type plate = int * int * int ;;
type game_statu =
   Non_term of int
  |P1 of int
  |P2 of int
  |Match_nul of int;;

let init a:plate =(0,a,a);;

let display a:plate =
  let (b,c,d)=
  match a with
     (-1,_,_) -> ("x"," "," ")
    |(_,_,_) -> (" ","X","X")
in print_string "b^c^d";;



Warning Y: unused variable d.
Characters 32-33:
    let (b,c,d)=
           ^
Warning Y: unused variable c.
Characters 30-31:
    let (b,c,d)=
         ^
Warning Y: unused variable b.
Characters 117-137:
  in print_string "b^c^d";;
     ^^^^^^^^^^^^^^^^^^^^
Error: This expression has type unit but is here used with type
         plate = int * int * int