, ds_theta :: ThetaType
, ds_cls :: Class
, ds_tys :: [Type]
+ , ds_tc :: TyCon
, ds_newtype :: Bool }
-- This spec implies a dfun declaration of the form
-- df :: forall tvs. theta => C tys
-- The Name is the name for the DFun we'll build
-- The tyvars bind all the variables in the theta
- -- For family indexes, the tycon is the *family* tycon
- -- (not the representation tycon)
+ -- For family indexes, the tycon in
+ -- in ds_tys is the *family* tycon
+ -- in ds_tc is the *representation* tycon
+ -- For non-family tycons, both are the same
-- ds_newtype = True <=> Newtype deriving
-- False <=> Vanilla deriving
= recoverM (return ([], emptyValBindsOut)) $
do { -- Fish the "deriving"-related information out of the TcEnv
-- And make the necessary "equations".
- ; early_specs <- makeDerivSpecs tycl_decls inst_decls deriv_decls
+ is_boot <- tcIsHsBoot
+ ; traceTc (text "tcDeriving" <+> ppr is_boot)
+ ; early_specs <- makeDerivSpecs is_boot tycl_decls inst_decls deriv_decls
; overlap_flag <- getOverlapFlag
; let (infer_specs, given_specs) = splitEithers early_specs
; insts2 <- mapM (genInst overlap_flag) final_specs
- ; is_boot <- tcIsHsBoot
-- Generate the generic to/from functions from each type declaration
; gen_binds <- mkGenericBinds is_boot
; (inst_info, rn_binds) <- renameDeriv is_boot gen_binds (insts1 ++ insts2)
| otherwise
= discardWarnings $ -- Discard warnings about unused bindings etc
- do { (rn_gen, dus_gen) <- setOptM Opt_PatternSignatures $ -- Type signatures in patterns
- -- are used in the generic binds
+ do { (rn_gen, dus_gen) <- setOptM Opt_ScopedTypeVariables $ -- Type signatures in patterns
+ -- are used in the generic binds
rnTopBinds (ValBindsIn gen_binds [])
; keepAliveSetTc (duDefs dus_gen) -- Mark these guys to be kept alive
; let aux_binds = listToBag $ map (genAuxBind loc) $
rm_dups [] $ concat deriv_aux_binds
; rn_aux_lhs <- rnTopBindsLHS emptyFsEnv (ValBindsIn aux_binds [])
- ; let aux_names = map unLoc (collectHsValBinders rn_aux_lhs)
+ ; let aux_names = map unLoc (collectHsValBinders rn_aux_lhs)
; bindLocalNames aux_names $
- do { (rn_aux, _dus) <- rnTopBindsRHS aux_names rn_aux_lhs
+ do { (rn_aux, _dus) <- rnTopBindsRHS (mkNameSet aux_names) rn_aux_lhs
; rn_inst_infos <- mapM rn_inst_info inst_infos
; return (rn_inst_infos, rn_aux `plusHsValBinds` rn_gen) } }
%* *
%************************************************************************
-@makeDerivSpecs@ fishes around to find the info about needed derived
-instances. Complicating factors:
-\begin{itemize}
-\item
-We can only derive @Enum@ if the data type is an enumeration
-type (all nullary data constructors).
-
-\item
-We can only derive @Ix@ if the data type is an enumeration {\em
-or} has just one data constructor (e.g., tuples).
-\end{itemize}
-
-[See Appendix~E in the Haskell~1.2 report.] This code here deals w/
-all those.
+@makeDerivSpecs@ fishes around to find the info about needed derived instances.
\begin{code}
-makeDerivSpecs :: [LTyClDecl Name]
+makeDerivSpecs :: Bool
+ -> [LTyClDecl Name]
-> [LInstDecl Name]
-> [LDerivDecl Name]
-> TcM [EarlyDerivSpec]
-makeDerivSpecs tycl_decls inst_decls deriv_decls
- = do { eqns1 <- mapAndRecoverM deriveTyData $
- extractTyDataPreds tycl_decls ++
- [ pd -- traverse assoc data families
- | L _ (InstDecl _ _ _ ats) <- inst_decls
- , pd <- extractTyDataPreds ats ]
+makeDerivSpecs is_boot tycl_decls inst_decls deriv_decls
+ | is_boot -- No 'deriving' at all in hs-boot files
+ = do { mapM_ add_deriv_err deriv_locs
+ ; return [] }
+ | otherwise
+ = do { eqns1 <- mapAndRecoverM deriveTyData all_tydata
; eqns2 <- mapAndRecoverM deriveStandalone deriv_decls
- ; return (catMaybes (eqns1 ++ eqns2)) }
+ ; return (eqns1 ++ eqns2) }
where
- extractTyDataPreds decls =
- [(p, d) | d@(L _ (TyData {tcdDerivs = Just preds})) <- decls, p <- preds]
+ extractTyDataPreds decls
+ = [(p, d) | d@(L _ (TyData {tcdDerivs = Just preds})) <- decls, p <- preds]
+
+ all_tydata :: [(LHsType Name, LTyClDecl Name)]
+ -- Derived predicate paired with its data type declaration
+ all_tydata = extractTyDataPreds tycl_decls ++
+ [ pd -- Traverse assoc data families
+ | L _ (InstDecl _ _ _ ats) <- inst_decls
+ , pd <- extractTyDataPreds ats ]
+ deriv_locs = map (getLoc . snd) all_tydata
+ ++ map getLoc deriv_decls
+
+ add_deriv_err loc = setSrcSpan loc $
+ addErr (hang (ptext (sLit "Deriving not permitted in hs-boot file"))
+ 2 (ptext (sLit "Use an instance declaration instead")))
------------------------------------------------------------------
-deriveStandalone :: LDerivDecl Name -> TcM (Maybe EarlyDerivSpec)
+deriveStandalone :: LDerivDecl Name -> TcM EarlyDerivSpec
-- Standalone deriving declarations
--- e.g. deriving instance show a => Show (T a)
+-- e.g. deriving instance Show a => Show (T a)
-- Rather like tcLocalInstDecl
deriveStandalone (L loc (DerivDecl deriv_ty))
= setSrcSpan loc $
(Just theta) }
------------------------------------------------------------------
-deriveTyData :: (LHsType Name, LTyClDecl Name) -> TcM (Maybe EarlyDerivSpec)
+deriveTyData :: (LHsType Name, LTyClDecl Name) -> TcM EarlyDerivSpec
deriveTyData (L loc deriv_pred, L _ decl@(TyData { tcdLName = L _ tycon_name,
tcdTyVars = tv_names,
tcdTyPats = ty_pats }))
= setSrcSpan loc $ -- Use the location of the 'deriving' item
tcAddDeclCtxt decl $
- do { let hs_ty_args = ty_pats `orElse` map (nlHsTyVar . hsLTyVarName) tv_names
- hs_app = nlHsTyConApp tycon_name hs_ty_args
- -- We get kinding info for the tyvars by typechecking (T a b)
- -- Hence forming a tycon application and then dis-assembling it
- ; (tvs, tc_app) <- tcHsQuantifiedType tv_names hs_app
+ do { (tvs, tc, tc_args) <- get_lhs ty_pats
; tcExtendTyVarEnv tvs $ -- Deriving preds may (now) mention
-- the type variables for the type constructor
+
do { (deriv_tvs, cls, cls_tys) <- tcHsDeriv deriv_pred
-- The "deriv_pred" is a LHsType to take account of the fact that for
-- newtype deriving we allow deriving (forall a. C [a]).
- ; mkEqnHelp DerivOrigin (tvs++deriv_tvs) cls cls_tys tc_app Nothing } }
+
+ -- Given data T a b c = ... deriving( C d ),
+ -- we want to drop type variables from T so that (C d (T a)) is well-kinded
+ ; let cls_tyvars = classTyVars cls
+ kind = tyVarKind (last cls_tyvars)
+ (arg_kinds, _) = splitKindFunTys kind
+ n_args_to_drop = length arg_kinds
+ n_args_to_keep = tyConArity tc - n_args_to_drop
+ inst_ty = mkTyConApp tc (take n_args_to_keep tc_args)
+ inst_ty_kind = typeKind inst_ty
+
+ -- 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)
+
+ -- 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)
+ (typeFamilyPapErr tc cls cls_tys inst_ty)
+
+ ; mkEqnHelp DerivOrigin (tvs++deriv_tvs) cls cls_tys inst_ty Nothing } }
+ where
+ -- Tiresomely we must figure out the "lhs", which is awkward for type families
+ -- E.g. data T a b = .. deriving( Eq )
+ -- Here, the lhs is (T a b)
+ -- data instance TF Int b = ... deriving( Eq )
+ -- Here, the lhs is (TF Int b)
+ -- But if we just look up the tycon_name, we get is the *family*
+ -- tycon, but not pattern types -- they are in the *rep* tycon.
+ get_lhs Nothing = do { tc <- tcLookupTyCon tycon_name
+ ; let tvs = tyConTyVars tc
+ ; return (tvs, tc, mkTyVarTys tvs) }
+ get_lhs (Just pats) = do { let hs_app = nlHsTyConApp tycon_name pats
+ ; (tvs, tc_app) <- tcHsQuantifiedType tv_names hs_app
+ ; let (tc, tc_args) = tcSplitTyConApp tc_app
+ ; return (tvs, tc, tc_args) }
deriveTyData _other
= panic "derivTyData" -- Caller ensures that only TyData can happen
mkEqnHelp :: InstOrigin -> [TyVar] -> Class -> [Type] -> Type
-> Maybe ThetaType -- Just => context supplied (standalone deriving)
-- Nothing => context inferred (deriving on data decl)
- -> TcRn (Maybe EarlyDerivSpec)
+ -> TcRn EarlyDerivSpec
+-- Make the EarlyDerivSpec for an instance
+-- forall tvs. theta => cls (tys ++ [ty])
+-- where the 'theta' is optional (that's the Maybe part)
+-- Assumes that this declaration is well-kinded
+
mkEqnHelp orig tvs cls cls_tys tc_app mtheta
| Just (tycon, tc_args) <- tcSplitTyConApp_maybe tc_app
, isAlgTyCon tycon -- Check for functions, primitive types etc
-- 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.
- -- By this time we know that the thing is algebraic
- -- because we've called checkInstHead in derivingStandalone
; 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))
tvs cls cls_tys
tycon tc_args rep_tc rep_tc_args mtheta }
| otherwise
- = baleOut (derivingThingErr cls cls_tys tc_app
- (ptext (sLit "The last argument of the instance must be a data or newtype application")))
-
-baleOut :: Message -> TcM (Maybe a)
-baleOut err = do { addErrTc err; return Nothing }
+ = failWithTc (derivingThingErr cls cls_tys tc_app
+ (ptext (sLit "The last argument of the instance must be a data or newtype application")))
\end{code}
Note [Looking up family instances for deriving]
famInstNotFound :: TyCon -> [Type] -> TcM a
famInstNotFound tycon tys
= failWithTc (ptext (sLit "No family instance for")
- <+> quotes (pprTypeApp tycon (ppr tycon) tys))
+ <+> quotes (pprTypeApp tycon tys))
\end{code}
\begin{code}
mkDataTypeEqn :: InstOrigin -> Bool -> [Var] -> Class -> [Type]
-> TyCon -> [Type] -> TyCon -> [Type] -> Maybe ThetaType
- -> TcRn (Maybe EarlyDerivSpec) -- Return 'Nothing' if error
+ -> TcRn EarlyDerivSpec -- Return 'Nothing' if error
mkDataTypeEqn orig mayDeriveDataTypeable tvs cls cls_tys
tycon tc_args rep_tc rep_tc_args mtheta
- | Just err <- checkSideConditions mayDeriveDataTypeable cls cls_tys rep_tc
+ = case checkSideConditions mayDeriveDataTypeable cls cls_tys rep_tc of
-- NB: pass the *representation* tycon to checkSideConditions
- = baleOut (derivingThingErr cls cls_tys (mkTyConApp tycon tc_args) err)
-
- | otherwise
- = ASSERT( null cls_tys )
- mk_data_eqn orig tvs cls tycon tc_args rep_tc rep_tc_args mtheta
+ CanDerive -> mk_data_eqn orig tvs cls tycon tc_args rep_tc rep_tc_args mtheta
+ NonDerivableClass -> bale_out (nonStdErr cls)
+ DerivableClassError msg -> bale_out msg
+ where
+ bale_out msg = failWithTc (derivingThingErr cls cls_tys (mkTyConApp tycon tc_args) msg)
mk_data_eqn, mk_typeable_eqn
:: InstOrigin -> [TyVar] -> Class
-> TyCon -> [TcType] -> TyCon -> [TcType] -> Maybe ThetaType
- -> TcM (Maybe EarlyDerivSpec)
+ -> TcM EarlyDerivSpec
mk_data_eqn orig tvs cls tycon tc_args rep_tc rep_tc_args mtheta
| getName cls `elem` typeableClassNames
= mk_typeable_eqn orig tvs cls tycon tc_args rep_tc rep_tc_args mtheta
| data_con <- tyConDataCons rep_tc,
arg_ty <- ASSERT( isVanillaDataCon data_con )
dataConInstOrigArgTys data_con rep_tc_args,
- not (isUnLiftedType arg_ty) ] -- No constraints for unlifted types?
+ not (isUnLiftedType arg_ty) ]
+ -- No constraints for unlifted types
+ -- Where they are legal we generate specilised function calls
-- See Note [Superclasses of derived instance]
sc_constraints = substTheta (zipOpenTvSubst (classTyVars cls) inst_tys)
(classSCTheta cls)
- inst_tys = [mkTyConApp tycon tc_args]
+ inst_tys = [mkTyConApp tycon tc_args]
stupid_subst = zipTopTvSubst (tyConTyVars rep_tc) rep_tc_args
stupid_constraints = substTheta stupid_subst (tyConStupidTheta rep_tc)
spec = DS { ds_loc = loc, ds_orig = orig
, ds_name = dfun_name, ds_tvs = tvs
- , ds_cls = cls, ds_tys = inst_tys
+ , ds_cls = cls, ds_tys = inst_tys, ds_tc = rep_tc
, ds_theta = mtheta `orElse` all_constraints
, ds_newtype = False }
- ; return (if isJust mtheta then Just (Right spec) -- Specified context
- else Just (Left spec)) } -- Infer context
+ ; return (if isJust mtheta then Right spec -- Specified context
+ else Left spec) } -- Infer context
mk_typeable_eqn orig tvs cls tycon tc_args rep_tc _rep_tc_args mtheta
-- The Typeable class is special in several ways
<> int (tyConArity tycon) <+> ppr tycon <> rparen)
; dfun_name <- new_dfun_name cls tycon
; loc <- getSrcSpanM
- ; return (Just $ Right $
+ ; return (Right $
DS { ds_loc = loc, ds_orig = orig, ds_name = dfun_name, ds_tvs = []
- , ds_cls = cls, ds_tys = [mkTyConApp tycon []]
+ , ds_cls = cls, ds_tys = [mkTyConApp tycon []], ds_tc = rep_tc
, ds_theta = mtheta `orElse` [], ds_newtype = False }) }
------------------------------------------------------------------
-- the data constructors - but we need to be careful to fall back to the
-- family tycon (with indexes) in error messages.
-checkSideConditions :: Bool -> Class -> [TcType] -> TyCon -> Maybe SDoc
+data DerivStatus = CanDerive
+ | NonDerivableClass
+ | DerivableClassError SDoc
+
+checkSideConditions :: Bool -> Class -> [TcType] -> TyCon -> DerivStatus
checkSideConditions mayDeriveDataTypeable cls cls_tys rep_tc
| notNull cls_tys
- = Just ty_args_why -- e.g. deriving( Foo s )
+ = DerivableClassError ty_args_why -- e.g. deriving( Foo s )
| otherwise
= case sideConditions cls of
- Just cond -> cond (mayDeriveDataTypeable, rep_tc)
- Nothing -> Just non_std_why
+ Nothing -> NonDerivableClass
+ Just cond -> case (cond (mayDeriveDataTypeable, rep_tc)) of
+ Nothing -> CanDerive
+ Just err -> DerivableClassError err
where
ty_args_why = quotes (ppr (mkClassPred cls cls_tys)) <+> ptext (sLit "is not a class")
- non_std_why = quotes (ppr cls) <+> ptext (sLit "is not a derivable class")
+
+nonStdErr :: Class -> SDoc
+nonStdErr cls = quotes (ppr cls) <+> ptext (sLit "is not a derivable class")
sideConditions :: Class -> Maybe Condition
sideConditions cls
- | cls_key == eqClassKey = Just cond_std
- | cls_key == ordClassKey = Just cond_std
- | cls_key == readClassKey = Just cond_std
- | cls_key == showClassKey = Just cond_std
- | cls_key == enumClassKey = Just (cond_std `andCond` cond_isEnumeration)
- | cls_key == ixClassKey = Just (cond_std `andCond` (cond_isEnumeration `orCond` cond_isProduct))
- | cls_key == boundedClassKey = Just (cond_std `andCond` (cond_isEnumeration `orCond` cond_isProduct))
- | cls_key == dataClassKey = Just (cond_mayDeriveDataTypeable `andCond` cond_std)
+ | cls_key == eqClassKey = Just cond_std
+ | cls_key == ordClassKey = Just cond_std
+ | cls_key == showClassKey = Just cond_std
+ | cls_key == readClassKey = Just (cond_std `andCond` cond_noUnliftedArgs)
+ | cls_key == enumClassKey = Just (cond_std `andCond` cond_isEnumeration)
+ | cls_key == ixClassKey = Just (cond_std `andCond` cond_enumOrProduct)
+ | cls_key == boundedClassKey = Just (cond_std `andCond` cond_enumOrProduct)
+ | cls_key == dataClassKey = Just (cond_mayDeriveDataTypeable `andCond` cond_std `andCond` cond_noUnliftedArgs)
| getName cls `elem` typeableClassNames = Just (cond_mayDeriveDataTypeable `andCond` cond_typeableOK)
| otherwise = Nothing
where
existential_why = quotes (pprSourceTyCon rep_tc) <+>
ptext (sLit "has non-Haskell-98 constructor(s)")
+cond_enumOrProduct :: Condition
+cond_enumOrProduct = cond_isEnumeration `orCond`
+ (cond_isProduct `andCond` cond_noUnliftedArgs)
+
+cond_noUnliftedArgs :: Condition
+-- For some classes (eg Eq, Ord) we allow unlifted arg types
+-- by generating specilaised code. For others (eg Data) we don't.
+cond_noUnliftedArgs (_, tc)
+ | null bad_cons = Nothing
+ | otherwise = Just why
+ where
+ bad_cons = [ con | con <- tyConDataCons tc
+ , any isUnLiftedType (dataConOrigArgTys con) ]
+ why = ptext (sLit "Constructor") <+> quotes (ppr (head bad_cons))
+ <+> ptext (sLit "has arguments of unlifted type")
+
cond_isEnumeration :: Condition
cond_isEnumeration (_, rep_tc)
| isEnumerationTyCon rep_tc = Nothing
mkNewTypeEqn :: InstOrigin -> Bool -> Bool -> [Var] -> Class
-> [Type] -> TyCon -> [Type] -> TyCon -> [Type]
-> Maybe ThetaType
- -> TcRn (Maybe EarlyDerivSpec)
+ -> TcRn EarlyDerivSpec
mkNewTypeEqn orig mayDeriveDataTypeable newtype_deriving tvs
cls cls_tys tycon tc_args rep_tycon rep_tc_args mtheta
| can_derive_via_isomorphism && (newtype_deriving || std_class_via_iso cls)
; dfun_name <- new_dfun_name cls tycon
; loc <- getSrcSpanM
; let spec = DS { ds_loc = loc, ds_orig = orig
- , ds_name = dfun_name, ds_tvs = dict_tvs
- , ds_cls = cls, ds_tys = inst_tys
+ , ds_name = dfun_name, ds_tvs = varSetElems dfun_tvs
+ , ds_cls = cls, ds_tys = inst_tys, ds_tc = rep_tycon
, ds_theta = mtheta `orElse` all_preds
, ds_newtype = True }
- ; return (if isJust mtheta then Just (Right spec)
- else Just (Left spec)) }
+ ; return (if isJust mtheta then Right spec
+ else Left spec) }
- | isNothing mb_std_err -- Use the standard H98 method
- = mk_data_eqn orig tvs cls tycon tc_args rep_tycon rep_tc_args mtheta
-
- -- Otherwise we can't derive
- | newtype_deriving = baleOut cant_derive_err -- Too hard
- | otherwise = baleOut std_err -- Just complain about being a non-std instance
+ | otherwise
+ = case check_conditions of
+ CanDerive -> mk_data_eqn orig tvs cls tycon tc_args rep_tycon rep_tc_args mtheta
+ -- Use the standard H98 method
+ DerivableClassError msg -> bale_out msg -- Error with standard class
+ NonDerivableClass -- Must use newtype deriving
+ | newtype_deriving -> bale_out cant_derive_err -- Too hard, even with newtype deriving
+ | otherwise -> bale_out non_std_err -- Try newtype deriving!
where
- mb_std_err = checkSideConditions mayDeriveDataTypeable cls cls_tys rep_tycon
- std_err = derivingThingErr cls cls_tys tc_app $
- vcat [fromJust mb_std_err,
- ptext (sLit "Try -XGeneralizedNewtypeDeriving for GHC's newtype-deriving extension")]
+ check_conditions = checkSideConditions mayDeriveDataTypeable cls cls_tys rep_tycon
+ bale_out msg = failWithTc (derivingThingErr cls cls_tys inst_ty msg)
+
+ non_std_err = nonStdErr cls $$
+ ptext (sLit "Try -XGeneralizedNewtypeDeriving for GHC's newtype-deriving extension")
-- Here is the plan for newtype derivings. We see
-- newtype T a1...an = MkT (t ak+1...an) deriving (.., C s1 .. sm, ...)
-- with the last parameter missing
-- (T a1 .. ak) matches the kind of C's last argument
-- (and hence so does t)
+ -- The latter kind-check has been done by deriveTyData already,
+ -- and tc_args are already trimmed
--
-- We generate the instance
-- instance forall ({a1..ak} u fvs(s1..sm)).
-- We generate the instance
-- instance Monad (ST s) => Monad (T s) where
- cls_tyvars = classTyVars cls
- kind = tyVarKind (last cls_tyvars)
- -- Kind of the thing we want to instance
- -- e.g. argument kind of Monad, *->*
-
- (arg_kinds, _) = splitKindFunTys kind
- n_args_to_drop = length arg_kinds
- -- Want to drop 1 arg from (T s a) and (ST s a)
- -- to get instance Monad (ST s) => Monad (T s)
+ nt_eta_arity = length (fst (newTyConEtadRhs rep_tycon))
+ -- For newtype T a b = MkT (S a a b), the TyCon machinery already
+ -- eta-reduces the represenation type, so we know that
+ -- T a ~ S a a
+ -- That's convenient here, because we may have to apply
+ -- it to fewer than its original complement of arguments
-- Note [Newtype representation]
-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-- newtype A = MkA B deriving( Num )
-- We want the Num instance of B, *not* the Num instance of Int,
-- when making the Num instance of A!
- rep_ty = newTyConInstRhs rep_tycon rep_tc_args
- (rep_fn, rep_ty_args) = tcSplitAppTys rep_ty
-
- n_tyargs_to_keep = tyConArity tycon - n_args_to_drop
- dropped_tc_args = drop n_tyargs_to_keep tc_args
- dropped_tvs = tyVarsOfTypes dropped_tc_args
-
- n_args_to_keep = length rep_ty_args - n_args_to_drop
- args_to_drop = drop n_args_to_keep rep_ty_args
- args_to_keep = take n_args_to_keep rep_ty_args
-
- rep_fn' = mkAppTys rep_fn args_to_keep
- rep_tys = cls_tys ++ [rep_fn']
- rep_pred = mkClassPred cls rep_tys
+ rep_inst_ty = newTyConInstRhs rep_tycon rep_tc_args
+ rep_tys = cls_tys ++ [rep_inst_ty]
+ rep_pred = mkClassPred cls rep_tys
-- rep_pred is the representation dictionary, from where
-- we are gong to get all the methods for the newtype
-- dictionary
- tc_app = mkTyConApp tycon (take n_tyargs_to_keep tc_args)
-- Next we figure out what superclass dictionaries to use
-- See Note [Newtype deriving superclasses] above
- inst_tys = cls_tys ++ [tc_app]
+ cls_tyvars = classTyVars cls
+ dfun_tvs = tyVarsOfTypes tc_args
+ inst_ty = mkTyConApp tycon tc_args
+ inst_tys = cls_tys ++ [inst_ty]
sc_theta = substTheta (zipOpenTvSubst cls_tyvars inst_tys)
(classSCTheta cls)
-- instance C T
-- rather than
-- instance C Int => C T
- dict_tvs = filterOut (`elemVarSet` dropped_tvs) tvs
all_preds = rep_pred : sc_theta -- NB: rep_pred comes first
-------------------------------------------------------------------
&& right_arity -- Well kinded;
-- eg not: newtype T ... deriving( ST )
-- because ST needs *2* type params
- && n_tyargs_to_keep >= 0 -- Type constructor has right kind:
- -- eg not: newtype T = T Int deriving( Monad )
- && n_args_to_keep >= 0 -- Rep type has right kind:
- -- eg not: newtype T a = T Int deriving( Monad )
&& eta_ok -- Eta reduction works
&& not (isRecursiveTyCon tycon) -- Does not work for recursive tycons:
-- newtype A = MkA [A]
-- recursive newtypes too
-- Check that eta reduction is OK
- eta_ok = (args_to_drop `tcEqTypes` dropped_tc_args)
- -- (a) the dropped-off args are identical in the source and rep type
+ eta_ok = (nt_eta_arity <= length rep_tc_args)
+ -- (a) 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.
- && (tyVarsOfType rep_fn' `disjointVarSet` dropped_tvs)
- -- (b) the remaining type args do not mention any of the dropped
- -- type variables
-
- && (tyVarsOfTypes cls_tys `disjointVarSet` dropped_tvs)
+ && (tyVarsOfTypes cls_tys `subVarSet` dfun_tvs)
-- (c) the type class args do not mention any of the dropped type
-- variables
-
- && all isTyVarTy dropped_tc_args
- -- (d) in case of newtype family instances, the eta-dropped
- -- arguments must be type variables (not more complex indexes)
-
- cant_derive_err = derivingThingErr cls cls_tys tc_app
- (vcat [ptext (sLit "even with cunning newtype deriving:"),
- if isRecursiveTyCon tycon then
- ptext (sLit "the newtype may be recursive")
- else empty,
- if not right_arity then
- quotes (ppr (mkClassPred cls cls_tys)) <+> ptext (sLit "does not have arity 1")
- else empty,
- if not (n_tyargs_to_keep >= 0) then
- ptext (sLit "the type constructor has wrong kind")
- else if not (n_args_to_keep >= 0) then
- ptext (sLit "the representation type has wrong kind")
- else if not eta_ok then
- ptext (sLit "the eta-reduction property does not hold")
- else empty
- ])
+ -- 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
+ ]
\end{code}
genInst :: OverlapFlag -> DerivSpec -> TcM (InstInfo RdrName, DerivAuxBinds)
genInst oflag spec
| ds_newtype spec
- = return (InstInfo { iSpec = mkInstance1 oflag spec
+ = return (InstInfo { iSpec = mkInstance1 oflag spec
, iBinds = NewTypeDerived }, [])
| otherwise
- = do { let loc = getSrcSpan (ds_name spec)
- inst = mkInstance1 oflag spec
- (_,_,clas,[ty]) = instanceHead inst
- (visible_tycon, tyArgs) = tcSplitTyConApp ty
+ = do { let loc = getSrcSpan (ds_name spec)
+ inst = mkInstance1 oflag spec
+ clas = ds_cls spec
+ rep_tycon = ds_tc spec
-- In case of a family instance, we need to use the representation
-- tycon (after all, it has the data constructors)
- ; (tycon, _) <- tcLookupFamInstExact visible_tycon tyArgs
; fix_env <- getFixityEnv
- ; let (meth_binds, aux_binds) = genDerivBinds loc fix_env clas tycon
+ ; let (meth_binds, aux_binds) = genDerivBinds loc fix_env clas rep_tycon
-- Build the InstInfo
; return (InstInfo { iSpec = inst,
%************************************************************************
\begin{code}
+derivingKindErr :: TyCon -> Class -> [Type] -> Kind -> Message
+derivingKindErr tc cls cls_tys cls_kind
+ = hang (ptext (sLit "Cannot derive well-kinded instance of form")
+ <+> quotes (pprClassPred cls cls_tys <+> parens (ppr tc <+> ptext (sLit "..."))))
+ 2 (ptext (sLit "Class") <+> quotes (ppr cls)
+ <+> ptext (sLit "expects an argument of kind") <+> quotes (pprKind cls_kind))
+
+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"),
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