mread' :: [Expr] -> Opti [Name]
mread' exprs = do
  a <- mapM mread exprs
  return $ concat a
mread' :: [Expr] -> Opti [Name]
mread' exprs = do
  a <- mapM mread exprs
  return $ concat a
mread' exprs = do
  a <- mapM mread exprs
  return $ concat a