import Class
import Type
+import Coercion
import ErrUtils
import MkId
import DataCon
import Outputable
import FastString
import Bag
+
+import Control.Monad
\end{code}
%************************************************************************
, 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 tyvars bind all the variables in the theta
-- For family indexes, the tycon in
-- in ds_tys is the *family* tycon
- -- in ds_tc is the *representation* tycon
+ -- in ds_tc, ds_tc_args is the *representation* tycon
-- For non-family tycons, both are the same
-- ds_newtype = True <=> Newtype deriving
| otherwise = rm_dups (b:acc) bs
- rn_inst_info (InstInfo { iSpec = inst, iBinds = NewTypeDerived })
- = return (InstInfo { iSpec = inst, iBinds = NewTypeDerived })
+ rn_inst_info (InstInfo { iSpec = inst, iBinds = NewTypeDerived co })
+ = return (InstInfo { iSpec = inst, iBinds = NewTypeDerived co })
rn_inst_info (InstInfo { iSpec = inst, iBinds = VanillaInst binds sigs })
= -- Bring the right type variables into
className cls `elem` typeableClassNames)
(derivingHiddenErr tycon)
- ; mayDeriveDataTypeable <- doptM Opt_DeriveDataTypeable
- ; newtype_deriving <- doptM Opt_GeneralizedNewtypeDeriving
-
+ ; dflags <- getDOpts
; if isDataTyCon rep_tc then
- mkDataTypeEqn orig mayDeriveDataTypeable tvs cls cls_tys
+ mkDataTypeEqn orig dflags tvs cls cls_tys
tycon tc_args rep_tc rep_tc_args mtheta
else
- mkNewTypeEqn orig mayDeriveDataTypeable newtype_deriving
- tvs cls cls_tys
+ mkNewTypeEqn orig dflags tvs cls cls_tys
tycon tc_args rep_tc rep_tc_args mtheta }
| otherwise
= failWithTc (derivingThingErr cls cls_tys tc_app
%************************************************************************
\begin{code}
-mkDataTypeEqn :: InstOrigin -> Bool -> [Var] -> Class -> [Type]
- -> TyCon -> [Type] -> TyCon -> [Type] -> Maybe ThetaType
- -> TcRn EarlyDerivSpec -- Return 'Nothing' if error
-
-mkDataTypeEqn orig mayDeriveDataTypeable tvs cls cls_tys
+mkDataTypeEqn :: InstOrigin
+ -> DynFlags
+ -> [Var] -- Universally quantified type variables in the instance
+ -> Class -- Class for which we need to derive an instance
+ -> [Type] -- Other parameters to the class except the last
+ -> TyCon -- Type constructor for which the instance is requested (last parameter to the type class)
+ -> [Type] -- Parameters to the type constructor
+ -> TyCon -- rep of the above (for type families)
+ -> [Type] -- rep of the above
+ -> Maybe ThetaType -- Context of the instance, for standalone deriving
+ -> TcRn EarlyDerivSpec -- Return 'Nothing' if error
+
+mkDataTypeEqn orig dflags tvs cls cls_tys
tycon tc_args rep_tc rep_tc_args mtheta
- = case checkSideConditions mayDeriveDataTypeable cls cls_tys rep_tc of
+ = case checkSideConditions dflags cls cls_tys rep_tc of
-- NB: pass the *representation* tycon to checkSideConditions
CanDerive -> mk_data_eqn orig tvs cls tycon tc_args rep_tc rep_tc_args mtheta
NonDerivableClass -> bale_out (nonStdErr cls)
| otherwise
= do { dfun_name <- new_dfun_name cls tycon
; loc <- getSrcSpanM
- ; let ordinary_constraints
- = [ mkClassPred cls [arg_ty]
- | data_con <- tyConDataCons rep_tc,
- arg_ty <- ASSERT( isVanillaDataCon data_con )
- dataConInstOrigArgTys data_con rep_tc_args,
- not (isUnLiftedType arg_ty) ]
- -- No constraints for unlifted types
- -- Where they are legal we generate specilised function calls
-
- -- See Note [Superclasses of derived instance]
- sc_constraints = substTheta (zipOpenTvSubst (classTyVars cls) inst_tys)
- (classSCTheta cls)
- inst_tys = [mkTyConApp tycon tc_args]
-
- stupid_subst = zipTopTvSubst (tyConTyVars rep_tc) rep_tc_args
- stupid_constraints = substTheta stupid_subst (tyConStupidTheta rep_tc)
- all_constraints = stupid_constraints ++ sc_constraints ++ ordinary_constraints
-
+ ; let inst_tys = [mkTyConApp tycon tc_args]
+ inferred_constraints = inferConstraints tvs cls inst_tys rep_tc rep_tc_args
spec = DS { ds_loc = loc, ds_orig = orig
, ds_name = dfun_name, ds_tvs = tvs
- , ds_cls = cls, ds_tys = inst_tys, ds_tc = rep_tc
- , ds_theta = mtheta `orElse` all_constraints
+ , ds_cls = cls, ds_tys = inst_tys
+ , ds_tc = rep_tc, ds_tc_args = rep_tc_args
+ , ds_theta = mtheta `orElse` inferred_constraints
, ds_newtype = False }
; return (if isJust mtheta then Right spec -- Specified context
else Left spec) } -- Infer context
-mk_typeable_eqn orig tvs cls tycon tc_args rep_tc _rep_tc_args mtheta
+mk_typeable_eqn orig tvs cls tycon tc_args rep_tc rep_tc_args mtheta
-- The Typeable class is special in several ways
-- data T a b = ... deriving( Typeable )
-- gives
; loc <- getSrcSpanM
; return (Right $
DS { ds_loc = loc, ds_orig = orig, ds_name = dfun_name, ds_tvs = []
- , ds_cls = cls, ds_tys = [mkTyConApp tycon []], ds_tc = rep_tc
+ , ds_cls = cls, ds_tys = [mkTyConApp tycon []]
+ , ds_tc = rep_tc, ds_tc_args = rep_tc_args
, ds_theta = mtheta `orElse` [], ds_newtype = False }) }
+
+inferConstraints :: [TyVar] -> Class -> [TcType] -> TyCon -> [TcType] -> ThetaType
+-- Generate a sufficiently large set of constraints that typechecking the
+-- generated method definitions should succeed. This set will be simplified
+-- before being used in the instance declaration
+inferConstraints tvs cls inst_tys rep_tc rep_tc_args
+ = ASSERT2( equalLength rep_tc_tvs all_rep_tc_args, ppr cls <+> ppr rep_tc )
+ stupid_constraints ++ extra_constraints
+ ++ sc_constraints ++ con_arg_constraints
+ where
+ -- Constraints arising from the arguments of each constructor
+ con_arg_constraints
+ = [ mkClassPred cls [arg_ty]
+ | data_con <- tyConDataCons rep_tc,
+ arg_ty <- ASSERT( isVanillaDataCon data_con )
+ get_constrained_tys $
+ dataConInstOrigArgTys data_con all_rep_tc_args,
+ not (isUnLiftedType arg_ty) ]
+ -- No constraints for unlifted types
+ -- Where they are legal we generate specilised function calls
+
+ -- For functor-like classes, two things are different
+ -- (a) We recurse over argument types to generate constraints
+ -- See Functor examples in TcGenDeriv
+ -- (b) The rep_tc_args will be one short
+ is_functor_like = getUnique cls `elem` functorLikeClassKeys
+
+ get_constrained_tys :: [Type] -> [Type]
+ get_constrained_tys tys
+ | is_functor_like = concatMap (deepSubtypesContaining last_tv) tys
+ | otherwise = tys
+
+ rep_tc_tvs = tyConTyVars rep_tc
+ last_tv = last rep_tc_tvs
+ all_rep_tc_args | is_functor_like = rep_tc_args ++ [mkTyVarTy last_tv]
+ | otherwise = rep_tc_args
+
+ -- Constraints arising from superclasses
+ -- See Note [Superclasses of derived instance]
+ sc_constraints = substTheta (zipOpenTvSubst (classTyVars cls) inst_tys)
+ (classSCTheta cls)
+
+ -- Stupid constraints
+ stupid_constraints = substTheta subst (tyConStupidTheta rep_tc)
+ subst = zipTopTvSubst rep_tc_tvs all_rep_tc_args
+
+ -- Extra constraints
+ -- The Data class (only) requires that for
+ -- instance (...) => Data (T a b)
+ -- then (Data a, Data b) are among the (...) constraints
+ -- Reason: that's what you need to typecheck the method
+ -- dataCast1 f = gcast1 f
+ extra_constraints
+ | cls `hasKey` dataClassKey = [mkClassPred cls [mkTyVarTy tv] | tv <- tvs]
+ | otherwise = []
+
------------------------------------------------------------------
-- Check side conditions that dis-allow derivability for particular classes
-- This is *apart* from the newtype-deriving mechanism
| DerivableClassError SDoc -- Standard class, but can't do it
| NonDerivableClass -- Non-standard class
-checkSideConditions :: Bool -> Class -> [TcType] -> TyCon -> DerivStatus
-checkSideConditions mayDeriveDataTypeable cls cls_tys rep_tc
+checkSideConditions :: DynFlags -> Class -> [TcType] -> TyCon -> DerivStatus
+checkSideConditions dflags cls cls_tys rep_tc
| Just cond <- sideConditions cls
- = case (cond (mayDeriveDataTypeable, rep_tc)) of
+ = case (cond (dflags, rep_tc)) of
Just err -> DerivableClassError err -- Class-specific error
Nothing | null cls_tys -> CanDerive
| otherwise -> DerivableClassError ty_args_why -- e.g. deriving( Eq s )
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)
+ | 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)
+ | cls_key == functorClassKey = Just (cond_functorOK True) -- NB: no cond_std!
+ | cls_key == foldableClassKey = Just (cond_functorOK False) -- Functor/Fold/Trav works ok for rank-n types
+ | cls_key == traversableClassKey = Just (cond_functorOK False)
| getName cls `elem` typeableClassNames = Just (cond_mayDeriveDataTypeable `andCond` cond_typeableOK)
| otherwise = Nothing
where
cls_key = getUnique cls
-type Condition = (Bool, TyCon) -> Maybe SDoc
- -- Bool is whether or not we are allowed to derive Data and Typeable
+type Condition = (DynFlags, TyCon) -> Maybe SDoc
+ -- first Bool is whether or not we are allowed to derive Data and Typeable
+ -- second Bool is whether or not we are allowed to derive Functor
-- TyCon is the *representation* tycon if the
-- data type is an indexed one
-- Nothing => OK
cond_std :: Condition
cond_std (_, rep_tc)
- | any (not . isVanillaDataCon) data_cons = Just existential_why
- | null data_cons = Just no_cons_why
- | otherwise = Nothing
+ | null data_cons = Just no_cons_why
+ | not (null con_whys) = Just (vcat con_whys)
+ | otherwise = Nothing
where
data_cons = tyConDataCons rep_tc
no_cons_why = quotes (pprSourceTyCon rep_tc) <+>
ptext (sLit "has no data constructors")
- existential_why = quotes (pprSourceTyCon rep_tc) <+>
- ptext (sLit "has non-Haskell-98 constructor(s)")
+
+ con_whys = mapCatMaybes check_con data_cons
+
+ check_con :: DataCon -> Maybe SDoc
+ check_con con
+ | isVanillaDataCon con
+ , all isTauTy (dataConOrigArgTys con) = Nothing
+ | otherwise = Just (badCon con (ptext (sLit "does not have a Haskell-98 type")))
cond_enumOrProduct :: Condition
cond_enumOrProduct = cond_isEnumeration `orCond`
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)
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
+-- Currently: (a) at least one argument
+-- (b) don't use argument contravariantly
+-- (c) don't use argument in the wrong place, e.g. data T a = T (X a a)
+-- (d) optionally: don't use function types
+cond_functorOK allowFunctions (dflags, rep_tc)
+ | not (dopt Opt_DeriveFunctor dflags)
+ = Just (ptext (sLit "You need -XDeriveFunctor to derive an instance for this class"))
+ | otherwise
+ = msum (map check_con data_cons) -- msum picks the first 'Just', if any
+ where
+ 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")
+
cond_mayDeriveDataTypeable :: Condition
-cond_mayDeriveDataTypeable (mayDeriveDataTypeable, _)
- | mayDeriveDataTypeable = Nothing
+cond_mayDeriveDataTypeable (dflags, _)
+ | dopt Opt_DeriveDataTypeable dflags = Nothing
| otherwise = Just why
where
why = ptext (sLit "You need -XDeriveDataTypeable to derive an instance for this class")
std_class_via_iso :: Class -> Bool
std_class_via_iso clas -- These standard classes can be derived for a newtype
-- using the isomorphism trick *even if no -fglasgow-exts*
- = classKey clas `elem` [eqClassKey, ordClassKey, ixClassKey, boundedClassKey]
+ = classKey clas `elem` [eqClassKey, ordClassKey, ixClassKey, boundedClassKey]
-- Not Read/Show because they respect the type
-- Not Enum, because newtypes are never in Enum
; 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 :: InstOrigin -> DynFlags -> [Var] -> Class
-> [Type] -> TyCon -> [Type] -> TyCon -> [Type]
-> Maybe ThetaType
-> TcRn EarlyDerivSpec
-mkNewTypeEqn orig mayDeriveDataTypeable newtype_deriving tvs
+mkNewTypeEqn orig dflags tvs
cls cls_tys tycon tc_args rep_tycon rep_tc_args mtheta
-- Want: instance (...) => cls (cls_tys ++ [tycon tc_args]) where ...
| can_derive_via_isomorphism && (newtype_deriving || std_class_via_iso cls)
; 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
| newtype_deriving -> bale_out cant_derive_err -- Too hard, even with newtype deriving
| otherwise -> bale_out non_std_err -- Try newtype deriving!
where
- check_conditions = checkSideConditions mayDeriveDataTypeable cls cls_tys rep_tycon
+ newtype_deriving = dopt Opt_GeneralizedNewtypeDeriving dflags
+ check_conditions = checkSideConditions dflags cls cls_tys rep_tycon
bale_out msg = failWithTc (derivingThingErr cls cls_tys inst_ty msg)
non_std_err = nonStdErr cls $$
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
-------------------------------------------------------------------
-- Figuring out whether we can only do this newtype-deriving thing
- right_arity = length cls_tys + 1 == classArity cls
+ can_derive_via_isomorphism
+ = not (non_iso_class cls)
+ && arity_ok
+ && eta_ok
+ && ats_ok
+-- && not (isRecursiveTyCon tycon) -- Note [Recursive newtypes]
- -- Never derive Read,Show,Typeable,Data this way
+ -- Never derive Read,Show,Typeable,Data by isomorphism
non_iso_class cls = className cls `elem` ([readClassName, showClassName, dataClassName] ++
typeableClassNames)
- can_derive_via_isomorphism
- = not (non_iso_class cls)
- && right_arity -- Well kinded;
- -- eg not: newtype T ... deriving( ST )
- -- because ST needs *2* type params
- && eta_ok -- Eta reduction works
- && not (isRecursiveTyCon tycon) -- Does not work for recursive tycons:
- -- newtype A = MkA [A]
- -- Don't want
- -- instance Eq [A] => Eq A !!
- -- Here's a recursive newtype that's actually OK
- -- newtype S1 = S1 [T1 ()]
- -- newtype T1 a = T1 (StateT S1 IO a ) deriving( Monad )
- -- It's currently rejected. Oh well.
- -- In fact we generate an instance decl that has method of form
- -- meth @ instTy = meth @ repTy
- -- (no coerce's). We'd need a coerce if we wanted to handle
- -- recursive newtypes too
+
+ arity_ok = length cls_tys + 1 == classArity cls
+ -- Well kinded; eg not: newtype T ... deriving( ST )
+ -- because ST needs *2* type params
-- Check that eta reduction is OK
eta_ok = nt_eta_arity <= length rep_tc_args
-- And the [a] must not mention 'b'. That's all handled
-- by nt_eta_rity.
- cant_derive_err = vcat [ptext (sLit "even with cunning newtype deriving:"),
- if isRecursiveTyCon tycon then
- ptext (sLit "the newtype may be recursive")
- else empty,
- if not right_arity then
- quotes (ppr (mkClassPred cls cls_tys)) <+> ptext (sLit "does not have arity 1")
- else empty,
- if not eta_ok then
- ptext (sLit "cannot eta-reduce the representation type enough")
- else empty
- ]
+ ats_ok = null (classATs cls)
+ -- No associated types for the class, because we don't
+ -- currently generate type 'instance' decls; and cannot do
+ -- so for 'data' instance decls
+
+ cant_derive_err
+ = vcat [ ptext (sLit "even with cunning newtype deriving:")
+ , if arity_ok then empty else arity_msg
+ , if eta_ok then empty else eta_msg
+ , if ats_ok then empty else ats_msg ]
+ arity_msg = quotes (ppr (mkClassPred cls cls_tys)) <+> ptext (sLit "does not have arity 1")
+ eta_msg = ptext (sLit "cannot eta-reduce the representation type enough")
+ ats_msg = ptext (sLit "the class has associated types")
\end{code}
+Note [Recursive newtypes]
+~~~~~~~~~~~~~~~~~~~~~~~~~
+Newtype deriving works fine, even if the newtype is recursive.
+e.g. newtype S1 = S1 [T1 ()]
+ newtype T1 a = T1 (StateT S1 IO a ) deriving( Monad )
+Remember, too, that type families are curretly (conservatively) given
+a recursive flag, so this also allows newtype deriving to work
+for type famillies.
+
+We used to exclude recursive types, because we had a rather simple
+minded way of generating the instance decl:
+ newtype A = MkA [A]
+ instance Eq [A] => Eq A -- Makes typechecker loop!
+But now we require a simple context, so it's ok.
+
%************************************************************************
%* *
| 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 $
; 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
genInst :: OverlapFlag -> DerivSpec -> TcM (InstInfo RdrName, DerivAuxBinds)
genInst oflag spec
| ds_newtype spec
- = return (InstInfo { iSpec = mkInstance1 oflag spec
- , iBinds = NewTypeDerived }, [])
+ = return (InstInfo { iSpec = mkInstance oflag (ds_theta spec) spec
+ , iBinds = NewTypeDerived co }, [])
| otherwise
= do { let loc = getSrcSpan (ds_name spec)
- inst = mkInstance1 oflag spec
+ inst = mkInstance oflag (ds_theta spec) spec
clas = ds_cls spec
- rep_tycon = ds_tc spec
-- In case of a family instance, we need to use the representation
-- tycon (after all, it has the data constructors)
iBinds = VanillaInst meth_binds [] },
aux_binds)
}
+ where
+ rep_tycon = ds_tc spec
+ rep_tc_args = ds_tc_args spec
+ co1 = case tyConFamilyCoercion_maybe rep_tycon of
+ Nothing -> IdCo
+ Just co_con -> ACo (mkTyConApp co_con rep_tc_args)
+ co2 = case newTyConCo_maybe rep_tycon of
+ Nothing -> IdCo -- The newtype is transparent; no need for a cast
+ Just co_con -> ACo (mkTyConApp co_con rep_tc_args)
+ co = co1 `mkTransCoI` co2
+
+-- Example: newtype instance N [a] = N1 (Tree a)
+-- deriving instance Eq b => Eq (N [(b,b)])
+-- From the instance, we get an implicit newtype R1:N a = N1 (Tree a)
+-- When dealing with the deriving clause
+-- co1 : N [(b,b)] ~ R1:N (b,b)
+-- co2 : R1:N (b,b) ~ Tree (b,b)
genDerivBinds :: SrcSpan -> FixityEnv -> Class -> TyCon -> (LHsBinds RdrName, DerivAuxBinds)
genDerivBinds loc fix_env clas tycon
,(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}
derivInstCtxt :: Class -> [Type] -> Message
derivInstCtxt clas inst_tys
- = vcat [ptext (sLit "Alternative fix: use a standalone 'deriving instance' declaration"),
- nest 2 (ptext (sLit "instead, so you can specify the instance context yourself")),
- ptext (sLit "When deriving the instance for") <+> parens (pprClassPred clas inst_tys)]
+ = ptext (sLit "When deriving the instance for") <+> parens (pprClassPred clas inst_tys)
badDerivedPred :: PredType -> Message
badDerivedPred pred