extract_ty (HsPredTy p) acc = extract_pred p acc
extract_ty (HsTyVar tv) acc = tv : acc
extract_ty (HsForAllTy Nothing cx ty) acc = extract_ctxt cx (extract_ty ty acc)
--- Generics
extract_ty (HsOpTy ty1 nam ty2) acc = extract_ty ty1 (extract_ty ty2 acc)
+extract_ty (HsParTy ty) acc = extract_ty ty acc
+-- Generics
extract_ty (HsNumTy num) acc = acc
extract_ty (HsKindSig ty k) acc = extract_ty ty acc
extract_ty (HsForAllTy (Just tvs) ctxt ty)