extract_ctxt ctxt acc = foldr extract_pred acc ctxt
-extract_pred (HsPClass cls tys) acc = foldr extract_ty (cls : acc) tys
-extract_pred (HsPIParam n ty) acc = extract_ty ty acc
+extract_pred (HsClassP cls tys) acc = foldr extract_ty (cls : acc) tys
+extract_pred (HsIParam n ty) acc = extract_ty ty acc
extract_tys tys = foldr extract_ty [] tys