opParens :: BinOp -> Exp -> Exp -> PP ()
opParens Sub a (BinOp Sub (Lit (LNum 0)) b) =
  opParens Add a b
opParens :: BinOp -> Exp -> Exp -> PP ()
opParens Sub a (BinOp Sub (Lit (LNum 0)) b) =
  opParens Add a b
opParens Sub a (BinOp Sub (Lit (LNum 0)) b) =
  opParens Add a b