| 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 )
- get_constrained_tys $
- substTys subst $
- 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
-
-
- -- See Note [Superclasses of derived instance]
- sc_constraints = substTheta (zipOpenTvSubst (classTyVars cls) inst_tys)
- (classSCTheta cls)
- inst_tys = [mkTyConApp tycon tc_args]
- subst = zipTopTvSubst rep_tc_tvs all_rep_tc_args
- stupid_constraints = substTheta 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_tc_args = rep_tc_args
- , ds_theta = mtheta `orElse` all_constraints
+ , ds_theta = mtheta `orElse` inferred_constraints
, ds_newtype = False }
- ; ASSERT2( equalLength rep_tc_tvs all_rep_tc_args, ppr cls <+> ppr tycon )
- return (if isJust mtheta then Right spec -- Specified 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
, 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
dataTypeOf _ = $dT
+ dataCast1 = gcast1 -- If T :: * -> *
+ dataCast2 = gcast2 -- if T :: * -> * -> *
+
+
\begin{code}
gen_Data_binds :: SrcSpan
-> TyCon
-> (LHsBinds RdrName, -- The method bindings
DerivAuxBinds) -- Auxiliary bindings
gen_Data_binds loc tycon
- = (listToBag [gfoldl_bind, gunfold_bind, toCon_bind, dataTypeOf_bind],
+ = (listToBag [gfoldl_bind, gunfold_bind, toCon_bind, dataTypeOf_bind]
+ `unionBags` gcast_binds,
-- Auxiliary definitions: the data type and constructors
MkTyCon tycon : map MkDataCon data_cons)
where
[nlWildPat]
(nlHsVar (mk_data_type_name tycon))
+ ------------ gcast1/2
+ tycon_kind = tyConKind tycon
+ gcast_binds | tycon_kind `eqKind` kind1 = mk_gcast dataCast1_RDR gcast1_RDR
+ | tycon_kind `eqKind` kind2 = mk_gcast dataCast2_RDR gcast2_RDR
+ | otherwise = emptyBag
+ mk_gcast dataCast_RDR gcast_RDR
+ = unitBag (mk_easy_FunBind loc dataCast_RDR [nlVarPat f_RDR]
+ (nlHsVar gcast_RDR `nlHsApp` nlHsVar f_RDR))
+
+
+kind1, kind2 :: Kind
+kind1 = liftedTypeKind `mkArrowKind` liftedTypeKind
+kind2 = liftedTypeKind `mkArrowKind` kind1
gfoldl_RDR, gunfold_RDR, toConstr_RDR, dataTypeOf_RDR, mkConstr_RDR,
- mkDataType_RDR, conIndex_RDR, prefix_RDR, infix_RDR :: RdrName
+ mkDataType_RDR, conIndex_RDR, prefix_RDR, infix_RDR,
+ dataCast1_RDR, dataCast2_RDR, gcast1_RDR, gcast2_RDR :: RdrName
gfoldl_RDR = varQual_RDR gENERICS (fsLit "gfoldl")
gunfold_RDR = varQual_RDR gENERICS (fsLit "gunfold")
toConstr_RDR = varQual_RDR gENERICS (fsLit "toConstr")
dataTypeOf_RDR = varQual_RDR gENERICS (fsLit "dataTypeOf")
+dataCast1_RDR = varQual_RDR gENERICS (fsLit "dataCast1")
+dataCast2_RDR = varQual_RDR gENERICS (fsLit "dataCast2")
+gcast1_RDR = varQual_RDR tYPEABLE (fsLit "gcast1")
+gcast2_RDR = varQual_RDR tYPEABLE (fsLit "gcast2")
mkConstr_RDR = varQual_RDR gENERICS (fsLit "mkConstr")
mkDataType_RDR = varQual_RDR gENERICS (fsLit "mkDataType")
conIndex_RDR = varQual_RDR gENERICS (fsLit "constrIndex")