X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=blobdiff_plain;f=compiler%2Ftypecheck%2FTcDeriv.lhs;h=b994a278298bce08f124cf378c463459bc613af5;hp=ea38b34d04517c28bfc7c1907bdeb2fa2148cebc;hb=92267aa26adb1ab5a6d8004a80fdf6aa06ea4e44;hpb=24b1e13657c3e06e7c97eeab9a6c4f2a0cdd9193 diff --git a/compiler/typecheck/TcDeriv.lhs b/compiler/typecheck/TcDeriv.lhs index ea38b34..b994a27 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 @@ -48,6 +49,8 @@ import ListSetOps import Outputable import FastString import Bag + +import Control.Monad \end{code} %************************************************************************ @@ -65,25 +68,47 @@ 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 , 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 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 type EarlyDerivSpec = Either DerivSpec DerivSpec -- Left ds => the context for the instance should be inferred @@ -250,7 +275,12 @@ 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. %************************************************************************ %* * @@ -263,34 +293,35 @@ tcDeriving :: [LTyClDecl Name] -- All type constructors -> [LInstDecl Name] -- All instance declarations -> [LDerivDecl Name] -- All stand-alone deriving declarations -> TcM ([InstInfo Name], -- The generated "instance decls" - HsValBinds Name) -- Extra generated top-level bindings + HsValBinds Name, -- Extra generated top-level bindings + DefUses) tcDeriving tycl_decls inst_decls deriv_decls - = recoverM (return ([], emptyValBindsOut)) $ + = recoverM (return ([], emptyValBindsOut, emptyDUs)) $ 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 ; let (infer_specs, given_specs) = splitEithers early_specs - ; insts1 <- mapM (genInst overlap_flag) given_specs + ; insts1 <- mapM (genInst True overlap_flag) given_specs ; final_specs <- extendLocalInstEnv (map (iSpec . fst) insts1) $ inferInstanceContexts overlap_flag infer_specs - ; insts2 <- mapM (genInst overlap_flag) final_specs + ; insts2 <- mapM (genInst False overlap_flag) final_specs -- Generate the generic to/from functions from each type declaration - ; gen_binds <- mkGenericBinds is_boot - ; (inst_info, rn_binds) <- renameDeriv is_boot gen_binds (insts1 ++ insts2) + ; gen_binds <- mkGenericBinds is_boot tycl_decls + ; (inst_info, rn_binds, rn_dus) <- renameDeriv is_boot gen_binds (insts1 ++ insts2) ; dflags <- getDOpts ; 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 Name] -> HsValBinds Name -> SDoc ddump_deriving inst_infos extra_binds @@ -298,13 +329,13 @@ tcDeriving tycl_decls inst_decls deriv_decls renameDeriv :: Bool -> LHsBinds RdrName -> [(InstInfo RdrName, DerivAuxBinds)] - -> TcM ([InstInfo Name], HsValBinds Name) + -> 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 <- mapM rn_inst_info inst_infos - ; return (rn_inst_infos, emptyValBindsOut) } + = do { (rn_inst_infos, fvs) <- mapAndUnzipM rn_inst_info inst_infos + ; return (rn_inst_infos, emptyValBindsOut, usesOnly (plusFVs fvs)) } | otherwise = discardWarnings $ -- Discard warnings about unused bindings etc @@ -317,15 +348,15 @@ renameDeriv is_boot gen_binds insts -- 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) <- rnTopBindsRHS aux_names rn_aux_lhs - ; rn_inst_infos <- mapM rn_inst_info inst_infos - ; return (rn_inst_infos, rn_aux `plusHsValBinds` rn_gen) } } + ; let (aux_binds, aux_sigs) = unzip $ map (genAuxBind loc) $ + rm_dups [] $ concat deriv_aux_binds + aux_val_binds = ValBindsIn (listToBag aux_binds) aux_sigs + ; rn_aux_lhs <- rnTopBindsLHS emptyFsEnv aux_val_binds + ; 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)) } } where (inst_infos, deriv_aux_binds) = unzip insts @@ -336,35 +367,58 @@ renameDeriv is_boot gen_binds insts | otherwise = rm_dups (b:acc) bs - rn_inst_info (InstInfo { iSpec = inst, iBinds = NewTypeDerived }) - = return (InstInfo { iSpec = inst, iBinds = NewTypeDerived }) + rn_inst_info :: InstInfo RdrName -> TcM (InstInfo Name, FreeVars) + rn_inst_info info@(InstInfo { iBinds = NewTypeDerived coi tc }) + = return ( info { iBinds = NewTypeDerived coi tc } + , mkFVs (map dataConName (tyConDataCons tc))) + -- See Note [Newtype deriving and unused constructors] - rn_inst_info (InstInfo { iSpec = inst, iBinds = VanillaInst binds sigs }) + 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 - ; return (InstInfo { iSpec = inst, iBinds = VanillaInst rn_binds [] }) } + 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 + (tyvars,_, clas,_) = instanceHead inst + clas_nm = className clas ----------------------------------------- -mkGenericBinds :: Bool -> TcM (LHsBinds RdrName) -mkGenericBinds is_boot +mkGenericBinds :: Bool -> [LTyClDecl Name] -> TcM (LHsBinds RdrName) +mkGenericBinds is_boot tycl_decls | 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 ]) } + = do { tcs <- mapM tcLookupTyCon [ tcdName d + | L _ d <- tycl_decls, isDataDecl d ] + ; return (unionManyBags [ mkTyConGenericBinds tc + | tc <- tcs, tyConHasGenerics tc ]) } -- 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} +Note [Newtype deriving and unused constructors] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Consider this (see Trac #1954): + + module Bug(P) where + newtype P a = MkP (IO a) deriving Monad + +If you compile with -fwarn-unused-binds you do not expect the warning +"Defined but not used: data consructor MkP". Yet the newtype deriving +code does not explicitly mention MkP, but it should behave as if you +had written + instance Monad P where + return x = MkP (return x) + ...etc... + +So we want to signal a user of the data constructor 'MkP'. That's +what we do in rn_inst_info, and it's the only reason we have the TyCon +stored in NewTypeDerived. + %************************************************************************ %* * @@ -372,20 +426,7 @@ mkGenericBinds is_boot %* * %************************************************************************ -@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 :: Bool @@ -401,17 +442,14 @@ makeDerivSpecs is_boot tycl_decls inst_decls deriv_decls | 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] 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 ] + all_tydata = extractTyDataPreds (instDeclATs inst_decls ++ tycl_decls) deriv_locs = map (getLoc . snd) all_tydata ++ map getLoc deriv_decls @@ -421,63 +459,143 @@ makeDerivSpecs is_boot tycl_decls inst_decls deriv_decls 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 $ addErrCtxt (standaloneCtxt deriv_ty) $ - do { traceTc (text "standalone deriving decl for" <+> ppr deriv_ty) + do { traceTc "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) <- checkValidInstHead tau - ; checkValidInstance tvs theta cls inst_tys + ; traceTc "Standalone deriving;" $ vcat + [ text "tvs:" <+> ppr tvs + , text "theta:" <+> ppr theta + , text "tau:" <+> ppr tau ] + ; (cls, inst_tys) <- checkValidInstance deriv_ty tvs theta tau -- 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) } ------------------------------------------------------------------ -deriveTyData :: (LHsType Name, LTyClDecl Name) -> TcM (Maybe EarlyDerivSpec) +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 { 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 + 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 (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 } } + 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} ------------------------------------------------------------------- -mkEqnHelp :: InstOrigin -> [TyVar] -> Class -> [Type] -> Type - -> Maybe ThetaType -- Just => context supplied (standalone deriving) +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 (:CoS a)) : Eq [a] ~ Eq (S a) + instance Monad [] => Monad S -- by coercion sym (Monad :CoS) : 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 :: CtOrigin -> [TyVar] -> Class -> [Type] -> Type + -> DerivContext -- 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 , isAlgTyCon tycon -- Check for functions, primitive types etc - = do { (rep_tc, rep_tc_args) <- tcLookupFamInstExact tycon tc_args + = 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 @@ -485,8 +603,6 @@ mkEqnHelp orig tvs cls cls_tys tc_app mtheta -- 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. - -- By this time we know that the thing is algebraic - -- because we've called checkInstHead in derivingStandalone ; 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)) @@ -495,64 +611,16 @@ mkEqnHelp orig tvs cls cls_tys tc_app mtheta className cls `elem` typeableClassNames) (derivingHiddenErr tycon) - ; mayDeriveDataTypeable <- doptM Opt_DeriveDataTypeable - ; newtype_deriving <- doptM Opt_GeneralizedNewtypeDeriving - + ; 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 "The last argument of the instance must be a data or newtype application"))) - -baleOut :: Message -> TcM (Maybe a) -baleOut err = do { addErrTc err; return Nothing } -\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. - -\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)) + = 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} @@ -563,24 +631,34 @@ famInstNotFound 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 :: CtOrigin + -> 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 + -> DerivContext -- 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 + = case checkSideConditions dflags mtheta cls cls_tys rep_tc of -- 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 + 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 False 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) + :: 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 @@ -588,32 +666,19 @@ 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 @@ -635,11 +700,73 @@ mk_typeable_eqn orig tvs cls tycon tc_args rep_tc _rep_tc_args mtheta <> 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 _ 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 Data constraints + -- The Data class (only) requires that for + -- instance (...) => Data (T t1 t2) + -- IF t1:*, t2:* + -- THEN (Data t1, Data t2) are among the (...) constraints + -- Reason: when the IF holds, we generate a method + -- dataCast2 f = gcast2 f + -- and we need the Data constraints to typecheck the method + extra_constraints + | cls `hasKey` dataClassKey + , all (isLiftedTypeKind . typeKind) rep_tc_args + = [mkClassPred cls [ty] | ty <- rep_tc_args] + | otherwise + = [] + ------------------------------------------------------------------ -- Check side conditions that dis-allow derivability for particular classes -- This is *apart* from the newtype-deriving mechanism @@ -648,35 +775,52 @@ 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 -> DerivContext -> Class -> [TcType] -> TyCon -> DerivStatus +checkSideConditions dflags mtheta cls cls_tys rep_tc + | Just cond <- sideConditions mtheta cls + = case (cond (dflags, rep_tc)) of + Just err -> DerivableClassError err -- Class-specific error + Nothing | null cls_tys -> CanDerive -- All derivable classes are unary, so + -- cls_tys (the type args other than last) + -- should be null + | 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") - -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) + +nonStdErr :: Class -> SDoc +nonStdErr cls = quotes (ppr cls) <+> ptext (sLit "is not a derivable class") + +sideConditions :: DerivContext -> Class -> Maybe Condition +sideConditions mtheta cls + | 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 + cond_std = cond_stdOK mtheta -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 @@ -684,36 +828,65 @@ type Condition = (Bool, 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 Nothing -> c2 tc -- c1 succeeds Just x -> Just x -- c1 fails -cond_std :: Condition -cond_std (_, rep_tc) - | any (not . isVanillaDataCon) data_cons = Just existential_why - | null data_cons = Just no_cons_why - | otherwise = Nothing +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 rep_tc $$ suggestion) + | not (null con_whys) = Just (vcat con_whys $$ suggestion) + | 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)") + suggestion = ptext (sLit "Possible fix: use a standalone deriving declaration instead") + data_cons = tyConDataCons rep_tc + 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"))) +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) + +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 + | 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) @@ -721,7 +894,7 @@ 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 @@ -741,27 +914,99 @@ cond_typeableOK (_, rep_tc) fam_inst = quotes (pprSourceTyCon rep_tc) <+> ptext (sLit "is a type family") -cond_mayDeriveDataTypeable :: Condition -cond_mayDeriveDataTypeable (mayDeriveDataTypeable, _) - | mayDeriveDataTypeable = Nothing - | otherwise = Just why + +functorLikeClassKeys :: [Unique] +functorLikeClassKeys = [functorClassKey, foldableClassKey, traversableClassKey] + +cond_functorOK :: Bool -> Condition +-- 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 +-- (e) no "stupid context" on data type +cond_functorOK allowFunctions (dflags, rep_tc) + | not (xopt Opt_DeriveFunctor dflags) + = Just (ptext (sLit "You need -XDeriveFunctor to derive an instance for this class")) + + | 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) + + 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 :: ExtensionFlag -> Condition +checkFlag flag (dflags, _) + | xopt 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] +-- These standard classes can be derived for a newtype +-- using the isomorphism trick *even if no -XGeneralizedNewtypeDeriving +-- because giving so gives the same results as generating the boilerplate +std_class_via_iso clas + = classKey clas `elem` [eqClassKey, ordClassKey, ixClassKey, boundedClassKey] -- Not Read/Show because they respect the type -- Not Enum, because newtypes are never in Enum +non_iso_class :: Class -> Bool +-- *Never* derive Read,Show,Typeable,Data by isomorphism, +-- even with -XGeneralizedNewtypeDeriving +non_iso_class cls + = classKey cls `elem` ([readClassKey, showClassKey, dataClassKey] ++ + typeableClassKeys) + +typeableClassKeys :: [Unique] +typeableClassKeys = map getUnique typeableClassNames + new_dfun_name :: Class -> TyCon -> TcM Name new_dfun_name clas tycon -- Just a simple wrapper = 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] @@ -796,35 +1041,43 @@ a context for the Data instances: %************************************************************************ \begin{code} -mkNewTypeEqn :: InstOrigin -> Bool -> Bool -> [Var] -> Class +mkNewTypeEqn :: CtOrigin -> DynFlags -> [Var] -> Class -> [Type] -> TyCon -> [Type] -> TyCon -> [Type] - -> Maybe ThetaType - -> TcRn (Maybe EarlyDerivSpec) -mkNewTypeEqn orig mayDeriveDataTypeable newtype_deriving tvs + -> DerivContext + -> 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) + = 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 - , 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)) } - - | isNothing mb_std_err -- Use the standard H98 method - = mk_data_eqn orig tvs cls tycon tc_args rep_tycon rep_tc_args mtheta + ; return (if isJust mtheta then Right spec + else Left spec) } - -- 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 + | otherwise + = case checkSideConditions dflags mtheta cls cls_tys rep_tycon of + CanDerive -> go_for_it -- Use the standard H98 method + DerivableClassError msg -- Error with standard class + | can_derive_via_isomorphism -> bale_out (msg $$ suggest_nd) + | otherwise -> bale_out msg + NonDerivableClass -- Must use newtype deriving + | newtype_deriving -> bale_out cant_derive_err -- Too hard, even with newtype deriving + | can_derive_via_isomorphism -> bale_out (non_std $$ suggest_nd) -- Try newtype deriving! + | otherwise -> bale_out non_std 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 = 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) + + non_std = nonStdErr cls + suggest_nd = 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, ...) @@ -835,6 +1088,8 @@ 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)). @@ -854,15 +1109,12 @@ 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) + 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] -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ @@ -872,30 +1124,21 @@ mkNewTypeEqn orig mayDeriveDataTypeable newtype_deriving tvs -- 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) @@ -906,76 +1149,60 @@ 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_class cls = className cls `elem` ([readClassName, showClassName, dataClassName] ++ - typeableClassNames) can_derive_via_isomorphism = not (non_iso_class cls) - && 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 + && arity_ok + && eta_ok + && ats_ok +-- && not (isRecursiveTyCon tycon) -- Note [Recursive newtypes] + + 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 [ ppUnless arity_ok arity_msg + , ppUnless eta_ok eta_msg + , ppUnless ats_ok 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. + %************************************************************************ %* * @@ -1003,7 +1230,7 @@ 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 ------------------------------------------------------------------ @@ -1028,7 +1255,7 @@ inferInstanceContexts oflag infer_specs | 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 $ @@ -1046,31 +1273,34 @@ 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 + ; 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 ; 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 @@ -1159,29 +1389,46 @@ 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 RdrName, 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 rep_tycon }, []) | otherwise - = do { let loc = getSrcSpan (ds_name spec) - inst = mkInstance1 oflag spec - (_,_,clas,[ty]) = instanceHead inst - (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 ; fix_env <- getFixityEnv - ; let (meth_binds, aux_binds) = genDerivBinds loc fix_env clas tycon - - -- Build the InstInfo - ; return (InstInfo { iSpec = inst, - iBinds = VanillaInst meth_binds [] }, - aux_binds) + ; 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) } + where + rep_tycon = ds_tc spec + rep_tc_args = ds_tc_args spec + co1 = case tyConFamilyCoercion_maybe rep_tycon of + 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 + 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)]) +-- 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) +-- co : N [(b,b)] ~ Tree (b,b) genDerivBinds :: SrcSpan -> FixityEnv -> Class -> TyCon -> (LHsBinds RdrName, DerivAuxBinds) genDerivBinds loc fix_env clas tycon @@ -1202,6 +1449,9 @@ genDerivBinds loc fix_env clas tycon ,(showClassKey, gen_Show_binds fix_env) ,(readClassKey, gen_Read_binds fix_env) ,(dataClassKey, gen_Data_binds) + ,(functorClassKey, gen_Functor_binds) + ,(foldableClassKey, gen_Foldable_binds) + ,(traversableClassKey, gen_Traversable_binds) ] \end{code} @@ -1213,12 +1463,33 @@ genDerivBinds loc fix_env clas tycon %************************************************************************ \begin{code} -derivingThingErr :: Class -> [Type] -> Type -> Message -> Message -derivingThingErr clas tys ty why - = sep [hsep [ptext (sLit "Can't make a derived instance of"), - quotes (ppr pred)], - nest 2 (parens why)] +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 :: Bool -> Class -> [Type] -> Type -> Message -> Message +derivingThingErr newtype_deriving clas tys ty why + = sep [(hang (ptext (sLit "Can't make a derived instance of")) + 2 (quotes (ppr pred)) + $$ nest 2 extra) <> colon, + nest 2 why] where + extra | newtype_deriving = ptext (sLit "(even with cunning newtype deriving)") + | otherwise = empty pred = mkClassPred clas (tys ++ [ty]) derivingHiddenErr :: TyCon -> SDoc