arg :: TokenParser String
arg = token go P.<?> "arg"
  where go (Arg s) = Just s
        go _       = Nothing
arg :: TokenParser String
arg = token go P.<?> "arg"
  where go (Arg s) = Just s
        go _       = Nothing
arg = token go P.<?> "arg"
  where go (Arg s) = Just s
        go _       = Nothing