X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Ftypecheck%2FTcDeriv.lhs;h=6934eb1d2f463259d45d209f86388b95c2b5f554;hb=ab241c5d6187a93acffc609bdbffdae30ff9b284;hp=af537409cfe876c2a35618a55ad1203e479ebade;hpb=3548802de235eca280982270463db84910ee3748;p=ghc-hetmet.git diff --git a/compiler/typecheck/TcDeriv.lhs b/compiler/typecheck/TcDeriv.lhs index af53740..6934eb1 100644 --- a/compiler/typecheck/TcDeriv.lhs +++ b/compiler/typecheck/TcDeriv.lhs @@ -47,6 +47,8 @@ import Util import ListSetOps import Outputable import Bag + +import Monad (unless) \end{code} %************************************************************************ @@ -381,6 +383,8 @@ deriveTyData (deriv_pred, L loc decl@(TyData { tcdLName = L _ tycon_name, -- 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 @@ -393,11 +397,14 @@ 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 @@ -410,6 +417,27 @@ mkEqnHelp orig tvs cls cls_tys tc_app 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} + %************************************************************************ %* * @@ -420,6 +448,7 @@ baleOut err = addErrTc err >> returnM (Nothing, Nothing) \begin{code} mkDataTypeEqn orig gla_exts tvs cls cls_tys tycon tc_args rep_tc rep_tc_args | Just err <- checkSideConditions gla_exts cls cls_tys rep_tc + -- NB: pass the *representation* tycon to checkSideConditions = baleOut (derivingThingErr cls cls_tys (mkTyConApp tycon tc_args) err) | otherwise @@ -496,7 +525,11 @@ sideConditions (dataClassKey, cond_glaExts `andCond` cond_std) ] -type Condition = (Bool, TyCon) -> Maybe SDoc -- Nothing => OK +type Condition = (Bool, TyCon) -> Maybe SDoc + -- Bool is gla-exts flag + -- TyCon is the *representation* tycon if the + -- data type is an indexed one + -- Nothing => OK orCond :: Condition -> Condition -> Condition orCond c1 c2 tc @@ -536,7 +569,7 @@ cond_isProduct (gla_exts, rep_tc) | 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 @@ -563,21 +596,15 @@ cond_glaExts (gla_exts, _rep_tc) | gla_exts = Nothing 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] -- Not Read/Show because they respect the type - -- Not Enum, becuase newtypes are never in Enum + -- Not Enum, because newtypes are never in Enum 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} @@ -594,18 +621,26 @@ mkNewTypeEqn orig gla_exts overlap_flag tvs cls cls_tys 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, @@ -747,7 +782,7 @@ mkNewTypeEqn orig gla_exts overlap_flag tvs cls cls_tys 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") @@ -760,10 +795,6 @@ mkNewTypeEqn orig gla_exts overlap_flag tvs cls cls_tys 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} @@ -872,6 +903,26 @@ extendLocalInstEnv dfuns thing_inside ; 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)). + + %************************************************************************ %* * \subsection[TcDeriv-normal-binds]{Bindings for the various classes} @@ -952,7 +1003,7 @@ genInst spec -- 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 @@ -1097,3 +1148,4 @@ badDerivedPred pred nest 2 (ptext SLIT("Offending constraint:") <+> ppr pred)] \end{code} +