-- ToDo
-- binOp = do
--   spaces
--   char '+'
--   spaces
--   lhs <- expr
--   spaces
--   rhs <- expr
--   spaces
--   return $ BinOp Plus lhs rhs
-- binOp = spaces *> char '+' *> return (BinOp Plus) <* spaces <*> expr *> spaces <*> expr

abs' :: Parser Term
abs' = parserZero
abs' :: Parser Term
abs' = parserZero
abs' = parserZero