OS.FileSys.readDir conformance

[ratmice]

Noticed a minor issue in the implementation of OS.FileSys.readDir,
According to sml-family

readDir filters out the names corresponding to the current and parent arcs.

I had not quite figured out how to generate the whole .ans file, etc

(* Result: FAIL *)
(* Test OS.FileSys.readDir, should return false. *)
fun hasParentOrCurrentArc() =
  let val cwd = OS.FileSys.openDir(OS.Path.currentArc)
      fun hasParentOrCurrentArc(d, flag) =
          let val entry = OS.FileSys.readDir(d)
              fun check(entry) = 
                String.compare(entry, OS.Path.parentArc) = General.EQUAL
                orelse String.compare(entry, OS.Path.currentArc) = General.EQUAL
              fun ent (SOME entry, false) = hasParentOrCurrentArc(d, check(entry))
                | ent (SOME entry, true) = true
                | ent (NONE, flag) = flag 
           in ent (entry, flag)
          end
   in hasParentOrCurrentArc(cwd, false)
  end
val a = hasParentOrCurrentArc();