Getting around stupid constraints

fixrange.sml

(* 03:40 < Oejet> How would you implement f n = [1, ..., n], using only map, or 
                 foldl?
*)

fun range n = foldl (op ::) [] (
    (fn fix => fix (fn f => fn n => case n of 0 => [] | n => n::f (n-1)))
    (
        fn f =>
            (fn cell =>
            (fn f' => (fn () => f')(cell := SOME f')
            )(f (fn x => valOf (!cell) x))
            )(ref NONE)
    ) n
    )