opParens Sub a (Lit (LNum n)) | n < 0 =
  opParens Add a (Lit (LNum (-n)))
opParens Sub a (Lit (LNum n)) | n < 0 =
  opParens Add a (Lit (LNum (-n)))
opParens Sub a (Lit (LNum n)) | n < 0 =
  opParens Add a (Lit (LNum (-n)))