sublist.ml

let rec sublists a = match a with
    [] -> [[]]
    |first::rest -> let b = sublists rest in
        let c = List.map (fun g -> first::g) b in
        c @ b;;

(*
val sublists : 'a list -> 'a list list = <fun>
# let a = [1;2;3];;
val a : int list = [1; 2; 3]
# sublists a;;
- : int list list = [[1; 2; 3]; [1; 2]; [1; 3]; [1]; [2; 3]; [2]; [3]; []]
*)