X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=blobdiff_plain;f=compiler%2Ftypecheck%2FTcDeriv.lhs;h=a24f1473148c75d7dd643fccf9320dac9f3a7799;hp=e79318b587700a97e8f585a487785337f47cf0bc;hb=aa0c0de94e25aa64139688f8e4c4ba51ddca6f54;hpb=162ae90572443ca726992ea54f4cbc75658453d3 diff --git a/compiler/typecheck/TcDeriv.lhs b/compiler/typecheck/TcDeriv.lhs index e79318b..a24f147 100644 --- a/compiler/typecheck/TcDeriv.lhs +++ b/compiler/typecheck/TcDeriv.lhs @@ -30,6 +30,7 @@ import HscTypes import Class import Type +import Coercion import ErrUtils import MkId import DataCon @@ -46,7 +47,10 @@ import SrcLoc import Util import ListSetOps import Outputable +import FastString import Bag + +import Control.Monad \end{code} %************************************************************************ @@ -73,13 +77,17 @@ data DerivSpec = DS { ds_loc :: SrcSpan , ds_theta :: ThetaType , ds_cls :: Class , ds_tys :: [Type] + , ds_tc :: TyCon + , ds_tc_args :: [Type] , ds_newtype :: Bool } -- This spec implies a dfun declaration of the form -- 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 is the *family* tycon - -- (not the representation tycon) + -- For family indexes, 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 @@ -249,7 +257,12 @@ There may be a coercion needed which we get from the tycon for the newtype when the dict is constructed in TcInstDcls.tcInstDecl2 - +Note [Unused constructors and deriving clauses] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +See Trac #3221. Consider + data T = T1 | T2 deriving( Show ) +Are T1 and T2 unused? Well, no: the deriving clause expands to mention +both of them. So we gather defs/uses from deriving just like anything else. %************************************************************************ %* * @@ -261,79 +274,110 @@ when the dict is constructed in TcInstDcls.tcInstDecl2 tcDeriving :: [LTyClDecl Name] -- All type constructors -> [LInstDecl Name] -- All instance declarations -> [LDerivDecl Name] -- All stand-alone deriving declarations - -> TcM ([InstInfo], -- The generated "instance decls" - HsValBinds Name) -- Extra generated top-level bindings + -> TcM ([InstInfo Name], -- The generated "instance decls" + HsValBinds Name, -- Extra generated top-level bindings + DefUses) tcDeriving tycl_decls inst_decls deriv_decls - = recoverM (returnM ([], emptyValBindsOut)) $ + = recoverM (return ([], emptyValBindsOut, emptyDUs)) $ do { -- Fish the "deriving"-related information out of the TcEnv -- And make the necessary "equations". - ; early_specs <- makeDerivSpecs tycl_decls inst_decls deriv_decls + is_boot <- tcIsHsBoot + ; traceTc (text "tcDeriving" <+> ppr is_boot) + ; early_specs <- makeDerivSpecs is_boot tycl_decls inst_decls deriv_decls ; overlap_flag <- getOverlapFlag ; let (infer_specs, given_specs) = splitEithers early_specs - ; (insts1, aux_binds1) <- mapAndUnzipM (genInst overlap_flag) given_specs + ; insts1 <- mapM (genInst True overlap_flag) given_specs - ; final_specs <- extendLocalInstEnv (map iSpec insts1) $ + ; final_specs <- extendLocalInstEnv (map (iSpec . fst) insts1) $ inferInstanceContexts overlap_flag infer_specs - ; (insts2, aux_binds2) <- mapAndUnzipM (genInst overlap_flag) final_specs - - ; is_boot <- tcIsHsBoot - ; rn_binds <- makeAuxBinds is_boot tycl_decls - (concat aux_binds1 ++ concat aux_binds2) + ; insts2 <- mapM (genInst False overlap_flag) final_specs - ; let inst_info = insts1 ++ insts2 + -- Generate the generic to/from functions from each type declaration + ; gen_binds <- mkGenericBinds is_boot + ; (inst_info, rn_binds, rn_dus) <- renameDeriv is_boot gen_binds (insts1 ++ insts2) ; dflags <- getDOpts - ; ioToTcRn (dumpIfSet_dyn dflags Opt_D_dump_deriv "Derived instances" - (ddump_deriving inst_info rn_binds)) + ; liftIO (dumpIfSet_dyn dflags Opt_D_dump_deriv "Derived instances" + (ddump_deriving inst_info rn_binds)) - ; return (inst_info, rn_binds) } + ; return (inst_info, rn_binds, rn_dus) } where - ddump_deriving :: [InstInfo] -> HsValBinds Name -> SDoc + ddump_deriving :: [InstInfo Name] -> HsValBinds Name -> SDoc ddump_deriving inst_infos extra_binds = vcat (map pprInstInfoDetails inst_infos) $$ ppr extra_binds -makeAuxBinds :: Bool -> [LTyClDecl Name] -> DerivAuxBinds -> TcM (HsValBinds Name) -makeAuxBinds is_boot tycl_decls deriv_aux_binds - | is_boot -- If we are compiling a hs-boot file, - -- don't generate any derived bindings - = return emptyValBindsOut +renameDeriv :: Bool -> LHsBinds RdrName + -> [(InstInfo RdrName, DerivAuxBinds)] + -> TcM ([InstInfo Name], HsValBinds Name, DefUses) +renameDeriv is_boot gen_binds insts + | is_boot -- If we are compiling a hs-boot file, don't generate any derived bindings + -- The inst-info bindings will all be empty, but it's easier to + -- just use rn_inst_info to change the type appropriately + = do { (rn_inst_infos, fvs) <- mapAndUnzipM rn_inst_info inst_infos + ; return (rn_inst_infos, emptyValBindsOut, usesOnly (plusFVs fvs)) } | otherwise - = do { let aux_binds = listToBag (map genAuxBind (rm_dups [] deriv_aux_binds)) - -- Generate any extra not-one-inst-decl-specific binds, + = discardWarnings $ -- Discard warnings about unused bindings etc + do { (rn_gen, dus_gen) <- setOptM Opt_ScopedTypeVariables $ -- Type signatures in patterns + -- are used in the generic binds + rnTopBinds (ValBindsIn gen_binds []) + ; keepAliveSetTc (duDefs dus_gen) -- Mark these guys to be kept alive + + -- Generate and rename any extra not-one-inst-decl-specific binds, -- notably "con2tag" and/or "tag2con" functions. + -- Bring those names into scope before renaming the instances themselves + ; loc <- getSrcSpanM -- Generic loc for shared bindings + ; let aux_binds = listToBag $ map (genAuxBind loc) $ + rm_dups [] $ concat deriv_aux_binds + ; rn_aux_lhs <- rnTopBindsLHS emptyFsEnv (ValBindsIn aux_binds []) + ; let aux_names = map unLoc (collectHsValBinders rn_aux_lhs) + + ; bindLocalNames aux_names $ + do { (rn_aux, dus_aux) <- rnTopBindsRHS (mkNameSet aux_names) 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)) } } - -- Generate the generic to/from functions from each type declaration - ; gen_binds <- mkGenericBinds tycl_decls - - -- Rename these extra bindings, discarding warnings about unused bindings etc - -- Type signatures in patterns are used in the generic binds - ; discardWarnings $ - setOptM Opt_PatternSignatures $ - do { (rn_deriv, _dus1) <- rnTopBinds (ValBindsIn aux_binds []) - ; (rn_gen, dus_gen) <- rnTopBinds (ValBindsIn gen_binds []) - ; keepAliveSetTc (duDefs dus_gen) -- Mark these guys to - -- be kept alive - ; return (rn_deriv `plusHsValBinds` rn_gen) } } where + (inst_infos, deriv_aux_binds) = unzip insts + -- Remove duplicate requests for auxilliary bindings rm_dups acc [] = acc rm_dups acc (b:bs) | any (isDupAux b) acc = rm_dups acc bs | otherwise = rm_dups (b:acc) bs + + rn_inst_info (InstInfo { iSpec = inst, iBinds = NewTypeDerived co }) + = return (InstInfo { iSpec = inst, iBinds = NewTypeDerived co }, emptyFVs) + + rn_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) } + where + (tyvars,_,clas,_) = instanceHead inst + clas_nm = className clas + ----------------------------------------- -mkGenericBinds :: [LTyClDecl Name] -> TcM (LHsBinds RdrName) -mkGenericBinds tycl_decls - = do { tcs <- mapM tcLookupTyCon - [ tc_name | - L _ (TyData { tcdLName = L _ tc_name }) <- tycl_decls] - -- We are only interested in the data type declarations +mkGenericBinds :: Bool -> TcM (LHsBinds RdrName) +mkGenericBinds is_boot + | is_boot + = return emptyBag + | otherwise + = do { gbl_env <- getGblEnv + ; let tcs = typeEnvTyCons (tcg_type_env gbl_env) ; return (unionManyBags [ mkTyConGenericBinds tc | tc <- tcs, tyConHasGenerics tc ]) } - -- And then only in the ones whose 'has-generics' flag is on + -- We are only interested in the data type declarations, + -- and then only in the ones whose 'has-generics' flag is on + -- The predicate tyConHasGenerics finds both of these \end{code} @@ -343,44 +387,45 @@ mkGenericBinds tycl_decls %* * %************************************************************************ -@makeDerivSpecs@ fishes around to find the info about needed derived -instances. Complicating factors: -\begin{itemize} -\item -We can only derive @Enum@ if the data type is an enumeration -type (all nullary data constructors). - -\item -We can only derive @Ix@ if the data type is an enumeration {\em -or} has just one data constructor (e.g., tuples). -\end{itemize} - -[See Appendix~E in the Haskell~1.2 report.] This code here deals w/ -all those. +@makeDerivSpecs@ fishes around to find the info about needed derived instances. \begin{code} -makeDerivSpecs :: [LTyClDecl Name] +makeDerivSpecs :: Bool + -> [LTyClDecl Name] -> [LInstDecl Name] -> [LDerivDecl Name] -> TcM [EarlyDerivSpec] -makeDerivSpecs tycl_decls inst_decls deriv_decls - = do { eqns1 <- mapAndRecoverM deriveTyData $ - extractTyDataPreds tycl_decls ++ - [ pd -- traverse assoc data families - | L _ (InstDecl _ _ _ ats) <- inst_decls - , pd <- extractTyDataPreds ats ] +makeDerivSpecs is_boot tycl_decls inst_decls deriv_decls + | is_boot -- No 'deriving' at all in hs-boot files + = do { mapM_ add_deriv_err deriv_locs + ; return [] } + | otherwise + = do { eqns1 <- mapAndRecoverM deriveTyData all_tydata ; eqns2 <- mapAndRecoverM deriveStandalone deriv_decls - ; return (catMaybes (eqns1 ++ eqns2)) } + ; return (eqns1 ++ eqns2) } where - extractTyDataPreds decls = - [(p, d) | d@(L _ (TyData {tcdDerivs = Just preds})) <- decls, p <- preds] + extractTyDataPreds decls + = [(p, d) | d@(L _ (TyData {tcdDerivs = Just preds})) <- decls, p <- preds] + + all_tydata :: [(LHsType Name, LTyClDecl Name)] + -- Derived predicate paired with its data type declaration + all_tydata = extractTyDataPreds tycl_decls ++ + [ pd -- Traverse assoc data families + | L _ (InstDecl _ _ _ ats) <- inst_decls + , pd <- extractTyDataPreds ats ] + + deriv_locs = map (getLoc . snd) all_tydata + ++ map getLoc deriv_decls + add_deriv_err loc = setSrcSpan loc $ + addErr (hang (ptext (sLit "Deriving not permitted in hs-boot file")) + 2 (ptext (sLit "Use an instance declaration instead"))) ------------------------------------------------------------------ -deriveStandalone :: LDerivDecl Name -> TcM (Maybe EarlyDerivSpec) +deriveStandalone :: LDerivDecl Name -> TcM EarlyDerivSpec -- Standalone deriving declarations --- e.g. deriving instance show a => Show (T a) +-- e.g. deriving instance Show a => Show (T a) -- Rather like tcLocalInstDecl deriveStandalone (L loc (DerivDecl deriv_ty)) = setSrcSpan loc $ @@ -392,9 +437,11 @@ deriveStandalone (L loc (DerivDecl deriv_ty)) <+> text "theta:" <+> ppr theta <+> text "tau:" <+> ppr tau) ; (cls, inst_tys) <- checkValidInstHead tau + ; checkValidInstance 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 @@ -403,70 +450,167 @@ deriveStandalone (L loc (DerivDecl deriv_ty)) (Just theta) } ------------------------------------------------------------------ -deriveTyData :: (LHsType Name, LTyClDecl Name) -> TcM (Maybe EarlyDerivSpec) -deriveTyData (deriv_pred, L loc decl@(TyData { tcdLName = L _ tycon_name, - tcdTyVars = tv_names, - tcdTyPats = ty_pats })) - = setSrcSpan loc $ - tcAddDeclCtxt decl $ - do { let hs_ty_args = ty_pats `orElse` map (nlHsTyVar . hsLTyVarName) tv_names - hs_app = nlHsTyConApp tycon_name hs_ty_args - -- We get kinding info for the tyvars by typechecking (T a b) - -- Hence forming a tycon application and then dis-assembling it - ; (tvs, tc_app) <- tcHsQuantifiedType tv_names hs_app +deriveTyData :: (LHsType Name, LTyClDecl Name) -> TcM EarlyDerivSpec +deriveTyData (L loc deriv_pred, L _ decl@(TyData { tcdLName = L _ tycon_name, + tcdTyVars = tv_names, + tcdTyPats = ty_pats })) + = setSrcSpan loc $ -- Use the location of the 'deriving' item + tcAddDeclCtxt decl $ + do { (tvs, tc, tc_args) <- get_lhs ty_pats ; tcExtendTyVarEnv tvs $ -- Deriving preds may (now) mention -- the type variables for the type constructor + do { (deriv_tvs, cls, cls_tys) <- tcHsDeriv deriv_pred -- The "deriv_pred" is a LHsType to take account of the fact that for -- newtype deriving we allow deriving (forall a. C [a]). - ; mkEqnHelp DerivOrigin (tvs++deriv_tvs) cls cls_tys tc_app Nothing } } + + -- Given data T a b c = ... deriving( C d ), + -- we want to drop type variables from T so that (C d (T a)) is well-kinded + ; let cls_tyvars = classTyVars cls + kind = tyVarKind (last cls_tyvars) + (arg_kinds, _) = splitKindFunTys kind + n_args_to_drop = length arg_kinds + n_args_to_keep = tyConArity tc - n_args_to_drop + args_to_drop = drop n_args_to_keep tc_args + inst_ty = mkTyConApp tc (take n_args_to_keep tc_args) + inst_ty_kind = typeKind inst_ty + dropped_tvs = mkVarSet (mapCatMaybes getTyVar_maybe args_to_drop) + univ_tvs = (mkVarSet tvs `extendVarSetList` deriv_tvs) + `minusVarSet` dropped_tvs + + -- Check that the result really is well-kinded + ; checkTc (n_args_to_keep >= 0 && (inst_ty_kind `eqKind` kind)) + (derivingKindErr tc cls cls_tys kind) + + ; checkTc (sizeVarSet dropped_tvs == n_args_to_drop && -- (a) + tyVarsOfTypes (inst_ty:cls_tys) `subVarSet` univ_tvs) -- (b) + (derivingEtaErr cls cls_tys inst_ty) + -- Check that + -- (a) The data type can be eta-reduced; eg reject: + -- data instance T a a = ... deriving( Monad ) + -- (b) The type class args do not mention any of the dropped type + -- variables + -- newtype T a s = ... deriving( ST s ) + + -- 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) + (typeFamilyPapErr tc cls cls_tys inst_ty) + + ; mkEqnHelp DerivOrigin (varSetElems univ_tvs) cls cls_tys inst_ty Nothing } } + where + -- Tiresomely we must figure out the "lhs", which is awkward for type families + -- E.g. data T a b = .. deriving( Eq ) + -- Here, the lhs is (T a b) + -- data instance TF Int b = ... deriving( Eq ) + -- Here, the lhs is (TF Int b) + -- But if we just look up the tycon_name, we get is the *family* + -- tycon, but not pattern types -- they are in the *rep* tycon. + get_lhs Nothing = do { tc <- tcLookupTyCon tycon_name + ; let tvs = tyConTyVars tc + ; return (tvs, tc, mkTyVarTys tvs) } + get_lhs (Just pats) = do { let hs_app = nlHsTyConApp tycon_name pats + ; (tvs, tc_app) <- tcHsQuantifiedType tv_names hs_app + ; let (tc, tc_args) = tcSplitTyConApp tc_app + ; return (tvs, tc, tc_args) } deriveTyData _other = panic "derivTyData" -- Caller ensures that only TyData can happen +\end{code} ------------------------------------------------------------------- +Note [Deriving, type families, and partial applications] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +When there are no type families, it's quite easy: + + newtype S a = MkS [a] + -- :CoS :: S ~ [] -- Eta-reduced + + instance Eq [a] => Eq (S a) -- by coercion sym (Eq (coMkS a)) : Eq [a] ~ Eq (S a) + instance Monad [] => Monad S -- by coercion sym (Monad coMkS) : Monad [] ~ Monad S + +When type familes are involved it's trickier: + + data family T a b + newtype instance T Int a = MkT [a] deriving( Eq, Monad ) + -- :RT is the representation type for (T Int a) + -- :CoF:R1T a :: T Int a ~ :RT a -- Not eta reduced + -- :Co:R1T :: :RT ~ [] -- Eta-reduced + + instance Eq [a] => Eq (T Int a) -- easy by coercion + instance Monad [] => Monad (T Int) -- only if we can eta reduce??? + +The "???" bit is that we don't build the :CoF thing in eta-reduced form +Henc the current typeFamilyPapErr, even though the instance makes sense. +After all, we can write it out + instance Monad [] => Monad (T Int) -- only if we can eta reduce??? + return x = MkT [x] + ... etc ... + +\begin{code} mkEqnHelp :: InstOrigin -> [TyVar] -> Class -> [Type] -> Type -> Maybe ThetaType -- Just => context supplied (standalone deriving) -- Nothing => context inferred (deriving on data decl) - -> TcRn (Maybe EarlyDerivSpec) + -> TcRn EarlyDerivSpec +-- Make the EarlyDerivSpec for an instance +-- forall tvs. theta => cls (tys ++ [ty]) +-- where the 'theta' is optional (that's the Maybe part) +-- Assumes that this declaration is well-kinded + mkEqnHelp orig tvs cls cls_tys tc_app mtheta | Just (tycon, tc_args) <- tcSplitTyConApp_maybe tc_app - = do { + , 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 - -- By this time we know that the thing is algebraic - -- because we've called checkInstHead in derivingStandalone - rdr_env <- getGlobalRdrEnv - ; let hidden_data_cons = filter not_in_scope (tyConDataCons tycon) - not_in_scope dc = null (lookupGRE_Name rdr_env (dataConName dc)) - ; checkTc (isNothing mtheta || null hidden_data_cons) + -- 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) - ; mayDeriveDataTypeable <- doptM Opt_DeriveDataTypeable - ; newtype_deriving <- doptM Opt_GeneralizedNewtypeDeriving - - ; (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 + ; dflags <- getDOpts ; if isDataTyCon rep_tc then - mkDataTypeEqn orig mayDeriveDataTypeable tvs cls cls_tys + mkDataTypeEqn orig dflags tvs cls cls_tys tycon tc_args rep_tc rep_tc_args mtheta else - mkNewTypeEqn orig mayDeriveDataTypeable newtype_deriving - tvs cls cls_tys + mkNewTypeEqn orig dflags tvs cls cls_tys tycon tc_args rep_tc rep_tc_args mtheta } | otherwise - = baleOut (derivingThingErr cls cls_tys tc_app - (ptext SLIT("Last argument of the instance must be a type application"))) - -baleOut :: Message -> TcM (Maybe a) -baleOut err = do { addErrTc err; return Nothing } + = failWithTc (derivingThingErr cls cls_tys tc_app + (ptext (sLit "The last argument of the instance must be a data or newtype application"))) \end{code} -Auxiliary lookup wrapper which requires that looked up family instances are -not type instances. If called with a vanilla tycon, the old type application -is simply returned. +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. \begin{code} tcLookupFamInstExact :: TyCon -> [Type] -> TcM (TyCon, [Type]) @@ -476,18 +620,14 @@ tcLookupFamInstExact tycon tys | otherwise = do { maybeFamInst <- tcLookupFamInst tycon tys ; case maybeFamInst of - Nothing -> famInstNotFound tycon tys False - Just famInst@(_, rep_tys) - | not variable_only_subst -> famInstNotFound tycon tys True - | otherwise -> return famInst - where - tvs = map (Type.getTyVar - "TcDeriv.tcLookupFamInstExact") - rep_tys - variable_only_subst = all Type.isTyVarTy rep_tys && - sizeVarSet (mkVarSet tvs) == length tvs - -- renaming may have no repetitions + 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)) \end{code} @@ -498,24 +638,34 @@ tcLookupFamInstExact tycon tys %************************************************************************ \begin{code} -mkDataTypeEqn :: InstOrigin -> Bool -> [Var] -> Class -> [Type] - -> TyCon -> [Type] -> TyCon -> [Type] -> Maybe ThetaType - -> TcRn (Maybe EarlyDerivSpec) -- Return 'Nothing' if error - -mkDataTypeEqn orig mayDeriveDataTypeable tvs cls cls_tys +mkDataTypeEqn :: InstOrigin + -> DynFlags + -> [Var] -- Universally quantified type variables in the instance + -> Class -- Class for which we need to derive an instance + -> [Type] -- Other parameters to the class except the last + -> TyCon -- Type constructor for which the instance is requested (last parameter to the type class) + -> [Type] -- Parameters to the type constructor + -> TyCon -- rep of the above (for type families) + -> [Type] -- rep of the above + -> Maybe ThetaType -- Context of the instance, for standalone deriving + -> TcRn EarlyDerivSpec -- Return 'Nothing' if error + +mkDataTypeEqn orig dflags tvs cls cls_tys tycon tc_args rep_tc rep_tc_args mtheta - | Just err <- checkSideConditions mayDeriveDataTypeable cls cls_tys rep_tc - -- NB: pass the *representation* tycon to checkSideConditions - = baleOut (derivingThingErr cls cls_tys (mkTyConApp tycon tc_args) err) - - | otherwise - = ASSERT( null cls_tys ) - mk_data_eqn orig tvs cls tycon tc_args rep_tc rep_tc_args mtheta + | isJust mtheta = go_for_it -- Do not test side conditions for standalone deriving + | otherwise = case checkSideConditions dflags cls cls_tys rep_tc of + -- NB: pass the *representation* tycon to checkSideConditions + CanDerive -> go_for_it + NonDerivableClass -> bale_out (nonStdErr cls) + DerivableClassError msg -> bale_out msg + where + go_for_it = mk_data_eqn orig tvs cls tycon tc_args rep_tc rep_tc_args mtheta + bale_out msg = failWithTc (derivingThingErr cls cls_tys (mkTyConApp tycon tc_args) msg) mk_data_eqn, mk_typeable_eqn :: InstOrigin -> [TyVar] -> Class -> TyCon -> [TcType] -> TyCon -> [TcType] -> Maybe ThetaType - -> TcM (Maybe EarlyDerivSpec) + -> 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 @@ -523,32 +673,19 @@ mk_data_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 ordinary_constraints - = [ mkClassPred cls [arg_ty] - | data_con <- tyConDataCons rep_tc, - arg_ty <- ASSERT( isVanillaDataCon data_con ) - dataConInstOrigArgTys data_con rep_tc_args, - not (isUnLiftedType arg_ty) ] -- No constraints for unlifted types? - - -- See Note [Superclasses of derived instance] - sc_constraints = substTheta (zipOpenTvSubst (classTyVars cls) inst_tys) - (classSCTheta cls) - inst_tys = [mkTyConApp tycon tc_args] - - stupid_subst = zipTopTvSubst (tyConTyVars rep_tc) rep_tc_args - stupid_constraints = substTheta stupid_subst (tyConStupidTheta rep_tc) - all_constraints = stupid_constraints ++ sc_constraints ++ ordinary_constraints - + ; let inst_tys = [mkTyConApp tycon tc_args] + inferred_constraints = inferConstraints tvs cls inst_tys rep_tc rep_tc_args spec = DS { ds_loc = loc, ds_orig = orig , ds_name = dfun_name, ds_tvs = tvs , ds_cls = cls, ds_tys = inst_tys - , ds_theta = mtheta `orElse` all_constraints + , ds_tc = rep_tc, ds_tc_args = rep_tc_args + , ds_theta = mtheta `orElse` inferred_constraints , ds_newtype = False } - ; return (if isJust mtheta then Just (Right spec) -- Specified context - else Just (Left spec)) } -- Infer context + ; 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 orig tvs cls tycon tc_args rep_tc rep_tc_args mtheta -- The Typeable class is special in several ways -- data T a b = ... deriving( Typeable ) -- gives @@ -560,21 +697,78 @@ mk_typeable_eqn orig tvs cls tycon tc_args rep_tc _rep_tc_args mtheta -- Typeable; it depends on the arity of the type | isNothing mtheta -- deriving on a data type decl = do { checkTc (cls `hasKey` typeableClassKey) - (ptext SLIT("Use deriving( Typeable ) on a data type declaration")) + (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 []) } | otherwise -- standaone deriving = do { checkTc (null tc_args) - (ptext SLIT("Derived typeable instance must be of form (Typeable") + (ptext (sLit "Derived typeable instance must be of form (Typeable") <> int (tyConArity tycon) <+> ppr tycon <> rparen) ; dfun_name <- new_dfun_name cls tycon ; loc <- getSrcSpanM - ; return (Just $ Right $ + ; return (Right $ DS { ds_loc = loc, ds_orig = orig, ds_name = dfun_name, ds_tvs = [] - , ds_cls = cls, ds_tys = [mkTyConApp tycon []] + , ds_cls = cls, ds_tys = [mkTyConApp tycon []] + , ds_tc = rep_tc, ds_tc_args = rep_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 tvs cls inst_tys rep_tc rep_tc_args + = ASSERT2( equalLength rep_tc_tvs all_rep_tc_args, ppr cls <+> ppr rep_tc ) + stupid_constraints ++ extra_constraints + ++ sc_constraints ++ con_arg_constraints + where + -- Constraints arising from the arguments of each constructor + con_arg_constraints + = [ mkClassPred cls [arg_ty] + | data_con <- tyConDataCons rep_tc, + arg_ty <- ASSERT( isVanillaDataCon data_con ) + get_constrained_tys $ + dataConInstOrigArgTys data_con all_rep_tc_args, + not (isUnLiftedType arg_ty) ] + -- No constraints for unlifted types + -- Where they are legal we generate specilised function calls + + -- For functor-like classes, two things are different + -- (a) We recurse over argument types to generate constraints + -- See Functor examples in TcGenDeriv + -- (b) The rep_tc_args will be one short + is_functor_like = getUnique cls `elem` functorLikeClassKeys + + get_constrained_tys :: [Type] -> [Type] + get_constrained_tys tys + | is_functor_like = concatMap (deepSubtypesContaining last_tv) tys + | otherwise = tys + + rep_tc_tvs = tyConTyVars rep_tc + last_tv = last rep_tc_tvs + all_rep_tc_args | is_functor_like = rep_tc_args ++ [mkTyVarTy last_tv] + | otherwise = rep_tc_args + + -- Constraints arising from superclasses + -- See Note [Superclasses of derived instance] + sc_constraints = substTheta (zipOpenTvSubst (classTyVars cls) inst_tys) + (classSCTheta cls) + + -- Stupid constraints + stupid_constraints = substTheta subst (tyConStupidTheta rep_tc) + subst = zipTopTvSubst rep_tc_tvs all_rep_tc_args + + -- Extra constraints + -- The Data class (only) requires that for + -- instance (...) => Data (T a b) + -- then (Data a, Data b) are among the (...) constraints + -- Reason: that's what you need to typecheck the method + -- dataCast1 f = gcast1 f + extra_constraints + | cls `hasKey` dataClassKey = [mkClassPred cls [mkTyVarTy tv] | tv <- tvs] + | otherwise = [] + ------------------------------------------------------------------ -- Check side conditions that dis-allow derivability for particular classes -- This is *apart* from the newtype-deriving mechanism @@ -583,35 +777,49 @@ mk_typeable_eqn orig tvs cls tycon tc_args rep_tc _rep_tc_args mtheta -- the data constructors - but we need to be careful to fall back to the -- family tycon (with indexes) in error messages. -checkSideConditions :: Bool -> Class -> [TcType] -> TyCon -> Maybe SDoc -checkSideConditions mayDeriveDataTypeable cls cls_tys rep_tc - | notNull cls_tys - = Just ty_args_why -- e.g. deriving( Foo s ) - | otherwise - = case sideConditions cls of - Just cond -> cond (mayDeriveDataTypeable, rep_tc) - Nothing -> Just non_std_why +data DerivStatus = CanDerive + | DerivableClassError SDoc -- Standard class, but can't do it + | NonDerivableClass -- Non-standard class + +checkSideConditions :: DynFlags -> Class -> [TcType] -> TyCon -> DerivStatus +checkSideConditions dflags cls cls_tys rep_tc + | Just cond <- sideConditions cls + = case (cond (dflags, rep_tc)) of + Just err -> DerivableClassError err -- Class-specific error + Nothing | null cls_tys -> CanDerive + | otherwise -> DerivableClassError ty_args_why -- e.g. deriving( Eq s ) + | otherwise = NonDerivableClass -- Not a standard class where - ty_args_why = quotes (ppr (mkClassPred cls cls_tys)) <+> ptext SLIT("is not a class") - non_std_why = quotes (ppr cls) <+> ptext SLIT("is not a derivable class") + ty_args_why = quotes (ppr (mkClassPred cls cls_tys)) <+> ptext (sLit "is not a class") + +nonStdErr :: Class -> SDoc +nonStdErr cls = quotes (ppr cls) <+> ptext (sLit "is not a derivable class") sideConditions :: Class -> Maybe Condition sideConditions cls - | cls_key == eqClassKey = Just cond_std - | cls_key == ordClassKey = Just cond_std - | cls_key == readClassKey = Just cond_std - | cls_key == showClassKey = Just cond_std - | cls_key == enumClassKey = Just (cond_std `andCond` cond_isEnumeration) - | cls_key == ixClassKey = Just (cond_std `andCond` (cond_isEnumeration `orCond` cond_isProduct)) - | cls_key == boundedClassKey = Just (cond_std `andCond` (cond_isEnumeration `orCond` cond_isProduct)) - | cls_key == dataClassKey = Just (cond_mayDeriveDataTypeable `andCond` cond_std) - | getName cls `elem` typeableClassNames = Just (cond_mayDeriveDataTypeable `andCond` cond_typeableOK) + | cls_key == eqClassKey = Just cond_std + | cls_key == ordClassKey = Just cond_std + | cls_key == showClassKey = Just cond_std + | cls_key == readClassKey = Just (cond_std `andCond` cond_noUnliftedArgs) + | cls_key == enumClassKey = Just (cond_std `andCond` cond_isEnumeration) + | cls_key == ixClassKey = Just (cond_std `andCond` cond_enumOrProduct) + | cls_key == boundedClassKey = Just (cond_std `andCond` cond_enumOrProduct) + | cls_key == dataClassKey = Just (checkFlag Opt_DeriveDataTypeable `andCond` + cond_std `andCond` cond_noUnliftedArgs) + | cls_key == functorClassKey = Just (checkFlag Opt_DeriveFunctor `andCond` + cond_functorOK True) -- NB: no cond_std! + | cls_key == foldableClassKey = Just (checkFlag Opt_DeriveFoldable `andCond` + 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 -type Condition = (Bool, TyCon) -> Maybe SDoc - -- Bool is whether or not we are allowed to derive Data and Typeable +type Condition = (DynFlags, TyCon) -> Maybe SDoc + -- first Bool is whether or not we are allowed to derive Data and Typeable + -- second Bool is whether or not we are allowed to derive Functor -- TyCon is the *representation* tycon if the -- data type is an indexed one -- Nothing => OK @@ -622,7 +830,7 @@ orCond c1 c2 tc Nothing -> Nothing -- c1 succeeds Just x -> case c2 tc of -- c1 fails Nothing -> Nothing - Just y -> Just (x $$ ptext SLIT(" and") $$ y) + Just y -> Just (x $$ ptext (sLit " and") $$ y) -- Both fail andCond :: Condition -> Condition -> Condition @@ -632,23 +840,44 @@ andCond c1 c2 tc = case c1 tc of cond_std :: Condition cond_std (_, rep_tc) - | any (not . isVanillaDataCon) data_cons = Just existential_why - | null data_cons = Just no_cons_why - | otherwise = Nothing + | null data_cons = Just no_cons_why + | not (null con_whys) = Just (vcat con_whys) + | otherwise = Nothing where data_cons = tyConDataCons rep_tc no_cons_why = quotes (pprSourceTyCon rep_tc) <+> - ptext SLIT("has no data constructors") - existential_why = quotes (pprSourceTyCon rep_tc) <+> - ptext SLIT("has non-Haskell-98 constructor(s)") + ptext (sLit "has no data constructors") + + con_whys = mapCatMaybes check_con data_cons + + check_con :: DataCon -> Maybe SDoc + check_con con + | isVanillaDataCon con + , all isTauTy (dataConOrigArgTys con) = Nothing + | otherwise = Just (badCon con (ptext (sLit "does not have a Haskell-98 type"))) +cond_enumOrProduct :: Condition +cond_enumOrProduct = cond_isEnumeration `orCond` + (cond_isProduct `andCond` cond_noUnliftedArgs) + +cond_noUnliftedArgs :: Condition +-- For some classes (eg Eq, Ord) we allow unlifted arg types +-- by generating specilaised code. For others (eg Data) we don't. +cond_noUnliftedArgs (_, tc) + | null bad_cons = Nothing + | otherwise = Just why + where + bad_cons = [ con | con <- tyConDataCons tc + , any isUnLiftedType (dataConOrigArgTys con) ] + why = badCon (head bad_cons) (ptext (sLit "has arguments of unlifted type")) + cond_isEnumeration :: Condition cond_isEnumeration (_, rep_tc) | isEnumerationTyCon rep_tc = Nothing | otherwise = Just why where why = quotes (pprSourceTyCon rep_tc) <+> - ptext SLIT("has non-nullary constructors") + ptext (sLit "has non-nullary constructors") cond_isProduct :: Condition cond_isProduct (_, rep_tc) @@ -656,7 +885,7 @@ cond_isProduct (_, rep_tc) | otherwise = Just why where why = quotes (pprSourceTyCon rep_tc) <+> - ptext SLIT("has more than one constructor") + ptext (sLit "has more than one constructor") cond_typeableOK :: Condition -- OK for Typeable class @@ -670,32 +899,78 @@ cond_typeableOK (_, rep_tc) | otherwise = Nothing where too_many = quotes (pprSourceTyCon rep_tc) <+> - ptext SLIT("has too many arguments") + ptext (sLit "has too many arguments") bad_kind = quotes (pprSourceTyCon rep_tc) <+> - ptext SLIT("has arguments of kind other than `*'") + ptext (sLit "has arguments of kind other than `*'") fam_inst = quotes (pprSourceTyCon rep_tc) <+> - ptext SLIT("is a type family") + ptext (sLit "is a type family") + + +functorLikeClassKeys :: [Unique] +functorLikeClassKeys = [functorClassKey, foldableClassKey, traversableClassKey] -cond_mayDeriveDataTypeable :: Condition -cond_mayDeriveDataTypeable (mayDeriveDataTypeable, _) - | mayDeriveDataTypeable = Nothing - | otherwise = Just why +cond_functorOK :: Bool -> Condition +-- OK for Functor 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")) + | otherwise + = msum (map check_con data_cons) -- msum picks the first 'Just', if any + where + data_cons = tyConDataCons rep_tc + check_con con = msum (check_vanilla con : foldDataConArgs (ft_check con) con) + + check_vanilla :: DataCon -> Maybe SDoc + check_vanilla con | isVanillaDataCon con = Nothing + | otherwise = Just (badCon con existential) + + ft_check :: DataCon -> FFoldType (Maybe SDoc) + ft_check con = FT { ft_triv = Nothing, ft_var = Nothing + , ft_co_var = Just (badCon con covariant) + , ft_fun = \x y -> if allowFunctions then x `mplus` y + else Just (badCon con functions) + , ft_tup = \_ xs -> msum xs + , ft_ty_app = \_ x -> x + , ft_bad_app = Just (badCon con wrong_arg) + , ft_forall = \_ x -> x } + + existential = ptext (sLit "has existential arguments") + covariant = ptext (sLit "uses the type variable in a function argument") + functions = ptext (sLit "contains function types") + wrong_arg = ptext (sLit "uses the type variable in an argument other than the last") + +checkFlag :: DynFlag -> Condition +checkFlag flag (dflags, _) + | dopt flag dflags = Nothing + | otherwise = Just why where - why = ptext SLIT("You need -XDeriveDataTypeable to derive an instance for this class") + why = ptext (sLit "You need -X") <> text flag_str + <+> ptext (sLit "to derive an instance for this class") + flag_str = case [ s | (s, f, _) <- xFlags, f==flag ] of + [s] -> s + other -> pprPanic "checkFlag" (ppr other) std_class_via_iso :: Class -> Bool std_class_via_iso clas -- These standard classes can be derived for a newtype -- using the isomorphism trick *even if no -fglasgow-exts* - = classKey clas `elem` [eqClassKey, ordClassKey, ixClassKey, boundedClassKey] + = classKey clas `elem` [eqClassKey, ordClassKey, ixClassKey, boundedClassKey] -- Not Read/Show because they respect the type -- Not Enum, because newtypes are never in Enum new_dfun_name :: Class -> TyCon -> TcM Name new_dfun_name clas tycon -- Just a simple wrapper - = newDFunName clas [mkTyConApp tycon []] (getSrcSpan tycon) + = do { loc <- getSrcSpanM -- The location of the instance decl, not of the tycon + ; newDFunName clas [mkTyConApp tycon []] loc } -- The type passed to newDFunName is only used to generate -- a suitable string; hence the empty type arg list + +badCon :: DataCon -> SDoc -> SDoc +badCon con msg = ptext (sLit "Constructor") <+> quotes (ppr con) <+> msg \end{code} Note [Superclasses of derived instance] @@ -730,35 +1005,41 @@ a context for the Data instances: %************************************************************************ \begin{code} -mkNewTypeEqn :: InstOrigin -> Bool -> Bool -> [Var] -> Class +mkNewTypeEqn :: InstOrigin -> DynFlags -> [Var] -> Class -> [Type] -> TyCon -> [Type] -> TyCon -> [Type] -> Maybe ThetaType - -> TcRn (Maybe EarlyDerivSpec) -mkNewTypeEqn orig mayDeriveDataTypeable newtype_deriving tvs + -> TcRn EarlyDerivSpec +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) ; dfun_name <- new_dfun_name cls tycon ; loc <- getSrcSpanM ; let spec = DS { ds_loc = loc, ds_orig = orig - , ds_name = dfun_name, ds_tvs = dict_tvs + , ds_name = dfun_name, ds_tvs = varSetElems dfun_tvs , ds_cls = cls, ds_tys = inst_tys + , ds_tc = rep_tycon, ds_tc_args = rep_tc_args , ds_theta = mtheta `orElse` all_preds , ds_newtype = True } - ; return (if isJust mtheta then Just (Right spec) - else Just (Left spec)) } + ; return (if isJust mtheta then Right spec + else Left spec) } - | isNothing mb_std_err -- Use the standard H98 method - = mk_data_eqn orig tvs cls tycon tc_args rep_tycon rep_tc_args mtheta - - -- Otherwise we can't derive - | newtype_deriving = baleOut cant_derive_err -- Too hard - | otherwise = baleOut std_err -- Just complain about being a non-std instance + | isJust mtheta = go_for_it -- Do not check side conditions for standalone deriving + | otherwise + = case checkSideConditions dflags cls cls_tys rep_tycon of + CanDerive -> go_for_it -- Use the standard H98 method + DerivableClassError msg -> bale_out msg -- Error with standard class + NonDerivableClass -- Must use newtype deriving + | newtype_deriving -> bale_out cant_derive_err -- Too hard, even with newtype deriving + | otherwise -> bale_out non_std_err -- Try newtype deriving! where - mb_std_err = checkSideConditions mayDeriveDataTypeable cls cls_tys rep_tycon - std_err = derivingThingErr cls cls_tys tc_app $ - vcat [fromJust mb_std_err, - ptext SLIT("Try -XGeneralizedNewtypeDeriving for GHC's newtype-deriving extension")] + newtype_deriving = dopt 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 cls cls_tys inst_ty msg) + + non_std_err = nonStdErr cls $$ + ptext (sLit "Try -XGeneralizedNewtypeDeriving for GHC's newtype-deriving extension") -- Here is the plan for newtype derivings. We see -- newtype T a1...an = MkT (t ak+1...an) deriving (.., C s1 .. sm, ...) @@ -769,6 +1050,8 @@ mkNewTypeEqn orig mayDeriveDataTypeable newtype_deriving tvs -- with the last parameter missing -- (T a1 .. ak) matches the kind of C's last argument -- (and hence so does t) + -- The latter kind-check has been done by deriveTyData already, + -- and tc_args are already trimmed -- -- We generate the instance -- instance forall ({a1..ak} u fvs(s1..sm)). @@ -788,48 +1071,36 @@ mkNewTypeEqn orig mayDeriveDataTypeable newtype_deriving tvs -- We generate the instance -- instance Monad (ST s) => Monad (T s) where - cls_tyvars = classTyVars cls - kind = tyVarKind (last cls_tyvars) - -- Kind of the thing we want to instance - -- e.g. argument kind of Monad, *->* - - (arg_kinds, _) = splitKindFunTys kind - n_args_to_drop = length arg_kinds - -- Want to drop 1 arg from (T s a) and (ST s a) - -- to get instance Monad (ST s) => Monad (T s) - - -- Note [newtype representation] - -- Need newTyConRhs *not* newTyConRep to get the representation - -- type, because the latter looks through all intermediate newtypes - -- For example + nt_eta_arity = length (fst (newTyConEtadRhs rep_tycon)) + -- For newtype T a b = MkT (S a a b), the TyCon machinery already + -- eta-reduces the representation type, so we know that + -- T a ~ S a a + -- That's convenient here, because we may have to apply + -- it to fewer than its original complement of arguments + + -- Note [Newtype representation] + -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + -- Need newTyConRhs (*not* a recursive representation finder) + -- to get the representation type. For example -- newtype B = MkB Int -- newtype A = MkA B deriving( Num ) -- We want the Num instance of B, *not* the Num instance of Int, -- when making the Num instance of A! - rep_ty = newTyConInstRhs rep_tycon rep_tc_args - (rep_fn, rep_ty_args) = tcSplitAppTys rep_ty - - n_tyargs_to_keep = tyConArity tycon - n_args_to_drop - dropped_tc_args = drop n_tyargs_to_keep tc_args - dropped_tvs = tyVarsOfTypes dropped_tc_args - - n_args_to_keep = length rep_ty_args - n_args_to_drop - args_to_drop = drop n_args_to_keep rep_ty_args - args_to_keep = take n_args_to_keep rep_ty_args - - rep_fn' = mkAppTys rep_fn args_to_keep - rep_tys = cls_tys ++ [rep_fn'] - rep_pred = mkClassPred cls rep_tys + rep_inst_ty = newTyConInstRhs rep_tycon rep_tc_args + rep_tys = cls_tys ++ [rep_inst_ty] + rep_pred = mkClassPred cls rep_tys -- rep_pred is the representation dictionary, from where -- we are gong to get all the methods for the newtype -- dictionary - tc_app = mkTyConApp tycon (take n_tyargs_to_keep tc_args) -- Next we figure out what superclass dictionaries to use -- See Note [Newtype deriving superclasses] above - inst_tys = cls_tys ++ [tc_app] + cls_tyvars = classTyVars cls + dfun_tvs = tyVarsOfTypes inst_tys + inst_ty = mkTyConApp tycon tc_args + inst_tys = cls_tys ++ [inst_ty] sc_theta = substTheta (zipOpenTvSubst cls_tyvars inst_tys) (classSCTheta cls) @@ -840,75 +1111,65 @@ mkNewTypeEqn orig mayDeriveDataTypeable newtype_deriving tvs -- instance C T -- rather than -- instance C Int => C T - dict_tvs = filterOut (`elemVarSet` dropped_tvs) tvs all_preds = rep_pred : sc_theta -- NB: rep_pred comes first ------------------------------------------------------------------- -- Figuring out whether we can only do this newtype-deriving thing - right_arity = length cls_tys + 1 == classArity cls - - -- Never derive Read,Show,Typeable,Data this way - non_iso_classes = [readClassKey, showClassKey, typeableClassKey, dataClassKey] can_derive_via_isomorphism - = not (getUnique cls `elem` non_iso_classes) - && right_arity -- Well kinded; - -- eg not: newtype T ... deriving( ST ) - -- because ST needs *2* type params - && n_tyargs_to_keep >= 0 -- Type constructor has right kind: - -- eg not: newtype T = T Int deriving( Monad ) - && n_args_to_keep >= 0 -- Rep type has right kind: - -- eg not: newtype T a = T Int deriving( Monad ) - && eta_ok -- Eta reduction works - && not (isRecursiveTyCon tycon) -- Does not work for recursive tycons: - -- newtype A = MkA [A] - -- Don't want - -- instance Eq [A] => Eq A !! - -- Here's a recursive newtype that's actually OK - -- newtype S1 = S1 [T1 ()] - -- newtype T1 a = T1 (StateT S1 IO a ) deriving( Monad ) - -- It's currently rejected. Oh well. - -- In fact we generate an instance decl that has method of form - -- meth @ instTy = meth @ repTy - -- (no coerce's). We'd need a coerce if we wanted to handle - -- recursive newtypes too + = not (non_iso_class cls) + && arity_ok + && eta_ok + && ats_ok +-- && not (isRecursiveTyCon tycon) -- Note [Recursive newtypes] + + -- Never derive Read,Show,Typeable,Data by isomorphism + non_iso_class cls = className cls `elem` ([readClassName, showClassName, dataClassName] ++ + typeableClassNames) + + arity_ok = length cls_tys + 1 == classArity cls + -- Well kinded; eg not: newtype T ... deriving( ST ) + -- because ST needs *2* type params -- Check that eta reduction is OK - eta_ok = (args_to_drop `tcEqTypes` dropped_tc_args) - -- (a) the dropped-off args are identical in the source and rep type + eta_ok = nt_eta_arity <= length rep_tc_args + -- The newtype can be eta-reduced to match the number + -- of type argument actually supplied -- newtype T a b = MkT (S [a] b) deriving( Monad ) -- Here the 'b' must be the same in the rep type (S [a] b) - - && (tyVarsOfType rep_fn' `disjointVarSet` dropped_tvs) - -- (b) the remaining type args do not mention any of the dropped - -- type variables - - && (tyVarsOfTypes cls_tys `disjointVarSet` dropped_tvs) - -- (c) the type class args do not mention any of the dropped type - -- variables - - && all isTyVarTy dropped_tc_args - -- (d) in case of newtype family instances, the eta-dropped - -- arguments must be type variables (not more complex indexes) - - cant_derive_err = derivingThingErr cls cls_tys tc_app - (vcat [ptext SLIT("even with cunning newtype deriving:"), - if isRecursiveTyCon tycon then - ptext SLIT("the newtype may be recursive") - else empty, - if not right_arity then - quotes (ppr (mkClassPred cls cls_tys)) <+> ptext SLIT("does not have arity 1") - else empty, - if not (n_tyargs_to_keep >= 0) then - ptext SLIT("the type constructor has wrong kind") - else if not (n_args_to_keep >= 0) then - ptext SLIT("the representation type has wrong kind") - else if not eta_ok then - ptext SLIT("the eta-reduction property does not hold") - else empty - ]) + -- And the [a] must not mention 'b'. That's all handled + -- by nt_eta_rity. + + ats_ok = null (classATs cls) + -- No associated types for the class, because we don't + -- currently generate type 'instance' decls; and cannot do + -- so for 'data' instance decls + + cant_derive_err + = vcat [ ptext (sLit "even with cunning newtype deriving:") + , if arity_ok then empty else arity_msg + , if eta_ok then empty else eta_msg + , if ats_ok then empty else ats_msg ] + arity_msg = quotes (ppr (mkClassPred cls cls_tys)) <+> ptext (sLit "does not have arity 1") + eta_msg = ptext (sLit "cannot eta-reduce the representation type enough") + ats_msg = ptext (sLit "the class has associated types") \end{code} +Note [Recursive newtypes] +~~~~~~~~~~~~~~~~~~~~~~~~~ +Newtype deriving works fine, even if the newtype is recursive. +e.g. newtype S1 = S1 [T1 ()] + newtype T1 a = T1 (StateT S1 IO a ) deriving( Monad ) +Remember, too, that type families are curretly (conservatively) given +a recursive flag, so this also allows newtype deriving to work +for type famillies. + +We used to exclude recursive types, because we had a rather simple +minded way of generating the instance decl: + newtype A = MkA [A] + instance Eq [A] => Eq A -- Makes typechecker loop! +But now we require a simple context, so it's ok. + %************************************************************************ %* * @@ -954,14 +1215,14 @@ inferInstanceContexts oflag infer_specs iterate_deriv :: Int -> [ThetaType] -> TcM [DerivSpec] iterate_deriv n current_solns | n > 20 -- Looks as if we are in an infinite loop - -- This can happen if we have -fallow-undecidable-instances + -- This can happen if we have -XUndecidableInstances -- (See TcSimplify.tcSimplifyDeriv.) = pprPanic "solveDerivEqns: probable loop" (vcat (map pprDerivSpec infer_specs) $$ ppr current_solns) | otherwise = do { -- Extend the inst info from the explicit instance decls -- with the current set of solutions, and simplify each RHS - let inst_specs = zipWithEqual "add_solns" (mkInstance2 oflag) + let inst_specs = zipWithEqual "add_solns" (mkInstance oflag) current_solns infer_specs ; new_solns <- checkNoErrs $ extendLocalInstEnv inst_specs $ @@ -999,11 +1260,8 @@ inferInstanceContexts oflag infer_specs ; return (sortLe (<=) theta) } -- Canonicalise before returning the solution ------------------------------------------------------------------ -mkInstance1 :: OverlapFlag -> DerivSpec -> Instance -mkInstance1 overlap_flag spec = mkInstance2 overlap_flag (ds_theta spec) spec - -mkInstance2 :: OverlapFlag -> ThetaType -> DerivSpec -> Instance -mkInstance2 overlap_flag theta +mkInstance :: OverlapFlag -> ThetaType -> DerivSpec -> Instance +mkInstance overlap_flag theta (DS { ds_name = dfun_name , ds_tvs = tyvars, ds_cls = clas, ds_tys = tys }) = mkLocalInstance dfun overlap_flag @@ -1092,50 +1350,55 @@ the renamer. What a great hack! -- Representation tycons differ from the tycon in the instance signature in -- case of instances for indexed families. -- -genInst :: OverlapFlag -> DerivSpec -> TcM (InstInfo, DerivAuxBinds) -genInst oflag spec +genInst :: Bool -- True <=> standalone deriving + -> OverlapFlag + -> DerivSpec -> TcM (InstInfo RdrName, DerivAuxBinds) +genInst standalone_deriv oflag spec | ds_newtype spec - = return (InstInfo { iSpec = mkInstance1 oflag spec - , iBinds = NewTypeDerived }, []) + = return (InstInfo { iSpec = mkInstance oflag (ds_theta spec) spec + , iBinds = NewTypeDerived co }, []) | otherwise - = do { fix_env <- getFixityEnv - ; let - inst = mkInstance1 oflag spec - (tyvars,_,clas,[ty]) = instanceHead inst - clas_nm = className clas - (visible_tycon, tyArgs) = tcSplitTyConApp ty + = 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) - ; (tycon, _) <- tcLookupFamInstExact visible_tycon tyArgs - ; let (meth_binds, aux_binds) = genDerivBinds clas fix_env tycon - - -- Bring the right type variables into - -- scope, and rename the method binds - -- It's a bit yukky that we return *renamed* InstInfo, but - -- *non-renamed* auxiliary bindings - ; (rn_meth_binds, _fvs) <- discardWarnings $ - bindLocalNames (map Var.varName tyvars) $ - rnMethodBinds clas_nm (\_ -> []) [] meth_binds - - -- Build the InstInfo - ; return (InstInfo { iSpec = inst, - iBinds = VanillaInst rn_meth_binds [] }, - aux_binds) + ; 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) } - -genDerivBinds :: Class -> FixityEnv -> TyCon -> (LHsBinds RdrName, DerivAuxBinds) -genDerivBinds clas fix_env tycon + where + rep_tycon = ds_tc spec + rep_tc_args = ds_tc_args spec + co1 = case tyConFamilyCoercion_maybe rep_tycon of + Nothing -> IdCo + Just co_con -> ACo (mkTyConApp co_con rep_tc_args) + 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) + co = co1 `mkTransCoI` co2 + +-- Example: newtype instance N [a] = N1 (Tree a) +-- deriving instance Eq b => Eq (N [(b,b)]) +-- From the instance, we get an implicit newtype R1:N a = N1 (Tree a) +-- When dealing with the deriving clause +-- co1 : N [(b,b)] ~ R1:N (b,b) +-- co2 : R1:N (b,b) ~ Tree (b,b) + +genDerivBinds :: SrcSpan -> FixityEnv -> Class -> TyCon -> (LHsBinds RdrName, DerivAuxBinds) +genDerivBinds loc fix_env clas tycon | className clas `elem` typeableClassNames - = (gen_Typeable_binds tycon, []) + = (gen_Typeable_binds loc tycon, []) | otherwise = case assocMaybe gen_list (getUnique clas) of - Just gen_fn -> gen_fn tycon + Just gen_fn -> gen_fn loc tycon Nothing -> pprPanic "genDerivBinds: bad derived class" (ppr clas) where - gen_list :: [(Unique, TyCon -> (LHsBinds RdrName, DerivAuxBinds))] + gen_list :: [(Unique, SrcSpan -> TyCon -> (LHsBinds RdrName, DerivAuxBinds))] gen_list = [(eqClassKey, gen_Eq_binds) ,(ordClassKey, gen_Ord_binds) ,(enumClassKey, gen_Enum_binds) @@ -1143,7 +1406,10 @@ genDerivBinds clas fix_env tycon ,(ixClassKey, gen_Ix_binds) ,(showClassKey, gen_Show_binds fix_env) ,(readClassKey, gen_Read_binds fix_env) - ,(dataClassKey, gen_Data_binds fix_env) + ,(dataClassKey, gen_Data_binds) + ,(functorClassKey, gen_Functor_binds) + ,(foldableClassKey, gen_Foldable_binds) + ,(traversableClassKey, gen_Traversable_binds) ] \end{code} @@ -1155,9 +1421,27 @@ genDerivBinds clas fix_env tycon %************************************************************************ \begin{code} +derivingKindErr :: TyCon -> Class -> [Type] -> Kind -> Message +derivingKindErr tc cls cls_tys cls_kind + = hang (ptext (sLit "Cannot derive well-kinded instance of form") + <+> quotes (pprClassPred cls cls_tys <+> parens (ppr tc <+> ptext (sLit "...")))) + 2 (ptext (sLit "Class") <+> quotes (ppr cls) + <+> ptext (sLit "expects an argument of kind") <+> quotes (pprKind cls_kind)) + +derivingEtaErr :: Class -> [Type] -> Type -> Message +derivingEtaErr cls cls_tys inst_ty + = sep [ptext (sLit "Cannot eta-reduce to an instance of form"), + nest 2 (ptext (sLit "instance (...) =>") + <+> pprClassPred cls (cls_tys ++ [inst_ty]))] + +typeFamilyPapErr :: TyCon -> Class -> [Type] -> Type -> Message +typeFamilyPapErr tc cls cls_tys inst_ty + = hang (ptext (sLit "Derived instance") <+> quotes (pprClassPred cls (cls_tys ++ [inst_ty]))) + 2 (ptext (sLit "requires illegal partial application of data type family") <+> ppr tc) + derivingThingErr :: Class -> [Type] -> Type -> Message -> Message derivingThingErr clas tys ty why - = sep [hsep [ptext SLIT("Can't make a derived instance of"), + = sep [hsep [ptext (sLit "Can't make a derived instance of"), quotes (ppr pred)], nest 2 (parens why)] where @@ -1165,28 +1449,20 @@ derivingThingErr clas tys ty why derivingHiddenErr :: TyCon -> SDoc derivingHiddenErr tc - = hang (ptext SLIT("The data constructors of") <+> quotes (ppr tc) <+> ptext SLIT("are not all in scope")) - 2 (ptext SLIT("so you cannot derive an instance for it")) + = hang (ptext (sLit "The data constructors of") <+> quotes (ppr tc) <+> ptext (sLit "are not all in scope")) + 2 (ptext (sLit "so you cannot derive an instance for it")) standaloneCtxt :: LHsType Name -> SDoc -standaloneCtxt ty = hang (ptext SLIT("In the stand-alone deriving instance for")) +standaloneCtxt ty = hang (ptext (sLit "In the stand-alone deriving instance for")) 2 (quotes (ppr ty)) derivInstCtxt :: Class -> [Type] -> Message derivInstCtxt clas inst_tys - = ptext SLIT("When deriving the instance for") <+> parens (pprClassPred clas inst_tys) + = ptext (sLit "When deriving the instance for") <+> parens (pprClassPred clas inst_tys) badDerivedPred :: PredType -> Message badDerivedPred pred - = vcat [ptext SLIT("Can't derive instances where the instance context mentions"), - ptext SLIT("type variables that are not data type parameters"), - nest 2 (ptext SLIT("Offending constraint:") <+> ppr pred)] - -famInstNotFound :: TyCon -> [Type] -> Bool -> TcM a -famInstNotFound tycon tys notExact - = failWithTc (msg <+> quotes (pprTypeApp tycon (ppr tycon) tys)) - where - msg = ptext $ if notExact - then SLIT("No family instance exactly matching") - else SLIT("More than one family instance for") + = vcat [ptext (sLit "Can't derive instances where the instance context mentions"), + ptext (sLit "type variables that are not data type parameters"), + nest 2 (ptext (sLit "Offending constraint:") <+> ppr pred)] \end{code}