X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=blobdiff_plain;f=compiler%2Ftypecheck%2FTcDeriv.lhs;h=4d1d448a24ad209fad447027bae61877f9d06488;hp=c4c885431ee1bc00b1cb2683c8b7c613de9a5957;hb=a3bab0506498db41853543558c52a4fda0d183af;hpb=4f567555306f33c96348eb3b363ca1cd51a9ef8b diff --git a/compiler/typecheck/TcDeriv.lhs b/compiler/typecheck/TcDeriv.lhs index c4c8854..4d1d448 100644 --- a/compiler/typecheck/TcDeriv.lhs +++ b/compiler/typecheck/TcDeriv.lhs @@ -68,10 +68,11 @@ Overall plan 3. Add the derived bindings, generating InstInfos + \begin{code} -- DerivSpec is purely local to this module data DerivSpec = DS { ds_loc :: SrcSpan - , ds_orig :: InstOrigin + , ds_orig :: CtOrigin , ds_name :: Name , ds_tvs :: [TyVar] , ds_theta :: ThetaType @@ -84,14 +85,27 @@ data DerivSpec = DS { ds_loc :: SrcSpan -- df :: forall tvs. theta => C tys -- The Name is the name for the DFun we'll build -- The tyvars bind all the variables in the theta - -- For family indexes, the tycon in + -- For type families, the tycon in -- in ds_tys is the *family* tycon -- in ds_tc, ds_tc_args is the *representation* tycon -- For non-family tycons, both are the same -- ds_newtype = True <=> Newtype deriving -- False <=> Vanilla deriving +\end{code} + +Example: + + newtype instance T [a] = MkT (Tree a) deriving( C s ) +==> + axiom T [a] = :RTList a + axiom :RTList a = Tree a + + DS { ds_tvs = [a,s], ds_cls = C, ds_tys = [s, T [a]] + , ds_tc = :RTList, ds_tc_args = [a] + , ds_newtype = True } +\begin{code} type DerivContext = Maybe ThetaType -- Nothing <=> Vanilla deriving; infer the context of the instance decl -- Just theta <=> Standalone deriving: context supplied by programmer @@ -287,7 +301,7 @@ tcDeriving tycl_decls inst_decls deriv_decls do { -- Fish the "deriving"-related information out of the TcEnv -- And make the necessary "equations". is_boot <- tcIsHsBoot - ; traceTc (text "tcDeriving" <+> ppr is_boot) + ; traceTc "tcDeriving" (ppr is_boot) ; early_specs <- makeDerivSpecs is_boot tycl_decls inst_decls deriv_decls ; overlap_flag <- getOverlapFlag @@ -338,10 +352,8 @@ renameDeriv is_boot gen_binds insts rm_dups [] $ concat deriv_aux_binds aux_val_binds = ValBindsIn (listToBag aux_binds) aux_sigs ; rn_aux_lhs <- rnTopBindsLHS emptyFsEnv aux_val_binds - ; let aux_names = collectHsValBinders rn_aux_lhs - - ; bindLocalNames aux_names $ - do { (rn_aux, dus_aux) <- rnTopBindsRHS (mkNameSet aux_names) rn_aux_lhs + ; bindLocalNames (collectHsValBinders rn_aux_lhs) $ + do { (rn_aux, dus_aux) <- rnTopBindsRHS rn_aux_lhs ; (rn_inst_infos, fvs_insts) <- mapAndUnzipM rn_inst_info inst_infos ; return (rn_inst_infos, rn_aux `plusHsValBinds` rn_gen, dus_gen `plusDU` dus_aux `plusDU` usesOnly (plusFVs fvs_insts)) } } @@ -361,14 +373,14 @@ renameDeriv is_boot gen_binds insts , mkFVs (map dataConName (tyConDataCons tc))) -- See Note [Newtype deriving and unused constructors] - rn_inst_info (InstInfo { iSpec = inst, iBinds = VanillaInst binds sigs standalone_deriv }) + rn_inst_info inst_info@(InstInfo { iSpec = inst, iBinds = VanillaInst binds sigs standalone_deriv }) = -- Bring the right type variables into -- scope (yuk), and rename the method binds ASSERT( null sigs ) bindLocalNames (map Var.varName tyvars) $ do { (rn_binds, fvs) <- rnMethodBinds clas_nm (\_ -> []) [] binds ; let binds' = VanillaInst rn_binds [] standalone_deriv - ; return (InstInfo { iSpec = inst, iBinds = binds' }, fvs) } + ; return (inst_info { iBinds = binds' }, fvs) } where (tyvars,_, clas,_) = instanceHead inst clas_nm = className clas @@ -454,21 +466,22 @@ deriveStandalone :: LDerivDecl Name -> TcM EarlyDerivSpec deriveStandalone (L loc (DerivDecl deriv_ty)) = setSrcSpan loc $ addErrCtxt (standaloneCtxt deriv_ty) $ - do { traceTc (text "standalone deriving decl for" <+> ppr deriv_ty) - ; (tvs, theta, tau) <- tcHsInstHead deriv_ty - ; traceTc (text "standalone deriving;" - <+> text "tvs:" <+> ppr tvs - <+> text "theta:" <+> ppr theta - <+> text "tau:" <+> ppr tau) - ; (cls, inst_tys) <- checkValidInstance deriv_ty tvs theta tau + do { traceTc "Standalone deriving decl for" (ppr deriv_ty) + ; (tvs, theta, cls, inst_tys) <- tcHsInstHead deriv_ty + ; traceTc "Standalone deriving;" $ vcat + [ text "tvs:" <+> ppr tvs + , text "theta:" <+> ppr theta + , text "cls:" <+> ppr cls + , text "tys:" <+> ppr inst_tys ] + ; checkValidInstance deriv_ty tvs theta cls inst_tys -- C.f. TcInstDcls.tcLocalInstDecl1 ; let cls_tys = take (length inst_tys - 1) inst_tys inst_ty = last inst_tys - ; traceTc (text "standalone deriving;" - <+> text "class:" <+> ppr cls - <+> text "class types:" <+> ppr cls_tys - <+> text "type:" <+> ppr inst_ty) + ; traceTc "Standalone deriving:" $ vcat + [ text "class:" <+> ppr cls + , text "class types:" <+> ppr cls_tys + , text "type:" <+> ppr inst_ty ] ; mkEqnHelp StandAloneDerivOrigin tvs cls cls_tys inst_ty (Just theta) } @@ -518,7 +531,7 @@ deriveTyData (L loc deriv_pred, L _ decl@(TyData { tcdLName = L _ tycon_name, -- Type families can't be partially applied -- e.g. newtype instance T Int a = MkT [a] deriving( Monad ) -- Note [Deriving, type families, and partial applications] - ; checkTc (not (isOpenTyCon tc) || n_args_to_drop == 0) + ; checkTc (not (isFamilyTyCon tc) || n_args_to_drop == 0) (typeFamilyPapErr tc cls cls_tys inst_ty) ; mkEqnHelp DerivOrigin (varSetElems univ_tvs) cls cls_tys inst_ty Nothing } } @@ -571,7 +584,7 @@ After all, we can write it out ... etc ... \begin{code} -mkEqnHelp :: InstOrigin -> [TyVar] -> Class -> [Type] -> Type +mkEqnHelp :: CtOrigin -> [TyVar] -> Class -> [Type] -> Type -> DerivContext -- Just => context supplied (standalone deriving) -- Nothing => context inferred (deriving on data decl) -> TcRn EarlyDerivSpec @@ -583,74 +596,46 @@ mkEqnHelp :: InstOrigin -> [TyVar] -> Class -> [Type] -> Type mkEqnHelp orig tvs cls cls_tys tc_app mtheta | Just (tycon, tc_args) <- tcSplitTyConApp_maybe tc_app , isAlgTyCon tycon -- Check for functions, primitive types etc - = do { (rep_tc, rep_tc_args) <- tcLookupFamInstExact tycon tc_args - -- Be careful to test rep_tc here: in the case of families, - -- we want to check the instance tycon, not the family tycon - - -- For standalone deriving (mtheta /= Nothing), - -- check that all the data constructors are in scope. - -- No need for this when deriving Typeable, becuase we don't need - -- the constructors for that. - ; rdr_env <- getGlobalRdrEnv - ; let hidden_data_cons = isAbstractTyCon rep_tc || any not_in_scope (tyConDataCons rep_tc) - not_in_scope dc = null (lookupGRE_Name rdr_env (dataConName dc)) - ; checkTc (isNothing mtheta || - not hidden_data_cons || - className cls `elem` typeableClassNames) - (derivingHiddenErr tycon) - - ; dflags <- getDOpts - ; if isDataTyCon rep_tc then - mkDataTypeEqn orig dflags tvs cls cls_tys - tycon tc_args rep_tc rep_tc_args mtheta - else - mkNewTypeEqn orig dflags tvs cls cls_tys - tycon tc_args rep_tc rep_tc_args mtheta } + = mk_alg_eqn tycon tc_args | otherwise = failWithTc (derivingThingErr False cls cls_tys tc_app (ptext (sLit "The last argument of the instance must be a data or newtype application"))) -\end{code} -Note [Looking up family instances for deriving] -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -tcLookupFamInstExact is an auxiliary lookup wrapper which requires -that looked-up family instances exist. If called with a vanilla -tycon, the old type application is simply returned. - -If we have - data instance F () = ... deriving Eq - data instance F () = ... deriving Eq -then tcLookupFamInstExact will be confused by the two matches; -but that can't happen because tcInstDecls1 doesn't call tcDeriving -if there are any overlaps. - -There are two other things that might go wrong with the lookup. -First, we might see a standalone deriving clause - deriving Eq (F ()) -when there is no data instance F () in scope. - -Note that it's OK to have - data instance F [a] = ... - deriving Eq (F [(a,b)]) -where the match is not exact; the same holds for ordinary data types -with standalone deriving declrations. + where + bale_out msg = failWithTc (derivingThingErr False cls cls_tys tc_app msg) -\begin{code} -tcLookupFamInstExact :: TyCon -> [Type] -> TcM (TyCon, [Type]) -tcLookupFamInstExact tycon tys - | not (isOpenTyCon tycon) - = return (tycon, tys) - | otherwise - = do { maybeFamInst <- tcLookupFamInst tycon tys - ; case maybeFamInst of - Nothing -> famInstNotFound tycon tys - Just famInst -> return famInst - } - -famInstNotFound :: TyCon -> [Type] -> TcM a -famInstNotFound tycon tys - = failWithTc (ptext (sLit "No family instance for") - <+> quotes (pprTypeApp tycon tys)) + mk_alg_eqn tycon tc_args + | className cls `elem` typeableClassNames + = do { dflags <- getDOpts + ; case checkTypeableConditions (dflags, tycon) of + Just err -> bale_out err + Nothing -> mk_typeable_eqn orig tvs cls tycon tc_args mtheta } + + | isDataFamilyTyCon tycon + , length tc_args /= tyConArity tycon + = bale_out (ptext (sLit "Unsaturated data family application")) + + | otherwise + = do { (rep_tc, rep_tc_args) <- tcLookupDataFamInst tycon tc_args + -- Be careful to test rep_tc here: in the case of families, + -- we want to check the instance tycon, not the family tycon + + -- For standalone deriving (mtheta /= Nothing), + -- check that all the data constructors are in scope. + ; rdr_env <- getGlobalRdrEnv + ; let hidden_data_cons = isAbstractTyCon rep_tc || + any not_in_scope (tyConDataCons rep_tc) + not_in_scope dc = null (lookupGRE_Name rdr_env (dataConName dc)) + ; unless (isNothing mtheta || not hidden_data_cons) + (bale_out (derivingHiddenErr tycon)) + + ; dflags <- getDOpts + ; if isDataTyCon rep_tc then + mkDataTypeEqn orig dflags tvs cls cls_tys + tycon tc_args rep_tc rep_tc_args mtheta + else + mkNewTypeEqn orig dflags tvs cls cls_tys + tycon tc_args rep_tc rep_tc_args mtheta } \end{code} @@ -661,7 +646,7 @@ famInstNotFound tycon tys %************************************************************************ \begin{code} -mkDataTypeEqn :: InstOrigin +mkDataTypeEqn :: CtOrigin -> DynFlags -> [Var] -- Universally quantified type variables in the instance -> Class -- Class for which we need to derive an instance @@ -685,15 +670,10 @@ mkDataTypeEqn orig dflags tvs cls cls_tys go_for_it = mk_data_eqn orig tvs cls tycon tc_args rep_tc rep_tc_args mtheta bale_out msg = failWithTc (derivingThingErr False cls cls_tys (mkTyConApp tycon tc_args) msg) -mk_data_eqn, mk_typeable_eqn - :: InstOrigin -> [TyVar] -> Class - -> TyCon -> [TcType] -> TyCon -> [TcType] -> DerivContext - -> TcM EarlyDerivSpec +mk_data_eqn :: CtOrigin -> [TyVar] -> Class + -> TyCon -> [TcType] -> TyCon -> [TcType] -> DerivContext + -> TcM EarlyDerivSpec mk_data_eqn orig tvs cls tycon tc_args rep_tc rep_tc_args mtheta - | getName cls `elem` typeableClassNames - = mk_typeable_eqn orig tvs cls tycon tc_args rep_tc rep_tc_args mtheta - - | otherwise = do { dfun_name <- new_dfun_name cls tycon ; loc <- getSrcSpanM ; let inst_tys = [mkTyConApp tycon tc_args] @@ -708,7 +688,11 @@ mk_data_eqn orig tvs cls tycon tc_args rep_tc rep_tc_args mtheta ; return (if isJust mtheta then Right spec -- Specified context else Left spec) } -- Infer context -mk_typeable_eqn orig tvs cls tycon tc_args rep_tc rep_tc_args mtheta +---------------------- +mk_typeable_eqn :: CtOrigin -> [TyVar] -> Class + -> TyCon -> [TcType] -> DerivContext + -> TcM EarlyDerivSpec +mk_typeable_eqn orig tvs cls tycon tc_args mtheta -- The Typeable class is special in several ways -- data T a b = ... deriving( Typeable ) -- gives @@ -722,7 +706,7 @@ mk_typeable_eqn orig tvs cls tycon tc_args rep_tc rep_tc_args mtheta = do { checkTc (cls `hasKey` typeableClassKey) (ptext (sLit "Use deriving( Typeable ) on a data type declaration")) ; real_cls <- tcLookupClass (typeableClassNames !! tyConArity tycon) - ; mk_typeable_eqn orig tvs real_cls tycon [] rep_tc [] (Just []) } + ; mk_typeable_eqn orig tvs real_cls tycon [] (Just []) } | otherwise -- standaone deriving = do { checkTc (null tc_args) @@ -733,17 +717,16 @@ mk_typeable_eqn orig tvs cls tycon tc_args rep_tc rep_tc_args mtheta ; return (Right $ DS { ds_loc = loc, ds_orig = orig, ds_name = dfun_name, ds_tvs = [] , ds_cls = cls, ds_tys = [mkTyConApp tycon []] - , ds_tc = rep_tc, ds_tc_args = rep_tc_args + , ds_tc = tycon, ds_tc_args = [] , ds_theta = mtheta `orElse` [], ds_newtype = False }) } - +---------------------- inferConstraints :: [TyVar] -> Class -> [TcType] -> TyCon -> [TcType] -> ThetaType -- Generate a sufficiently large set of constraints that typechecking the -- generated method definitions should succeed. This set will be simplified -- before being used in the instance declaration inferConstraints _ cls inst_tys rep_tc rep_tc_args = ASSERT2( equalLength rep_tc_tvs all_rep_tc_args, ppr cls <+> ppr rep_tc ) - pprTrace "ic" (ppr rep_tc $$ ppr rep_tc_tvs $$ ppr (tyConStupidTheta rep_tc) $$ ppr stupid_constraints) $ stupid_constraints ++ extra_constraints ++ sc_constraints ++ con_arg_constraints where @@ -823,6 +806,9 @@ checkSideConditions dflags mtheta cls cls_tys rep_tc where ty_args_why = quotes (ppr (mkClassPred cls cls_tys)) <+> ptext (sLit "is not a class") +checkTypeableConditions :: Condition +checkTypeableConditions = checkFlag Opt_DeriveDataTypeable `andCond` cond_typeableOK + nonStdErr :: Class -> SDoc nonStdErr cls = quotes (ppr cls) <+> ptext (sLit "is not a derivable class") @@ -843,7 +829,6 @@ sideConditions mtheta cls cond_functorOK False) -- Functor/Fold/Trav works ok for rank-n types | cls_key == traversableClassKey = Just (checkFlag Opt_DeriveTraversable `andCond` cond_functorOK False) - | getName cls `elem` typeableClassNames = Just (checkFlag Opt_DeriveDataTypeable `andCond` cond_typeableOK) | otherwise = Nothing where cls_key = getUnique cls @@ -859,11 +844,11 @@ type Condition = (DynFlags, TyCon) -> Maybe SDoc orCond :: Condition -> Condition -> Condition orCond c1 c2 tc = case c1 tc of - Nothing -> Nothing -- c1 succeeds - Just x -> case c2 tc of -- c1 fails + Nothing -> Nothing -- c1 succeeds + Just x -> case c2 tc of -- c1 fails Nothing -> Nothing Just y -> Just (x $$ ptext (sLit " and") $$ y) - -- Both fail + -- Both fail andCond :: Condition -> Condition -> Condition andCond c1 c2 tc = case c1 tc of @@ -874,16 +859,14 @@ cond_stdOK :: DerivContext -> Condition cond_stdOK (Just _) _ = Nothing -- Don't check these conservative conditions for -- standalone deriving; just generate the code + -- and let the typechecker handle the result cond_stdOK Nothing (_, rep_tc) - | null data_cons = Just (no_cons_why $$ suggestion) + | null data_cons = Just (no_cons_why rep_tc $$ suggestion) | not (null con_whys) = Just (vcat con_whys $$ suggestion) | otherwise = Nothing where suggestion = ptext (sLit "Possible fix: use a standalone deriving declaration instead") data_cons = tyConDataCons rep_tc - no_cons_why = quotes (pprSourceTyCon rep_tc) <+> - ptext (sLit "has no data constructors") - con_whys = mapCatMaybes check_con data_cons check_con :: DataCon -> Maybe SDoc @@ -892,6 +875,10 @@ cond_stdOK Nothing (_, rep_tc) , all isTauTy (dataConOrigArgTys con) = Nothing | otherwise = Just (badCon con (ptext (sLit "does not have a Haskell-98 type"))) +no_cons_why :: TyCon -> SDoc +no_cons_why rep_tc = quotes (pprSourceTyCon rep_tc) <+> + ptext (sLit "has no data constructors") + cond_enumOrProduct :: Condition cond_enumOrProduct = cond_isEnumeration `orCond` (cond_isProduct `andCond` cond_noUnliftedArgs) @@ -909,11 +896,13 @@ cond_noUnliftedArgs (_, tc) cond_isEnumeration :: Condition cond_isEnumeration (_, rep_tc) - | isEnumerationTyCon rep_tc = Nothing - | otherwise = Just why + | isEnumerationTyCon rep_tc = Nothing + | otherwise = Just why where - why = quotes (pprSourceTyCon rep_tc) <+> - ptext (sLit "has non-nullary constructors") + why = sep [ quotes (pprSourceTyCon rep_tc) <+> + ptext (sLit "is not an enumeration type") + , nest 2 $ ptext (sLit "(an enumeration consists of one or more nullary constructors)") ] + -- See Note [Enumeration types] in TyCon cond_isProduct :: Condition cond_isProduct (_, rep_tc) @@ -921,42 +910,50 @@ cond_isProduct (_, rep_tc) | otherwise = Just why where why = quotes (pprSourceTyCon rep_tc) <+> - ptext (sLit "has more than one constructor") + ptext (sLit "does not have precisely one constructor") cond_typeableOK :: Condition -- OK for Typeable class -- Currently: (a) args all of kind * -- (b) 7 or fewer args -cond_typeableOK (_, rep_tc) - | tyConArity rep_tc > 7 = Just too_many - | not (all (isSubArgTypeKind . tyVarKind) (tyConTyVars rep_tc)) - = Just bad_kind - | isFamInstTyCon rep_tc = Just fam_inst -- no Typable for family insts - | otherwise = Nothing +cond_typeableOK (_, tc) + | tyConArity tc > 7 = Just too_many + | not (all (isSubArgTypeKind . tyVarKind) (tyConTyVars tc)) + = Just bad_kind + | otherwise = Nothing where - too_many = quotes (pprSourceTyCon rep_tc) <+> + too_many = quotes (pprSourceTyCon tc) <+> ptext (sLit "has too many arguments") - bad_kind = quotes (pprSourceTyCon rep_tc) <+> + bad_kind = quotes (pprSourceTyCon tc) <+> ptext (sLit "has arguments of kind other than `*'") - fam_inst = quotes (pprSourceTyCon rep_tc) <+> - ptext (sLit "is a type family") - functorLikeClassKeys :: [Unique] functorLikeClassKeys = [functorClassKey, foldableClassKey, traversableClassKey] cond_functorOK :: Bool -> Condition --- OK for Functor class +-- OK for Functor/Foldable/Traversable class -- Currently: (a) at least one argument -- (b) don't use argument contravariantly -- (c) don't use argument in the wrong place, e.g. data T a = T (X a a) -- (d) optionally: don't use function types -cond_functorOK allowFunctions (dflags, rep_tc) - | not (dopt Opt_DeriveFunctor dflags) - = Just (ptext (sLit "You need -XDeriveFunctor to derive an instance for this class")) +-- (e) no "stupid context" on data type +cond_functorOK allowFunctions (_, rep_tc) + | null tc_tvs + = Just (ptext (sLit "Data type") <+> quotes (ppr rep_tc) + <+> ptext (sLit "has no parameters")) + + | not (null bad_stupid_theta) + = Just (ptext (sLit "Data type") <+> quotes (ppr rep_tc) + <+> ptext (sLit "has a class context") <+> pprTheta bad_stupid_theta) + | otherwise = msum (map check_con data_cons) -- msum picks the first 'Just', if any where + tc_tvs = tyConTyVars rep_tc + Just (_, last_tv) = snocView tc_tvs + bad_stupid_theta = filter is_bad (tyConStupidTheta rep_tc) + is_bad pred = last_tv `elemVarSet` tyVarsOfPred pred + data_cons = tyConDataCons rep_tc check_con con = msum (check_vanilla con : foldDataConArgs (ft_check con) con) @@ -981,7 +978,7 @@ cond_functorOK allowFunctions (dflags, rep_tc) checkFlag :: ExtensionFlag -> Condition checkFlag flag (dflags, _) - | dopt flag dflags = Nothing + | xopt flag dflags = Nothing | otherwise = Just why where why = ptext (sLit "You need -X") <> text flag_str @@ -1053,7 +1050,7 @@ a context for the Data instances: %************************************************************************ \begin{code} -mkNewTypeEqn :: InstOrigin -> DynFlags -> [Var] -> Class +mkNewTypeEqn :: CtOrigin -> DynFlags -> [Var] -> Class -> [Type] -> TyCon -> [Type] -> TyCon -> [Type] -> DerivContext -> TcRn EarlyDerivSpec @@ -1061,7 +1058,7 @@ mkNewTypeEqn orig dflags tvs cls cls_tys tycon tc_args rep_tycon rep_tc_args mtheta -- Want: instance (...) => cls (cls_tys ++ [tycon tc_args]) where ... | can_derive_via_isomorphism && (newtype_deriving || std_class_via_iso cls) - = do { traceTc (text "newtype deriving:" <+> ppr tycon <+> ppr rep_tys) + = do { traceTc "newtype deriving:" (ppr tycon <+> ppr rep_tys <+> ppr all_preds) ; dfun_name <- new_dfun_name cls tycon ; loc <- getSrcSpanM ; let spec = DS { ds_loc = loc, ds_orig = orig @@ -1084,7 +1081,7 @@ mkNewTypeEqn orig dflags tvs | can_derive_via_isomorphism -> bale_out (non_std $$ suggest_nd) -- Try newtype deriving! | otherwise -> bale_out non_std where - newtype_deriving = dopt Opt_GeneralizedNewtypeDeriving dflags + newtype_deriving = xopt Opt_GeneralizedNewtypeDeriving dflags go_for_it = mk_data_eqn orig tvs cls tycon tc_args rep_tycon rep_tc_args mtheta bale_out msg = failWithTc (derivingThingErr newtype_deriving cls cls_tys inst_ty msg) @@ -1242,7 +1239,7 @@ inferInstanceContexts :: OverlapFlag -> [DerivSpec] -> TcM [DerivSpec] inferInstanceContexts _ [] = return [] inferInstanceContexts oflag infer_specs - = do { traceTc (text "inferInstanceContexts" <+> vcat (map pprDerivSpec infer_specs)) + = do { traceTc "inferInstanceContexts" $ vcat (map pprDerivSpec infer_specs) ; iterate_deriv 1 initial_solutions } where ------------------------------------------------------------------ @@ -1285,21 +1282,26 @@ inferInstanceContexts oflag infer_specs , ds_cls = clas, ds_tys = inst_tys, ds_theta = deriv_rhs }) = setSrcSpan loc $ addErrCtxt (derivInstCtxt clas inst_tys) $ - do { theta <- tcSimplifyDeriv orig tyvars deriv_rhs - -- checkValidInstance tyvars theta clas inst_tys - -- Not necessary; see Note [Exotic derived instance contexts] - -- in TcSimplify - - -- Check for a bizarre corner case, when the derived instance decl should + do { -- Check for a bizarre corner case, when the derived instance decl should -- have form instance C a b => D (T a) where ... -- Note that 'b' isn't a parameter of T. This gives rise to all sorts -- of problems; in particular, it's hard to compare solutions for - -- equality when finding the fixpoint. So I just rule it out for now. + -- equality when finding the fixpoint. Moreover, simplifyDeriv + -- has an assert failure because it finds a TyVar when it expects + -- only TcTyVars. So I just rule it out for now. I'm not + -- even sure how it can arise. + ; let tv_set = mkVarSet tyvars - weird_preds = [pred | pred <- theta, not (tyVarsOfPred pred `subVarSet` tv_set)] + weird_preds = [pred | pred <- deriv_rhs + , not (tyVarsOfPred pred `subVarSet` tv_set)] ; mapM_ (addErrTc . badDerivedPred) weird_preds - ; traceTc (text "TcDeriv" <+> (ppr deriv_rhs $$ ppr theta)) + ; theta <- simplifyDeriv orig tyvars deriv_rhs + -- checkValidInstance tyvars theta clas inst_tys + -- Not necessary; see Note [Exotic derived instance contexts] + -- in TcSimplify + + ; traceTc "TcDeriv" (ppr deriv_rhs $$ ppr theta) -- Claim: the result instance declaration is guaranteed valid -- Hence no need to call: -- checkValidInstance tyvars theta clas inst_tys @@ -1399,33 +1401,35 @@ the renamer. What a great hack! genInst :: Bool -- True <=> standalone deriving -> OverlapFlag -> DerivSpec -> TcM (InstInfo RdrName, DerivAuxBinds) -genInst standalone_deriv oflag spec - | ds_newtype spec - = return (InstInfo { iSpec = mkInstance oflag (ds_theta spec) spec - , iBinds = NewTypeDerived co rep_tycon }, []) +genInst standalone_deriv oflag + spec@(DS { ds_tc = rep_tycon, ds_tc_args = rep_tc_args + , ds_theta = theta, ds_newtype = is_newtype + , ds_name = name, ds_cls = clas }) + | is_newtype + = return (InstInfo { iSpec = inst_spec + , iBinds = NewTypeDerived co rep_tycon }, []) | otherwise - = do { let loc = getSrcSpan (ds_name spec) - inst = mkInstance oflag (ds_theta spec) spec - clas = ds_cls spec - - -- In case of a family instance, we need to use the representation - -- tycon (after all, it has the data constructors) - ; fix_env <- getFixityEnv - ; let (meth_binds, aux_binds) = genDerivBinds loc fix_env clas rep_tycon - binds = VanillaInst meth_binds [] standalone_deriv - ; return (InstInfo { iSpec = inst, iBinds = binds }, aux_binds) - } + = do { fix_env <- getFixityEnv + ; let loc = getSrcSpan name + (meth_binds, aux_binds) = genDerivBinds loc fix_env clas rep_tycon + -- In case of a family instance, we need to use the representation + -- tycon (after all, it has the data constructors) + + ; return (InstInfo { iSpec = inst_spec + , iBinds = VanillaInst meth_binds [] standalone_deriv } + , aux_binds) } where - rep_tycon = ds_tc spec - rep_tc_args = ds_tc_args spec + inst_spec = mkInstance oflag theta spec co1 = case tyConFamilyCoercion_maybe rep_tycon of - Nothing -> IdCo Just co_con -> ACo (mkTyConApp co_con rep_tc_args) + Nothing -> id_co + -- Not a family => rep_tycon = main tycon co2 = case newTyConCo_maybe rep_tycon of - Nothing -> IdCo -- The newtype is transparent; no need for a cast Just co_con -> ACo (mkTyConApp co_con rep_tc_args) + Nothing -> id_co -- The newtype is transparent; no need for a cast co = co1 `mkTransCoI` co2 + id_co = IdCo (mkTyConApp rep_tycon rep_tc_args) -- Example: newtype instance N [a] = N1 (Tree a) -- deriving instance Eq b => Eq (N [(b,b)])