X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Ftypecheck%2FTcDeriv.lhs;h=1a212408a62dba6273d3f987a5422f5a36e009ed;hb=79a6f3fa318020567566f92740ba6b9eb542f73f;hp=44ea1fc4caa2e69adc898878b2f8ac117f867220;hpb=5f8d93baa07271687825458e01c187081bcb1ddc;p=ghc-hetmet.git diff --git a/compiler/typecheck/TcDeriv.lhs b/compiler/typecheck/TcDeriv.lhs index 44ea1fc..1a21240 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 @@ -75,6 +76,7 @@ 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 +84,7 @@ 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 @@ -339,8 +341,8 @@ 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 }) rn_inst_info (InstInfo { iSpec = inst, iBinds = VanillaInst binds sigs }) = -- Bring the right type variables into @@ -459,19 +461,34 @@ deriveTyData (L loc deriv_pred, L _ decl@(TyData { tcdLName = L _ tycon_name, (arg_kinds, _) = splitKindFunTys kind n_args_to_drop = length arg_kinds n_args_to_keep = tyConArity tc - n_args_to_drop - inst_ty = mkTyConApp tc (take n_args_to_keep tc_args) - inst_ty_kind = typeKind inst_ty - + 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 = ... deriving( Monad ) + -- 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 (tvs++deriv_tvs) cls cls_tys inst_ty Nothing } } + ; 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 ) @@ -490,8 +507,37 @@ deriveTyData (L loc deriv_pred, L _ decl@(TyData { tcdLName = L _ tycon_name, 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) @@ -630,14 +676,15 @@ 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_tc = rep_tc + , ds_cls = cls, ds_tys = inst_tys + , ds_tc = rep_tc, ds_tc_args = rep_tc_args , ds_theta = mtheta `orElse` all_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 @@ -661,7 +708,8 @@ 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 }) } ------------------------------------------------------------------ @@ -673,19 +721,17 @@ mk_typeable_eqn orig tvs cls tycon tc_args rep_tc _rep_tc_args mtheta -- family tycon (with indexes) in error messages. data DerivStatus = CanDerive - | NonDerivableClass - | DerivableClassError SDoc + | 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 - = DerivableClassError ty_args_why -- e.g. deriving( Foo s ) - | otherwise - = case sideConditions cls of - Nothing -> NonDerivableClass - Just cond -> case (cond (mayDeriveDataTypeable, rep_tc)) of - Nothing -> CanDerive - Just err -> DerivableClassError err + | 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") @@ -850,13 +896,15 @@ mkNewTypeEqn :: InstOrigin -> Bool -> Bool -> [Var] -> Class -> 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 = 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 @@ -909,7 +957,7 @@ 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 @@ -934,7 +982,7 @@ mkNewTypeEqn orig mayDeriveDataTypeable newtype_deriving tvs -- See Note [Newtype deriving superclasses] above cls_tyvars = classTyVars cls - dfun_tvs = tyVarsOfTypes tc_args + 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) @@ -963,33 +1011,17 @@ mkNewTypeEqn orig mayDeriveDataTypeable newtype_deriving tvs -- 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 +-- && not (isRecursiveTyCon tycon) -- Note [Recursive newtypes] -- Check that eta reduction is OK - eta_ok = (nt_eta_arity <= length rep_tc_args) - -- (a) the newtype can be eta-reduced to match the number + 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) -- And the [a] must not mention 'b'. That's all handled -- by nt_eta_rity. - && (tyVarsOfTypes cls_tys `subVarSet` dfun_tvs) - -- (c) the type class args do not mention any of the dropped type - -- variables - -- newtype T a b = ... deriving( Monad b ) - cant_derive_err = vcat [ptext (sLit "even with cunning newtype deriving:"), if isRecursiveTyCon tycon then ptext (sLit "the newtype may be recursive") @@ -1003,6 +1035,21 @@ mkNewTypeEqn orig mayDeriveDataTypeable newtype_deriving tvs ] \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. + %************************************************************************ %* * @@ -1055,7 +1102,7 @@ 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 $ @@ -1093,11 +1140,8 @@ 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 @@ -1189,14 +1233,13 @@ 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 - , 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 + inst = mkInstance oflag (ds_theta spec) 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) @@ -1208,6 +1251,23 @@ genInst oflag spec iBinds = VanillaInst meth_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 @@ -1246,6 +1306,12 @@ derivingKindErr tc cls cls_tys cls_kind 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])))