let rec rev_append x y =
    match x with
        [] -> y
        | h :: t -> rev_append t (h :: y)
;;

let rev x =
    let rec rev_int x accum =
        match x with
            [] -> accum
            | h :: t -> rev_int t (h :: accum)
    in
        rev_int x []
;;

let lappend x y = 
    rev_append (rev x) ( [ y ] ) ;;

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;;