X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=blobdiff_plain;f=compiler%2Ftypecheck%2FTcDeriv.lhs;h=a24f1473148c75d7dd643fccf9320dac9f3a7799;hp=419ec948b24c617343de11af882a12de79ce4375;hb=aa0c0de94e25aa64139688f8e4c4ba51ddca6f54;hpb=a854a0b9cefefe8cc8e96125ff13489bf96bf5a6 diff --git a/compiler/typecheck/TcDeriv.lhs b/compiler/typecheck/TcDeriv.lhs index 419ec94..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 @@ -48,6 +49,8 @@ import ListSetOps import Outputable import FastString import Bag + +import Control.Monad \end{code} %************************************************************************ @@ -75,6 +78,7 @@ data DerivSpec = DS { ds_loc :: SrcSpan , 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 @@ -82,7 +86,7 @@ data DerivSpec = DS { ds_loc :: SrcSpan -- The tyvars bind all the variables in the theta -- For family indexes, the tycon in -- in ds_tys is the *family* tycon - -- in ds_tc is the *representation* tycon + -- in ds_tc, ds_tc_args is the *representation* tycon -- For non-family tycons, both are the same -- ds_newtype = True <=> Newtype deriving @@ -253,7 +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. %************************************************************************ %* * @@ -266,10 +275,11 @@ 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 @@ -278,22 +288,22 @@ tcDeriving 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) + ; (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 @@ -301,13 +311,13 @@ 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 @@ -326,9 +336,10 @@ renameDeriv is_boot gen_binds insts ; let aux_names = map unLoc (collectHsValBinders rn_aux_lhs) ; bindLocalNames aux_names $ - 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) } } + 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)) } } where (inst_infos, deriv_aux_binds) = unzip insts @@ -339,16 +350,17 @@ 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 { iSpec = inst, iBinds = NewTypeDerived co }) + = return (InstInfo { iSpec = inst, iBinds = NewTypeDerived co }, emptyFVs) - 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 @@ -564,15 +576,12 @@ 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 = failWithTc (derivingThingErr cls cls_tys tc_app @@ -629,18 +638,28 @@ famInstNotFound tycon tys %************************************************************************ \begin{code} -mkDataTypeEqn :: InstOrigin -> Bool -> [Var] -> Class -> [Type] - -> TyCon -> [Type] -> TyCon -> [Type] -> Maybe ThetaType - -> TcRn 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 - = case checkSideConditions mayDeriveDataTypeable cls cls_tys rep_tc of - -- NB: pass the *representation* tycon to checkSideConditions - 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 + | 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 @@ -654,34 +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 - -- 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] - - 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_tc = rep_tc - , ds_theta = mtheta `orElse` all_constraints + , ds_cls = cls, ds_tys = inst_tys + , ds_tc = rep_tc, ds_tc_args = rep_tc_args + , ds_theta = mtheta `orElse` inferred_constraints , ds_newtype = False } ; 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 @@ -705,9 +709,66 @@ mk_typeable_eqn orig tvs cls tycon tc_args rep_tc _rep_tc_args mtheta ; loc <- getSrcSpanM ; return (Right $ DS { ds_loc = loc, ds_orig = orig, ds_name = dfun_name, ds_tvs = [] - , ds_cls = cls, ds_tys = [mkTyConApp tycon []], ds_tc = rep_tc + , ds_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 @@ -720,10 +781,10 @@ 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 +checkSideConditions :: DynFlags -> Class -> [TcType] -> TyCon -> DerivStatus +checkSideConditions dflags cls cls_tys rep_tc | Just cond <- sideConditions cls - = case (cond (mayDeriveDataTypeable, rep_tc)) of + = 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 ) @@ -736,21 +797,29 @@ 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 == 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) + | 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 @@ -771,15 +840,21 @@ 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)") + + 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` @@ -794,8 +869,7 @@ cond_noUnliftedArgs (_, tc) 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") + why = badCon (head bad_cons) (ptext (sLit "has arguments of unlifted type")) cond_isEnumeration :: Condition cond_isEnumeration (_, rep_tc) @@ -831,17 +905,59 @@ 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 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 - why = ptext (sLit "You need -XDeriveDataTypeable to derive an instance for this class") + 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 -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 @@ -852,6 +968,9 @@ new_dfun_name clas tycon -- Just a simple wrapper ; 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] @@ -886,11 +1005,11 @@ 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 EarlyDerivSpec -mkNewTypeEqn orig mayDeriveDataTypeable newtype_deriving tvs +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) @@ -899,23 +1018,25 @@ mkNewTypeEqn orig mayDeriveDataTypeable newtype_deriving tvs ; loc <- getSrcSpanM ; let spec = DS { ds_loc = loc, ds_orig = orig , ds_name = dfun_name, ds_tvs = varSetElems dfun_tvs - , ds_cls = cls, ds_tys = inst_tys, ds_tc = rep_tycon + , 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 Right spec else Left spec) } + | isJust mtheta = go_for_it -- Do not check side conditions for standalone deriving | 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 + = 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 - check_conditions = checkSideConditions mayDeriveDataTypeable cls cls_tys rep_tycon - bale_out msg = failWithTc (derivingThingErr cls cls_tys inst_ty msg) + 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") @@ -952,7 +1073,7 @@ mkNewTypeEqn orig mayDeriveDataTypeable newtype_deriving tvs 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 + -- 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 @@ -995,29 +1116,20 @@ mkNewTypeEqn orig mayDeriveDataTypeable newtype_deriving tvs ------------------------------------------------------------------- -- Figuring out whether we can only do this newtype-deriving thing - right_arity = length cls_tys + 1 == classArity cls + can_derive_via_isomorphism + = not (non_iso_class cls) + && arity_ok + && eta_ok + && ats_ok +-- && not (isRecursiveTyCon tycon) -- Note [Recursive newtypes] - -- Never derive Read,Show,Typeable,Data this way + -- Never derive Read,Show,Typeable,Data by isomorphism 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 - && 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 = 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 = nt_eta_arity <= length rep_tc_args @@ -1028,19 +1140,36 @@ mkNewTypeEqn orig mayDeriveDataTypeable newtype_deriving tvs -- 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 - ] + 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. + %************************************************************************ %* * @@ -1093,7 +1222,7 @@ 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 $ @@ -1131,11 +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 @@ -1224,28 +1350,43 @@ 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 }, []) | otherwise - = do { let loc = getSrcSpan (ds_name spec) - inst = mkInstance1 oflag spec - clas = ds_cls spec - rep_tycon = ds_tc spec + = do { let loc = getSrcSpan (ds_name spec) + inst = mkInstance oflag (ds_theta spec) spec + clas = ds_cls spec -- In case of a family instance, we need to use the representation -- tycon (after all, it has the data constructors) ; fix_env <- getFixityEnv ; let (meth_binds, aux_binds) = genDerivBinds loc fix_env clas rep_tycon - - -- Build the InstInfo - ; return (InstInfo { iSpec = inst, - iBinds = VanillaInst meth_binds [] }, - aux_binds) + 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 + 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 @@ -1266,6 +1407,9 @@ 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}