anchor.diff:      boolean telling whether the map was modified.
       
       If the open is an implicit open (as indicated by the flag),
  -    make sure that we don't overshadow any existing entry *)
  +    and doing so shadows an existing entry, warn! *)
   let enter_namespace
     (original_map: files_for_module_name)
     (working_map: files_for_module_name)
  
positive.code:     match sopt with
      | None -> "<None>"
      | Some s -> s in
    smap_iter m (fun k (intf, impl) -> BU.print3 "%s:(%s, %s)\n" k (str_opt_to_string intf) (str_opt_to_string impl));
    BU.print_string "}\n"
  
  type color = | White | Gray | Black
  
negative.code:   | VerifyUserList
    | VerifyFigureItOut
  
  type intf_and_impl = option<string> * option<string>
  
  type files_for_module_name = smap<intf_and_impl>
  
  let intf_and_impl_to_string ii =
    match ii with
    | None, None -> "<None>, <None>"
    | Some intf, None -> intf
    | None, Some impl -> impl
    | Some intf, Some impl -> intf ^ ", " ^ impl
  
  
  let files_for_module_name_to_string (m:files_for_module_name) =
    BU.print_string "Printing the file system map {\n";
  