import ListSetOps
import Outputable
import Bag
+
+import Monad (unless)
\end{code}
%************************************************************************
%************************************************************************
\begin{code}
-tcDeriving :: [LTyClDecl Name] -- All type constructors
+tcDeriving :: [LTyClDecl Name] -- All type constructors
+ -> [LInstDecl Name] -- All instance declarations
-> [LDerivDecl Name] -- All stand-alone deriving declarations
-> TcM ([InstInfo], -- The generated "instance decls"
HsValBinds Name) -- Extra generated top-level bindings
-tcDeriving tycl_decls deriv_decls
+tcDeriving tycl_decls inst_decls deriv_decls
= recoverM (returnM ([], emptyValBindsOut)) $
do { -- Fish the "deriving"-related information out of the TcEnv
-- and make the necessary "equations".
- ; (ordinary_eqns, newtype_inst_info) <- makeDerivEqns tycl_decls deriv_decls
+ ; (ordinary_eqns, newtype_inst_info)
+ <- makeDerivEqns tycl_decls inst_decls deriv_decls
; (ordinary_inst_info, deriv_binds)
<- extendLocalInstEnv (map iSpec newtype_inst_info) $
\begin{code}
makeDerivEqns :: [LTyClDecl Name]
+ -> [LInstDecl Name]
-> [LDerivDecl Name]
-> TcM ([DerivEqn], -- Ordinary derivings
[InstInfo]) -- Special newtype derivings
-makeDerivEqns tycl_decls deriv_decls
+makeDerivEqns tycl_decls inst_decls deriv_decls
= do { eqns1 <- mapM deriveTyData $
- [ (p,d) | d@(L _ (TyData {tcdDerivs = Just preds})) <- tycl_decls
- , p <- preds ]
+ extractTyDataPreds tycl_decls ++
+ [ pd -- traverse assoc data families
+ | L _ (InstDecl _ _ _ ats) <- inst_decls
+ , pd <- extractTyDataPreds ats ]
; eqns2 <- mapM deriveStandalone deriv_decls
; return ([eqn | (Just eqn, _) <- eqns1 ++ eqns2],
[inst | (_, Just inst) <- eqns1 ++ eqns2]) }
+ where
+ extractTyDataPreds decls =
+ [(p, d) | d@(L _ (TyData {tcdDerivs = Just preds})) <- decls, p <- preds]
+
------------------------------------------------------------------
deriveStandalone :: LDerivDecl Name -> TcM (Maybe DerivEqn, Maybe InstInfo)
-- 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 } }
+deriveTyData (deriv_pred, other_decl)
+ = panic "derivTyData" -- Caller ensures that only TyData can happen
------------------------------------------------------------------
mkEqnHelp orig tvs cls cls_tys tc_app
full_tc_args = tc_args ++ mkTyVarTys extra_tvs
full_tvs = tvs ++ extra_tvs
- ; (rep_tc, rep_tc_args) <- tcLookupFamInst tycon full_tc_args
+ ; (rep_tc, rep_tc_args) <- tcLookupFamInstExact tycon full_tc_args
; gla_exts <- doptM Opt_GlasgowExts
; overlap_flag <- getOverlapFlag
- ; if isDataTyCon tycon then
+
+ -- Be careful to test rep_tc here: in the case of families, we want
+ -- to check the instance tycon, not the family tycon
+ ; if isDataTyCon rep_tc then
mkDataTypeEqn orig gla_exts full_tvs cls cls_tys
tycon full_tc_args rep_tc rep_tc_args
else
baleOut err = addErrTc err >> returnM (Nothing, Nothing)
\end{code}
+Auxiliary lookup wrapper which requires that looked up family instances are
+not type instances.
+
+\begin{code}
+tcLookupFamInstExact :: TyCon -> [Type] -> TcM (TyCon, [Type])
+tcLookupFamInstExact tycon tys
+ = do { result@(rep_tycon, rep_tys) <- tcLookupFamInst tycon tys
+ ; let { tvs = map (Type.getTyVar
+ "TcDeriv.tcLookupFamInstExact")
+ rep_tys
+ ; variable_only_subst = all Type.isTyVarTy rep_tys &&
+ sizeVarSet (mkVarSet tvs) == length tvs
+ -- renaming may have no repetitions
+ }
+ ; unless variable_only_subst $
+ famInstNotFound tycon tys [result]
+ ; return result
+ }
+
+\end{code}
+
%************************************************************************
%* *
; let ordinary_constraints
= [ mkClassPred cls [arg_ty]
| data_con <- tyConDataCons rep_tc,
- arg_ty <- dataConInstOrigArgTys data_con rep_tc_args,
+ arg_ty <- ASSERT( isVanillaDataCon data_con )
+ dataConInstOrigArgTys data_con rep_tc_args,
not (isUnLiftedType arg_ty) ] -- No constraints for unlifted types?
tiresome_subst = zipTopTvSubst (tyConTyVars rep_tc) rep_tc_args
| isProductTyCon rep_tc = Nothing
| otherwise = Just why
where
- why = (pprSourceTyCon rep_tc) <+>
+ why = quotes (pprSourceTyCon rep_tc) <+>
ptext SLIT("has more than one constructor")
cond_typeableOK :: Condition
where
why = ptext SLIT("You need -fglasgow-exts to derive an instance for this class")
-std_class gla_exts clas
- = key `elem` derivableClassKeys
- || (gla_exts && (key == typeableClassKey || key == dataClassKey))
- where
- key = classKey clas
-
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]
new_dfun_name clas tycon -- Just a simple wrapper
- = newDFunName clas [mkTyConApp tycon []] (getSrcLoc tycon)
+ = newDFunName clas [mkTyConApp tycon []] (getSrcSpan tycon)
-- The type passed to newDFunName is only used to generate
-- a suitable string; hence the empty type arg list
\end{code}
tycon tc_args
rep_tycon rep_tc_args
| can_derive_via_isomorphism && (gla_exts || std_class_via_iso cls)
- = do { traceTc (text "newtype deriving:" <+> ppr tycon <+> ppr rep_tys)
- ; -- Go ahead and use the isomorphism
- dfun_name <- new_dfun_name cls tycon
- ; return (Nothing, Just (InstInfo { iSpec = mk_inst_spec dfun_name,
- iBinds = NewTypeDerived ntd_info })) }
- | std_class gla_exts cls
- = mkDataTypeEqn orig gla_exts tvs cls cls_tys tycon tc_args rep_tycon rep_tc_args -- Go via bale-out route
-
- -- Otherwise its a non-standard instance
+ = do { traceTc (text "newtype deriving:" <+> ppr tycon <+> ppr rep_tys)
+ ; -- Go ahead and use the isomorphism
+ dfun_name <- new_dfun_name cls tycon
+ ; return (Nothing, Just (InstInfo { iSpec = mk_inst_spec dfun_name,
+ iBinds = NewTypeDerived ntd_info })) }
+
+ | isNothing mb_std_err -- Use the standard H98 method
+ = do { loc <- getSrcSpanM
+ ; eqn <- mk_data_eqn loc orig tvs cls tycon tc_args rep_tycon rep_tc_args
+ ; return (Just eqn, Nothing) }
+
+ -- Otherwise we can't derive
| gla_exts = baleOut cant_derive_err -- Too hard
- | otherwise = baleOut non_std_err -- Just complain about being a non-std instance
+ | otherwise = baleOut std_err -- Just complain about being a non-std instance
where
+ mb_std_err = checkSideConditions gla_exts cls cls_tys rep_tycon
+ std_err = derivingThingErr cls cls_tys tc_app $
+ vcat [fromJust mb_std_err,
+ ptext SLIT("Try -fglasgow-exts 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, ...)
-- where t is a type,
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 is recursive")
+ 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")
ptext SLIT("the eta-reduction property does not hold")
else empty
])
-
- non_std_err = derivingThingErr cls cls_tys tc_app
- (vcat [non_std_why cls,
- ptext SLIT("Try -fglasgow-exts for GHC's newtype-deriving extension")])
\end{code}
gen_soln :: DerivEqn -> TcM [PredType]
gen_soln (loc, orig, _, tyvars, clas, inst_ty, deriv_rhs)
= setSrcSpan loc $
+ addErrCtxt (derivInstCtxt clas [inst_ty]) $
do { theta <- tcSimplifyDeriv orig tyvars deriv_rhs
- ; addErrCtxt (derivInstCtxt theta clas [inst_ty]) $
- do { checkNoErrs (checkValidInstance tyvars theta clas [inst_ty])
- -- See Note [Deriving context]
- -- If this fails, don't continue
+ -- checkValidInstance tyvars theta clas [inst_ty]
+ -- Not necessary; see Note [Exotic derived instance contexts]
+ -- in TcSimplify
-- Check for a bizarre corner case, when the derived instance decl should
-- have form instance C a b => D (T a) where ...
-- 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
+ ; return (sortLe (<=) theta) } -- Canonicalise before returning the solution
------------------------------------------------------------------
mk_inst_spec :: DerivEqn -> DerivSoln -> Instance
; setGblEnv env' thing_inside }
\end{code}
-Note [Deriving context]
-~~~~~~~~~~~~~~~~~~~~~~~
-With -fglasgow-exts, we allow things like (C Int a) in the simplified
-context for a derived instance declaration, because at a use of this
-instance, we might know that a=Bool, and have an instance for (C Int
-Bool)
-
-We nevertheless insist that each predicate meets the termination
-conditions. If not, the deriving mechanism generates larger and larger
-constraints. Example:
- data Succ a = S a
- data Seq a = Cons a (Seq (Succ a)) | Nil deriving Show
-
-Note the lack of a Show instance for Succ. First we'll generate
- instance (Show (Succ a), Show a) => Show (Seq a)
-and then
- instance (Show (Succ (Succ a)), Show (Succ a), Show a) => Show (Seq a)
-and so on. Instead we want to complain of no instance for (Show (Succ a)).
-
%************************************************************************
%* *
-- In case of a family instance, we need to use the representation
-- tycon (after all, it has the data constructors)
- ; (tycon, _) <- tcLookupFamInst visible_tycon tyArgs
+ ; (tycon, _) <- tcLookupFamInstExact visible_tycon tyArgs
; let (meth_binds, aux_binds) = genDerivBinds clas fix_env tycon
-- Bring the right type variables into
standaloneCtxt :: LHsType Name -> SDoc
standaloneCtxt ty = ptext SLIT("In the stand-alone deriving instance for") <+> quotes (ppr ty)
-derivInstCtxt theta clas inst_tys
- = hang (ptext SLIT("In the derived instance:"))
- 2 (pprThetaArrow theta <+> pprClassPred clas inst_tys)
--- Used for the ...Thetas variants; all top level
+derivInstCtxt clas inst_tys
+ = ptext SLIT("When deriving the instance for") <+> parens (pprClassPred clas inst_tys)
badDerivedPred pred
= vcat [ptext SLIT("Can't derive instances where the instance context mentions"),
nest 2 (ptext SLIT("Offending constraint:") <+> ppr pred)]
\end{code}
+