let cCAMLtoTKbitmap : bitmap -> tkArgs = function
| `File s -> TkToken ("@" ^ s)
| `Predefined s -> TkToken s
let cTKtoCAMLbitmap s =
if String.get s 0 = '@'
then `File (String.sub s ~pos:1 ~len:(String.length s - 1))
else `Predefined s