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
-- 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, 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
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
; 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))
+ ; when (not (null inst_info)) $
+ dumpDerivingInfo (ddump_deriving 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
- = vcat (map pprInstInfoDetails inst_infos) $$ ppr extra_binds
+ = hang (ptext (sLit "Derived instances"))
+ 2 (vcat (map (\i -> pprInstInfoDetails i $$ text "") inst_infos)
+ $$ ppr extra_binds)
renameDeriv :: Bool -> LHsBinds RdrName
-> [(InstInfo RdrName, DerivAuxBinds)]
-- 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 = collectHsValBinders rn_aux_lhs
-
- ; bindLocalNames aux_names $
- do { (rn_aux, dus_aux) <- rnTopBindsRHS (mkNameSet aux_names) rn_aux_lhs
+ ; 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)) } }
, mkFVs (map dataConName (tyConDataCons tc)))
-- See Note [Newtype deriving and unused constructors]
- rn_inst_info (InstInfo { iSpec = inst, iBinds = VanillaInst binds sigs standalone_deriv })
+ 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
; let binds' = VanillaInst rn_binds [] standalone_deriv
- ; return (InstInfo { iSpec = inst, iBinds = binds' }, fvs) }
+ ; return (inst_info { iBinds = binds' }, fvs) }
where
(tyvars,_, clas,_) = instanceHead inst
clas_nm = className clas
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) <- checkValidInstance deriv_ty tvs theta tau
+ 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) }
-- Type families can't be partially applied
-- e.g. newtype instance T Int a = MkT [a] deriving( Monad )
-- Note [Deriving, type families, and partial applications]
- ; checkTc (not (isOpenTyCon tc) || n_args_to_drop == 0)
+ ; checkTc (not (isFamilyTyCon tc) || n_args_to_drop == 0)
(typeFamilyPapErr tc cls cls_tys inst_ty)
; mkEqnHelp DerivOrigin (varSetElems univ_tvs) cls cls_tys inst_ty Nothing } }
... etc ...
\begin{code}
-mkEqnHelp :: InstOrigin -> [TyVar] -> Class -> [Type] -> Type
+mkEqnHelp :: CtOrigin -> [TyVar] -> Class -> [Type] -> Type
-> DerivContext -- Just => context supplied (standalone deriving)
-- Nothing => context inferred (deriving on data decl)
-> TcRn EarlyDerivSpec
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)
-
- ; 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 }
+ = mk_alg_eqn tycon tc_args
| otherwise
= 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
+mkDataTypeEqn :: CtOrigin
-> DynFlags
-> [Var] -- Universally quantified type variables in the instance
-> Class -- Class for which we need to derive an instance
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] -> DerivContext
- -> 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 inst_tys = [mkTyConApp tycon tc_args]
; 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)
; 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_tc_args = rep_tc_args
+ , 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
get_constrained_tys :: [Type] -> [Type]
get_constrained_tys tys
- | is_functor_like = concatMap (deepSubtypesContaining last_tv) tys
+ | is_functor_like = concatMap (deepSubtypesContaining last_tv) tys
| otherwise = tys
rep_tc_tvs = tyConTyVars rep_tc
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")
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
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") $$ y)
- -- Both fail
+ -- Both fail
andCond :: Condition -> Condition -> Condition
andCond c1 c2 tc = case c1 tc of
cond_stdOK (Just _) _
= Nothing -- Don't check these conservative conditions for
-- standalone deriving; just generate the code
+ -- and let the typechecker handle the result
cond_stdOK Nothing (_, rep_tc)
- | null data_cons = Just (no_cons_why $$ suggestion)
+ | null data_cons = Just (no_cons_why rep_tc $$ suggestion)
| not (null con_whys) = Just (vcat con_whys $$ suggestion)
| otherwise = Nothing
where
suggestion = ptext (sLit "Possible fix: use a standalone deriving declaration instead")
data_cons = tyConDataCons rep_tc
- no_cons_why = quotes (pprSourceTyCon rep_tc) <+>
- ptext (sLit "has no data constructors")
-
con_whys = mapCatMaybes check_con data_cons
check_con :: DataCon -> Maybe SDoc
, all isTauTy (dataConOrigArgTys con) = Nothing
| otherwise = Just (badCon con (ptext (sLit "does not have a Haskell-98 type")))
+no_cons_why :: TyCon -> SDoc
+no_cons_why rep_tc = quotes (pprSourceTyCon rep_tc) <+>
+ ptext (sLit "has no data constructors")
+
cond_enumOrProduct :: Condition
cond_enumOrProduct = cond_isEnumeration `orCond`
(cond_isProduct `andCond` cond_noUnliftedArgs)
cond_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")
+ , ptext (sLit "(an enumeration consists of one or more nullary, non-GADT 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")
-
functorLikeClassKeys :: [Unique]
functorLikeClassKeys = [functorClassKey, foldableClassKey, traversableClassKey]
cond_functorOK :: Bool -> Condition
--- OK for Functor class
+-- 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
-cond_functorOK allowFunctions (dflags, rep_tc)
- | not (dopt Opt_DeriveFunctor dflags)
- = Just (ptext (sLit "You need -XDeriveFunctor to derive an instance for this class"))
+-- (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)
functions = ptext (sLit "contains function types")
wrong_arg = ptext (sLit "uses the type variable in an argument other than the last")
-checkFlag :: LanguageFlag -> Condition
+checkFlag :: ExtensionFlag -> Condition
checkFlag flag (dflags, _)
- | dopt flag dflags = Nothing
+ | xopt flag dflags = Nothing
| otherwise = Just why
where
why = ptext (sLit "You need -X") <> text flag_str
%************************************************************************
\begin{code}
-mkNewTypeEqn :: InstOrigin -> DynFlags -> [Var] -> Class
+mkNewTypeEqn :: CtOrigin -> DynFlags -> [Var] -> Class
-> [Type] -> TyCon -> [Type] -> TyCon -> [Type]
-> DerivContext
-> TcRn EarlyDerivSpec
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
| can_derive_via_isomorphism -> bale_out (non_std $$ suggest_nd) -- Try newtype deriving!
| otherwise -> bale_out non_std
where
- newtype_deriving = dopt Opt_GeneralizedNewtypeDeriving dflags
+ 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)
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
------------------------------------------------------------------
gen_soln (DS { ds_loc = loc, ds_orig = orig, ds_tvs = tyvars
, 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
+ addErrCtxt (derivInstCtxt the_pred) $
+ 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
- ; traceTc (text "TcDeriv" <+> (ppr deriv_rhs $$ ppr theta))
+ ; theta <- simplifyDeriv orig the_pred 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
+ where
+ the_pred = mkClassPred clas inst_tys
------------------------------------------------------------------
mkInstance :: OverlapFlag -> ThetaType -> DerivSpec -> Instance
genInst :: Bool -- True <=> standalone deriving
-> OverlapFlag
-> DerivSpec -> TcM (InstInfo RdrName, DerivAuxBinds)
-genInst standalone_deriv oflag spec
- | ds_newtype spec
- = return (InstInfo { iSpec = mkInstance oflag (ds_theta spec) spec
- , iBinds = NewTypeDerived co rep_tycon }, [])
+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 = 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
- binds = VanillaInst meth_binds [] standalone_deriv
- ; return (InstInfo { iSpec = inst, iBinds = 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
- rep_tycon = ds_tc spec
- rep_tc_args = ds_tc_args spec
+ inst_spec = mkInstance oflag theta spec
co1 = case tyConFamilyCoercion_maybe rep_tycon of
- Nothing -> IdCo
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
- Nothing -> IdCo -- The newtype is transparent; no need for a cast
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)])
standaloneCtxt ty = hang (ptext (sLit "In the stand-alone deriving instance for"))
2 (quotes (ppr ty))
-derivInstCtxt :: Class -> [Type] -> Message
-derivInstCtxt clas inst_tys
- = ptext (sLit "When deriving the instance for") <+> parens (pprClassPred clas inst_tys)
+derivInstCtxt :: PredType -> Message
+derivInstCtxt pred
+ = ptext (sLit "When deriving the instance for") <+> parens (ppr pred)
badDerivedPred :: PredType -> Message
badDerivedPred pred
projects / ghc-hetmet.git / blobdiff