import Class
import Type
+import Coercion
import ErrUtils
import MkId
import DataCon
import Outputable
import FastString
import Bag
+
+import Control.Monad
\end{code}
%************************************************************************
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 in
+ -- For type families, 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
-- 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
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.
%************************************************************************
%* *
-> [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
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
-- 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 (mkNameSet 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
| 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 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 (inst_info { 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.
+
%************************************************************************
%* *
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
deriveStandalone (L loc (DerivDecl deriv_ty))
= setSrcSpan loc $
addErrCtxt (standaloneCtxt deriv_ty) $
- do { traceTc (text "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
+ do { traceTc "Standalone deriving decl for" (ppr deriv_ty)
+ ; (tvs, theta, cls, inst_tys) <- tcHsInstHead deriv_ty
+ ; traceTc "Standalone deriving;" $ vcat
+ [ text "tvs:" <+> ppr tvs
+ , text "theta:" <+> ppr theta
+ , text "cls:" <+> ppr cls
+ , text "tys:" <+> ppr inst_tys ]
+ ; checkValidInstance deriv_ty tvs theta cls inst_tys
-- C.f. TcInstDcls.tcLocalInstDecl1
; let cls_tys = take (length inst_tys - 1) inst_tys
inst_ty = last inst_tys
- ; traceTc (text "standalone deriving;"
- <+> text "class:" <+> ppr cls
- <+> text "class types:" <+> ppr cls_tys
- <+> 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) }
(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 )
- ; checkTc (not (isOpenTyCon tc) || n_args_to_drop == 0)
+ -- 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 (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 )
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 EarlyDerivSpec
-- Make the EarlyDerivSpec for an instance
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
- -- Be careful to test rep_tc here: in the case of families,
- -- we want to check the instance tycon, not the family tycon
-
- -- For standalone deriving (mtheta /= Nothing),
- -- check that all the data constructors are in scope.
- -- No need for this when deriving Typeable, becuase we don't need
- -- the constructors for that.
- ; rdr_env <- getGlobalRdrEnv
- ; let hidden_data_cons = isAbstractTyCon rep_tc || any not_in_scope (tyConDataCons rep_tc)
- not_in_scope dc = null (lookupGRE_Name rdr_env (dataConName dc))
- ; checkTc (isNothing mtheta ||
- not hidden_data_cons ||
- className cls `elem` typeableClassNames)
- (derivingHiddenErr tycon)
-
- ; mayDeriveDataTypeable <- doptM Opt_DeriveDataTypeable
- ; newtype_deriving <- doptM Opt_GeneralizedNewtypeDeriving
-
- ; if isDataTyCon rep_tc then
- mkDataTypeEqn orig mayDeriveDataTypeable tvs cls cls_tys
- tycon tc_args rep_tc rep_tc_args mtheta
- else
- mkNewTypeEqn orig mayDeriveDataTypeable newtype_deriving
- tvs cls cls_tys
- tycon tc_args rep_tc rep_tc_args mtheta }
+ = mk_alg_eqn tycon tc_args
| otherwise
- = failWithTc (derivingThingErr cls cls_tys tc_app
+ = 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}
-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.
+ where
+ bale_out msg = failWithTc (derivingThingErr False cls cls_tys tc_app msg)
-\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))
+ mk_alg_eqn tycon tc_args
+ | className cls `elem` typeableClassNames
+ = do { dflags <- getDOpts
+ ; case checkTypeableConditions (dflags, tycon) of
+ Just err -> bale_out err
+ Nothing -> mk_typeable_eqn orig tvs cls tycon tc_args mtheta }
+
+ | isDataFamilyTyCon tycon
+ , length tc_args /= tyConArity tycon
+ = bale_out (ptext (sLit "Unsaturated data family application"))
+
+ | otherwise
+ = 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
+
+ -- For standalone deriving (mtheta /= Nothing),
+ -- check that all the data constructors are in scope.
+ ; 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))
+ ; unless (isNothing mtheta || not hidden_data_cons)
+ (bale_out (derivingHiddenErr tycon))
+
+ ; dflags <- getDOpts
+ ; if isDataTyCon rep_tc then
+ mkDataTypeEqn orig dflags tvs cls cls_tys
+ tycon tc_args rep_tc rep_tc_args mtheta
+ else
+ mkNewTypeEqn orig dflags tvs cls cls_tys
+ tycon tc_args rep_tc rep_tc_args mtheta }
\end{code}
%************************************************************************
\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 :: 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
- = case checkSideConditions mayDeriveDataTypeable cls cls_tys rep_tc of
+ = case checkSideConditions dflags mtheta 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
+ CanDerive -> go_for_it
NonDerivableClass -> bale_out (nonStdErr cls)
DerivableClassError msg -> bale_out msg
where
- bale_out msg = failWithTc (derivingThingErr cls cls_tys (mkTyConApp tycon tc_args) msg)
+ 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 EarlyDerivSpec
+mk_data_eqn :: 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
-
- | 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 :: CtOrigin -> [TyVar] -> Class
+ -> TyCon -> [TcType] -> DerivContext
+ -> TcM EarlyDerivSpec
+mk_typeable_eqn orig tvs cls tycon tc_args mtheta
-- The Typeable class is special in several ways
-- data T a b = ... deriving( Typeable )
-- gives
= do { checkTc (cls `hasKey` typeableClassKey)
(ptext (sLit "Use deriving( Typeable ) on a data type declaration"))
; real_cls <- tcLookupClass (typeableClassNames !! tyConArity tycon)
- ; mk_typeable_eqn orig tvs real_cls tycon [] rep_tc [] (Just []) }
+ ; mk_typeable_eqn orig tvs real_cls tycon [] (Just []) }
| otherwise -- standaone deriving
= do { checkTc (null tc_args)
; 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 = tycon, ds_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
-- family tycon (with indexes) in error messages.
data DerivStatus = CanDerive
- | NonDerivableClass
- | DerivableClassError SDoc
-
-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
+ | 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")
+checkTypeableConditions :: Condition
+checkTypeableConditions = checkFlag Opt_DeriveDataTypeable `andCond` cond_typeableOK
+
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 == 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)
+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)
| 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
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)
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)
- | 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)
| 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
-- Currently: (a) args all of kind *
-- (b) 7 or fewer args
-cond_typeableOK (_, rep_tc)
- | tyConArity rep_tc > 7 = Just too_many
- | not (all (isSubArgTypeKind . tyVarKind) (tyConTyVars rep_tc))
- = Just bad_kind
- | isFamInstTyCon rep_tc = Just fam_inst -- no Typable for family insts
- | otherwise = Nothing
+cond_typeableOK (_, tc)
+ | tyConArity tc > 7 = Just too_many
+ | not (all (isSubArgTypeKind . tyVarKind) (tyConTyVars tc))
+ = Just bad_kind
+ | otherwise = Nothing
where
- too_many = quotes (pprSourceTyCon rep_tc) <+>
+ too_many = quotes (pprSourceTyCon tc) <+>
ptext (sLit "has too many arguments")
- bad_kind = quotes (pprSourceTyCon rep_tc) <+>
+ bad_kind = quotes (pprSourceTyCon tc) <+>
ptext (sLit "has arguments of kind other than `*'")
- 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 (_, rep_tc)
+ | 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]
%************************************************************************
\begin{code}
-mkNewTypeEqn :: InstOrigin -> Bool -> Bool -> [Var] -> Class
+mkNewTypeEqn :: CtOrigin -> DynFlags -> [Var] -> Class
-> [Type] -> TyCon -> [Type] -> TyCon -> [Type]
- -> Maybe ThetaType
+ -> DerivContext
-> 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)
- = 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 = 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) }
| 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 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 $$ suggest_nd)
+ | otherwise -> bale_out msg
NonDerivableClass -- Must use newtype deriving
- | newtype_deriving -> bale_out cant_derive_err -- Too hard, even with newtype deriving
- | otherwise -> bale_out non_std_err -- Try newtype deriving!
+ | newtype_deriving -> bale_out cant_derive_err -- Too hard, even with newtype deriving
+ | can_derive_via_isomorphism -> bale_out (non_std $$ suggest_nd) -- Try newtype deriving!
+ | otherwise -> bale_out non_std
where
- check_conditions = checkSideConditions mayDeriveDataTypeable cls cls_tys rep_tycon
- bale_out msg = failWithTc (derivingThingErr cls cls_tys inst_ty msg)
+ 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_err = nonStdErr cls $$
- ptext (sLit "Try -XGeneralizedNewtypeDeriving for GHC's newtype-deriving extension")
+ 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, ...)
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
-- 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)
-------------------------------------------------------------------
-- 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
- && 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 = (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")
- 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 [ 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.
+
%************************************************************************
%* *
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
------------------------------------------------------------------
| 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 $
, 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
-- 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
- | ds_newtype spec
- = return (InstInfo { iSpec = mkInstance1 oflag spec
- , iBinds = NewTypeDerived }, [])
+genInst :: Bool -- True <=> standalone deriving
+ -> OverlapFlag
+ -> DerivSpec -> TcM (InstInfo RdrName, DerivAuxBinds)
+genInst standalone_deriv oflag
+ spec@(DS { ds_tc = rep_tycon, ds_tc_args = rep_tc_args
+ , ds_theta = theta, ds_newtype = is_newtype
+ , ds_name = name, ds_cls = clas })
+ | is_newtype
+ = return (InstInfo { iSpec = inst_spec
+ , iBinds = NewTypeDerived co rep_tycon }, [])
| otherwise
- = 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)
- ; 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)
- }
+ = do { fix_env <- getFixityEnv
+ ; let loc = getSrcSpan name
+ (meth_binds, aux_binds) = genDerivBinds loc fix_env clas rep_tycon
+ -- In case of a family instance, we need to use the representation
+ -- tycon (after all, it has the data constructors)
+
+ ; return (InstInfo { iSpec = inst_spec
+ , iBinds = VanillaInst meth_binds [] standalone_deriv }
+ , aux_binds) }
+ where
+ inst_spec = mkInstance oflag theta 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
,(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}
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"),
- quotes (ppr pred)],
- nest 2 (parens why)]
+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
projects / ghc-hetmet.git / blobdiff