unless (isSynTyCon family) $
addErr (wrongKindOfFamily family)
- ; -- (1) kind check the right hand side of the type equation
+ ; -- (1) kind check the right-hand side of the type equation
; k_rhs <- kcCheckHsType (tcdSynRhs decl) resKind
-- (2) type check type equation
; t_typats <- mappM tcHsKindedType k_typats
; t_rhs <- tcHsKindedType k_rhs
- -- (3) construct representation tycon
+ ; -- (3) check that the right-hand side is a tau type
+ ; unless (isTauTy t_rhs) $
+ addErr (polyTyErr t_rhs)
+
+ -- (4) construct representation tycon
; rep_tc_name <- newFamInstTyConName tc_name loc
; tycon <- buildSynTyCon rep_tc_name t_tvs (SynonymTyCon t_rhs)
(Just (family, t_typats))
--
-- * Here we check that a type instance matches its kind signature, but we do
-- not check whether there is a pattern for each type index; the latter
--- check is only required for type functions.
+-- check is only required for type synonym instances.
--
kcIdxTyPats :: TyClDecl Name
-> ([LHsTyVarBndr Name] -> [LHsType Name] -> Kind -> TyCon -> TcM a)
| isAlgTyCon family = ptext SLIT("data type")
| otherwise = pprPanic "wrongKindOfFamily" (ppr family)
+polyTyErr ty
+ = hang (ptext SLIT("Illegal polymorphic type in type instance") <> colon) 4 $
+ ppr ty
+
emptyConDeclsErr tycon
= sep [quotes (ppr tycon) <+> ptext SLIT("has no constructors"),
nest 2 $ ptext SLIT("(-fglasgow-exts permits this)")]