let setcdr : 'a list -> 'a list -> unit = fun c v -> 
    let c = Obj.repr c in
    assert(Obj.is_block c) ;
    Obj.set_field c 1 (Obj.repr v)
;;

let lappend l1 l2 =
    let rec proc cell = function
        | [] ->
            setcdr cell l2
        | x :: l -> 
            let nxt = [ x ] in
                setcdr cell nxt ;
                proc nxt l
    in
    match l1 with
        | [] -> l2
        | x :: l ->
            let head = [ x ] in
                proc head l ;
                head
;;

let makelist c =
    let rec makelist_int c accum =
        if (c > 0) then
            makelist_int (c - 1) (lappend accum [ c ])
        else 
            (lappend accum [ c ])
in
    makelist_int c []
;;

let _ = makelist 5000;;