl form )in                      

                    let new_state = Forms (state_init,f1) in

                    decomposition state_init new_state state f1;            

                    decomposition state_init new_state state f2;

                    Hashtbl.add graph new_state (("",false,state :: []) , []) ;

                    let x = Hashtbl.find graph state in
                    let succ = state :: snd x in
                    let (desc,last,ptrs) = fst x in

                    Hashtbl.replace graph state ( ("And-node",last,ptrs) , succ))