sexpr2xml' ::  Sexpr ->  Maybe Element
sexpr2xml' (List (Atom name:List ats:els)) = do
    attrs <- mapM readAts ats
    elems <- mapM sexpr2xml' els
    return $ Elem name attrs elems
sexpr2xml' _ = Nothing

readAts :: Sexpr -> Maybe Attribute
readAts (List (Atom name:Atom val:[])) = Just $ Attr name val
readAts _ = Nothing