; rep_tc_name <- newFamInstTyConName tc_name (srcSpanStart loc)
; tycon <- fixM (\ tycon -> do
- { data_cons <- mappM (addLocM (tcConDecl unbox_strict new_or_data
- tycon t_tvs))
+ { data_cons <- mappM (addLocM (tcConDecl unbox_strict tycon t_tvs))
k_cons
; tc_rhs <-
case new_or_data of
(newtypeConError tc_name (length cons))
; tycon <- fixM (\ tycon -> do
- { data_cons <- mappM (addLocM (tcConDecl unbox_strict new_or_data
- tycon final_tvs))
+ { data_cons <- mappM (addLocM (tcConDecl unbox_strict tycon final_tvs))
cons
; tc_rhs <-
if null cons && is_boot -- In a hs-boot file, empty cons means
-----------------------------------
tcConDecl :: Bool -- True <=> -funbox-strict_fields
- -> NewOrData
-> TyCon -> [TyVar]
-> ConDecl Name
-> TcM DataCon
-tcConDecl unbox_strict NewType tycon tc_tvs -- Newtypes
- (ConDecl name _ tvs ex_ctxt details res_ty _)
- = tcTyVarBndrs tvs $ \ tvs' -> do
- do { (univ_tvs, ex_tvs, eq_preds, data_tc) <- tcResultType tycon tc_tvs tvs' res_ty
-
- -- Check that a newtype has no existential stuff
- ; checkTc (null ex_tvs && null (unLoc ex_ctxt)) (newtypeExError name)
-
- ; let tc_datacon field_lbls arg_ty
- = do { arg_ty' <- tcHsKindedType arg_ty -- No bang on newtype
- ; buildDataCon (unLoc name) False {- Prefix -}
- [NotMarkedStrict]
- (map unLoc field_lbls)
- univ_tvs [] -- No existentials
- [] [] -- No equalities, predicates
- [arg_ty']
- data_tc }
-
- ; case details of
- PrefixCon [arg_ty] -> tc_datacon [] arg_ty
- RecCon [HsRecField field_lbl arg_ty _] -> tc_datacon [field_lbl] arg_ty
- other ->
- failWithTc (newtypeFieldErr name (length (hsConArgs details)))
- -- Check that the constructor has exactly one field
- }
-
-tcConDecl unbox_strict DataType tycon tc_tvs -- Data types
+tcConDecl unbox_strict tycon tc_tvs -- Data types
(ConDecl name _ tvs ctxt details res_ty _)
= tcTyVarBndrs tvs $ \ tvs' -> do
{ ctxt' <- tcHsKindedContext ctxt
= setSrcSpan (srcLocSpan (getSrcLoc con)) $
addErrCtxt (dataConCtxt con) $
do { checkTc (dataConTyCon con == tc) (badDataConTyCon con)
- ; checkValidType ctxt (dataConUserType con) }
+ ; checkValidType ctxt (dataConUserType con)
+ ; ifM (isNewTyCon tc) (checkNewDataCon con)
+ }
where
ctxt = ConArgCtxt (dataConName con)
-------------------------------
+checkNewDataCon :: DataCon -> TcM ()
+-- Checks for the data constructor of a newtype
+checkNewDataCon con
+ = do { checkTc (isSingleton arg_tys) (newtypeFieldErr con (length arg_tys))
+ -- One argument
+ ; checkTc (null eq_spec) (newtypePredError con)
+ -- Return type is (T a b c)
+ ; checkTc (null ex_tvs && null theta) (newtypeExError con)
+ -- No existentials
+ }
+ where
+ (univ_tvs, ex_tvs, eq_spec, theta, arg_tys) = dataConFullSig con
+
+-------------------------------
checkValidClass :: Class -> TcM ()
checkValidClass cls
= do { -- CHECK ARITY 1 FOR HASKELL 1.4
= sep [ptext SLIT("A newtype constructor cannot have an existential context,"),
nest 2 $ ptext SLIT("but") <+> quotes (ppr con) <+> ptext SLIT("does")]
+newtypePredError con
+ = sep [ptext SLIT("A newtype constructor must have a return type of form T a1 ... an"),
+ nest 2 $ ptext SLIT("but") <+> quotes (ppr con) <+> ptext SLIT("does not")]
+
newtypeFieldErr con_name n_flds
= sep [ptext SLIT("The constructor of a newtype must have exactly one field"),
nest 2 $ ptext SLIT("but") <+> quotes (ppr con_name) <+> ptext SLIT("has") <+> speakN n_flds]