X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Ftypecheck%2FTcDeriv.lhs;h=419ec948b24c617343de11af882a12de79ce4375;hb=960a5edb6ac87c7d85e36f4b70be8da0175819f7;hp=7a2954a6d5a4307c9e459904c93667623ec928e4;hpb=9319fbaf14f420cbbd9e670093cc86c5f04b7800;p=ghc-hetmet.git diff --git a/compiler/typecheck/TcDeriv.lhs b/compiler/typecheck/TcDeriv.lhs index 7a2954a..419ec94 100644 --- a/compiler/typecheck/TcDeriv.lhs +++ b/compiler/typecheck/TcDeriv.lhs @@ -74,13 +74,16 @@ data DerivSpec = DS { ds_loc :: SrcSpan , ds_theta :: ThetaType , ds_cls :: Class , ds_tys :: [Type] + , ds_tc :: TyCon , 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 is the *representation* tycon + -- For non-family tycons, both are the same -- ds_newtype = True <=> Newtype deriving -- False <=> Vanilla deriving @@ -269,7 +272,9 @@ tcDeriving tycl_decls inst_decls deriv_decls = recoverM (return ([], emptyValBindsOut)) $ 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 @@ -280,7 +285,6 @@ tcDeriving tycl_decls inst_decls deriv_decls ; insts2 <- mapM (genInst overlap_flag) final_specs - ; is_boot <- tcIsHsBoot -- 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) @@ -307,8 +311,8 @@ renameDeriv is_boot gen_binds insts | otherwise = discardWarnings $ -- Discard warnings about unused bindings etc - do { (rn_gen, dus_gen) <- setOptM Opt_PatternSignatures $ -- Type signatures in patterns - -- are used in the generic binds + 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 @@ -319,10 +323,10 @@ renameDeriv is_boot gen_binds insts ; 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) + ; let aux_names = map unLoc (collectHsValBinders rn_aux_lhs) ; bindLocalNames aux_names $ - do { (rn_aux, _dus) <- rnTopBindsRHS aux_names rn_aux_lhs + do { (rn_aux, _dus) <- rnTopBindsRHS (mkNameSet aux_names) rn_aux_lhs ; rn_inst_infos <- mapM rn_inst_info inst_infos ; return (rn_inst_infos, rn_aux `plusHsValBinds` rn_gen) } } @@ -371,44 +375,45 @@ 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 :: [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 $ @@ -433,32 +438,113 @@ deriveStandalone (L loc (DerivDecl deriv_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 (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 , isAlgTyCon tycon -- Check for functions, primitive types etc @@ -467,13 +553,15 @@ mkEqnHelp orig tvs cls cls_tys tc_app mtheta -- 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 + -- 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) + ; checkTc (isNothing mtheta || + not hidden_data_cons || + className cls `elem` typeableClassNames) (derivingHiddenErr tycon) ; mayDeriveDataTypeable <- doptM Opt_DeriveDataTypeable @@ -487,11 +575,8 @@ mkEqnHelp orig tvs cls cls_tys tc_app mtheta 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 } + = failWithTc (derivingThingErr cls cls_tys tc_app + (ptext (sLit "The last argument of the instance must be a data or newtype application"))) \end{code} Note [Looking up family instances for deriving] @@ -533,7 +618,7 @@ tcLookupFamInstExact tycon tys famInstNotFound :: TyCon -> [Type] -> TcM a famInstNotFound tycon tys = failWithTc (ptext (sLit "No family instance for") - <+> quotes (pprTypeApp tycon (ppr tycon) tys)) + <+> quotes (pprTypeApp tycon tys)) \end{code} @@ -546,22 +631,22 @@ famInstNotFound tycon tys \begin{code} mkDataTypeEqn :: InstOrigin -> Bool -> [Var] -> Class -> [Type] -> TyCon -> [Type] -> TyCon -> [Type] -> Maybe ThetaType - -> TcRn (Maybe EarlyDerivSpec) -- Return 'Nothing' if error + -> TcRn EarlyDerivSpec -- Return 'Nothing' if error mkDataTypeEqn orig mayDeriveDataTypeable tvs cls cls_tys tycon tc_args rep_tc rep_tc_args mtheta - | Just err <- checkSideConditions mayDeriveDataTypeable cls cls_tys rep_tc + = case checkSideConditions mayDeriveDataTypeable 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 -> mk_data_eqn orig tvs cls tycon tc_args rep_tc rep_tc_args mtheta + NonDerivableClass -> bale_out (nonStdErr cls) + DerivableClassError msg -> bale_out msg + where + 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 @@ -574,12 +659,14 @@ mk_data_eqn orig tvs cls tycon tc_args rep_tc rep_tc_args mtheta | 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? + not (isUnLiftedType arg_ty) ] + -- No constraints for unlifted types + -- Where they are legal we generate specilised function calls -- See Note [Superclasses of derived instance] sc_constraints = substTheta (zipOpenTvSubst (classTyVars cls) inst_tys) (classSCTheta cls) - inst_tys = [mkTyConApp tycon tc_args] + inst_tys = [mkTyConApp tycon tc_args] stupid_subst = zipTopTvSubst (tyConTyVars rep_tc) rep_tc_args stupid_constraints = substTheta stupid_subst (tyConStupidTheta rep_tc) @@ -587,12 +674,12 @@ mk_data_eqn orig tvs cls tycon tc_args rep_tc rep_tc_args mtheta spec = DS { ds_loc = loc, ds_orig = orig , ds_name = dfun_name, ds_tvs = tvs - , ds_cls = cls, ds_tys = inst_tys + , ds_cls = cls, ds_tys = inst_tys, ds_tc = rep_tc , ds_theta = mtheta `orElse` all_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 -- The Typeable class is special in several ways @@ -616,9 +703,9 @@ 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_theta = mtheta `orElse` [], ds_newtype = False }) } ------------------------------------------------------------------ @@ -629,28 +716,34 @@ 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 +data DerivStatus = CanDerive + | DerivableClassError SDoc -- Standard class, but can't do it + | NonDerivableClass -- Non-standard class + +checkSideConditions :: Bool -> Class -> [TcType] -> TyCon -> DerivStatus 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 + | Just cond <- sideConditions cls + = case (cond (mayDeriveDataTypeable, 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") + +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) + | 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 (cond_mayDeriveDataTypeable `andCond` cond_std `andCond` cond_noUnliftedArgs) | getName cls `elem` typeableClassNames = Just (cond_mayDeriveDataTypeable `andCond` cond_typeableOK) | otherwise = Nothing where @@ -688,6 +781,22 @@ cond_std (_, rep_tc) existential_why = quotes (pprSourceTyCon rep_tc) <+> ptext (sLit "has non-Haskell-98 constructor(s)") +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 = ptext (sLit "Constructor") <+> quotes (ppr (head bad_cons)) + <+> ptext (sLit "has arguments of unlifted type") + cond_isEnumeration :: Condition cond_isEnumeration (_, rep_tc) | isEnumerationTyCon rep_tc = Nothing @@ -780,32 +889,36 @@ a context for the Data instances: mkNewTypeEqn :: InstOrigin -> Bool -> Bool -> [Var] -> Class -> [Type] -> TyCon -> [Type] -> TyCon -> [Type] -> Maybe ThetaType - -> TcRn (Maybe EarlyDerivSpec) + -> TcRn EarlyDerivSpec mkNewTypeEqn orig mayDeriveDataTypeable newtype_deriving 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_cls = cls, ds_tys = inst_tys + , ds_name = dfun_name, ds_tvs = varSetElems dfun_tvs + , ds_cls = cls, ds_tys = inst_tys, ds_tc = rep_tycon , 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 check_conditions of + CanDerive -> mk_data_eqn orig tvs cls tycon tc_args rep_tycon rep_tc_args mtheta + -- 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")] + check_conditions = checkSideConditions mayDeriveDataTypeable cls cls_tys rep_tycon + 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, ...) @@ -816,6 +929,8 @@ 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)). @@ -835,15 +950,12 @@ 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 represenation 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] -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ @@ -853,30 +965,21 @@ 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) @@ -887,7 +990,6 @@ 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 ------------------------------------------------------------------- @@ -903,10 +1005,6 @@ mkNewTypeEqn orig mayDeriveDataTypeable newtype_deriving tvs && 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] @@ -922,39 +1020,25 @@ mkNewTypeEqn orig mayDeriveDataTypeable newtype_deriving tvs -- recursive newtypes too -- 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. + + cant_derive_err = 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 eta_ok then + ptext (sLit "cannot eta-reduce the representation type enough") + else empty + ] \end{code} @@ -1143,20 +1227,19 @@ the renamer. What a great hack! genInst :: OverlapFlag -> DerivSpec -> TcM (InstInfo RdrName, DerivAuxBinds) genInst oflag spec | ds_newtype spec - = return (InstInfo { iSpec = mkInstance1 oflag spec + = return (InstInfo { iSpec = mkInstance1 oflag spec , iBinds = NewTypeDerived }, []) | 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 = mkInstance1 oflag spec + clas = ds_cls spec + rep_tycon = ds_tc 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 + ; let (meth_binds, aux_binds) = genDerivBinds loc fix_env clas rep_tycon -- Build the InstInfo ; return (InstInfo { iSpec = inst, @@ -1194,6 +1277,24 @@ genDerivBinds loc fix_env clas 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"),