import Generics
import TcRnMonad
import TcEnv
-import TcGenDeriv -- Deriv stuff
+import TcClassDcl( tcAddDeclCtxt ) -- Small helper
+import TcGenDeriv -- Deriv stuff
import InstEnv
import Inst
import TcHsType
+import TcMType
import TcSimplify
import RnBinds
So, here are the synonyms for the ``equation'' structures:
\begin{code}
-type DerivEqn = (SrcSpan, InstOrigin, Name, Class, TyCon, [TyVar], DerivRhs)
- -- The Name is the name for the DFun we'll build
- -- The tyvars bind all the variables in the RHS
- -- For family indexes, the tycon is the representation tycon
-
-pprDerivEqn :: DerivEqn -> SDoc
-pprDerivEqn (l, _, n, c, tc, tvs, rhs)
- = parens (hsep [ppr l, ppr n, ppr c, ppr origTc, ppr tys] <+> equals <+>
- ppr rhs)
- where
- (origTc, tys) = tyConOrigHead tc
-
type DerivRhs = ThetaType
type DerivSoln = DerivRhs
+type DerivEqn = (SrcSpan, InstOrigin, Name, [TyVar], Class, Type, DerivRhs)
+ -- (span, orig, df, tvs, C, ty, rhs)
+ -- implies a dfun declaration of the form
+ -- df :: forall tvs. rhs => C ty
+ -- The Name is the name for the DFun we'll build
+ -- The tyvars bind all the variables in the RHS
+ -- For family indexes, the tycon is the *family* tycon
+ -- (not the representation tycon)
+
+pprDerivEqn :: DerivEqn -> SDoc
+pprDerivEqn (l, _, n, tvs, c, ty, rhs)
+ = parens (hsep [ppr l, ppr n, ppr tvs, ppr c, ppr ty]
+ <+> equals <+> ppr rhs)
\end{code}
= recoverM (returnM ([], emptyValBindsOut)) $
do { -- Fish the "deriving"-related information out of the TcEnv
-- and make the necessary "equations".
- overlap_flag <- getOverlapFlag
- ; (ordinary_eqns, newtype_inst_info)
- <- makeDerivEqns overlap_flag tycl_decls deriv_decls
+ ; (ordinary_eqns, newtype_inst_info) <- makeDerivEqns tycl_decls deriv_decls
; (ordinary_inst_info, deriv_binds)
<- extendLocalInstEnv (map iSpec newtype_inst_info) $
- deriveOrdinaryStuff overlap_flag ordinary_eqns
+ deriveOrdinaryStuff ordinary_eqns
-- Add the newtype-derived instances to the inst env
-- before tacking the "ordinary" ones
= vcat (map pprInstInfoDetails inst_infos) $$ ppr extra_binds
-----------------------------------------
-deriveOrdinaryStuff overlap_flag [] -- Short cut
+deriveOrdinaryStuff [] -- Short cut
= returnM ([], emptyLHsBinds)
-deriveOrdinaryStuff overlap_flag eqns
+deriveOrdinaryStuff eqns
= do { -- Take the equation list and solve it, to deliver a list of
-- solutions, a.k.a. the contexts for the instance decls
-- required for the corresponding equations.
- inst_specs <- solveDerivEqns overlap_flag eqns
+ overlap_flag <- getOverlapFlag
+ ; inst_specs <- solveDerivEqns overlap_flag eqns
-- Generate the InstInfo for each dfun,
-- plus any auxiliary bindings it needs
\begin{code}
-type DerivSpec = (SrcSpan, -- location of the deriving clause
- InstOrigin, -- deriving at data decl or standalone?
- NewOrData, -- newtype or data type
- Name, -- Type constructor for which we derive
- [LHsTyVarBndr Name], -- Type variables
- Maybe [LHsType Name], -- Type indexes if indexed type
- LHsType Name) -- Class instance to be generated
-
-makeDerivEqns :: OverlapFlag
- -> [LTyClDecl Name]
+makeDerivEqns :: [LTyClDecl Name]
-> [LDerivDecl Name]
-> TcM ([DerivEqn], -- Ordinary derivings
[InstInfo]) -- Special newtype derivings
-makeDerivEqns overlap_flag tycl_decls deriv_decls
- = do derive_top_level <- mapM top_level_deriv deriv_decls
- (maybe_ordinaries, maybe_newtypes)
- <- mapAndUnzipM mk_eqn (derive_data ++ catMaybes derive_top_level)
- return (catMaybes maybe_ordinaries, catMaybes maybe_newtypes)
+makeDerivEqns tycl_decls deriv_decls
+ = do { eqns1 <- mapM deriveTyData $
+ [ (p,d) | d@(L _ (TyData {tcdDerivs = Just preds})) <- tycl_decls
+ , p <- preds ]
+ ; eqns2 <- mapM deriveStandalone deriv_decls
+ ; return ([eqn | (Just eqn, _) <- eqns1 ++ eqns2],
+ [inst | (_, Just inst) <- eqns1 ++ eqns2]) }
+
+------------------------------------------------------------------
+deriveStandalone :: LDerivDecl Name -> TcM (Maybe DerivEqn, Maybe InstInfo)
+-- Standalone deriving declarations
+-- e.g. derive instance Show T
+-- Rather like tcLocalInstDecl
+deriveStandalone (L loc (DerivDecl deriv_ty))
+ = setSrcSpan loc $
+ addErrCtxt (standaloneCtxt deriv_ty) $
+ do { (tvs, theta, tau) <- tcHsInstHead deriv_ty
+ ; (cls, inst_tys) <- checkValidInstHead tau
+ ; let cls_tys = take (length inst_tys - 1) inst_tys
+ inst_ty = last inst_tys
+
+ ; mkEqnHelp StandAloneDerivOrigin tvs cls cls_tys inst_ty }
+
+------------------------------------------------------------------
+deriveTyData :: (LHsType Name, LTyClDecl Name) -> TcM (Maybe DerivEqn, Maybe InstInfo)
+deriveTyData (deriv_pred, L loc decl@(TyData { tcdLName = L _ tycon_name,
+ tcdTyVars = tv_names,
+ tcdTyPats = ty_pats }))
+ = setSrcSpan loc $
+ 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
+ ; 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 } }
+
+------------------------------------------------------------------
+mkEqnHelp orig tvs cls cls_tys tc_app
+ | Just (tycon, tc_args) <- tcSplitTyConApp_maybe tc_app
+ = do { -- Make tc_app saturated, because that's what the
+ -- mkDataTypeEqn things expect
+ -- It might not be saturated in the standalone deriving case
+ -- derive instance Monad (T a)
+ let extra_tvs = dropList tc_args (tyConTyVars tycon)
+ full_tc_args = tc_args ++ mkTyVarTys extra_tvs
+ full_tvs = tvs ++ extra_tvs
+
+ ; (rep_tc, rep_tc_args) <- tcLookupFamInst tycon full_tc_args
+
+ ; gla_exts <- doptM Opt_GlasgowExts
+ ; overlap_flag <- getOverlapFlag
+ ; if isDataTyCon tycon then
+ mkDataTypeEqn orig gla_exts full_tvs cls cls_tys
+ tycon full_tc_args rep_tc rep_tc_args
+ else
+ mkNewTypeEqn orig gla_exts overlap_flag full_tvs cls cls_tys
+ tycon full_tc_args rep_tc rep_tc_args }
+ | otherwise
+ = baleOut (derivingThingErr cls cls_tys tc_app
+ (ptext SLIT("Last argument of the instance must be a type application")))
+
+baleOut err = addErrTc err >> returnM (Nothing, Nothing)
+\end{code}
+
+
+%************************************************************************
+%* *
+ Deriving data types
+%* *
+%************************************************************************
+
+\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 tycon tc_args
+ = baleOut (derivingThingErr cls cls_tys (mkTyConApp tycon tc_args) err)
+
+ | otherwise
+ = ASSERT( null cls_tys )
+ do { loc <- getSrcSpanM
+ ; eqn <- mk_data_eqn loc orig tvs cls tycon tc_args rep_tc rep_tc_args
+ ; return (Just eqn, Nothing) }
+
+mk_data_eqn :: SrcSpan -> InstOrigin -> [TyVar] -> Class
+ -> TyCon -> [TcType] -> TyCon -> [TcType] -> TcM DerivEqn
+mk_data_eqn loc orig tvs cls tycon tc_args rep_tc rep_tc_args
+ | cls `hasKey` typeableClassKey
+ = -- The Typeable class is special in several ways
+ -- data T a b = ... deriving( Typeable )
+ -- gives
+ -- instance Typeable2 T where ...
+ -- Notice that:
+ -- 1. There are no constraints in the instance
+ -- 2. There are no type variables either
+ -- 3. The actual class we want to generate isn't necessarily
+ -- Typeable; it depends on the arity of the type
+ do { real_clas <- tcLookupClass (typeableClassNames !! tyConArity tycon)
+ ; dfun_name <- new_dfun_name real_clas tycon
+ ; return (loc, orig, dfun_name, [], real_clas, mkTyConApp tycon [], []) }
+
+ | otherwise
+ = do { dfun_name <- new_dfun_name cls tycon
+ ; let ordinary_constraints
+ = [ mkClassPred cls [arg_ty]
+ | data_con <- tyConDataCons rep_tc,
+ arg_ty <- dataConInstOrigArgTys data_con rep_tc_args,
+ not (isUnLiftedType arg_ty) ] -- No constraints for unlifted types?
+
+ tiresome_subst = zipTopTvSubst (tyConTyVars rep_tc) rep_tc_args
+ stupid_constraints = substTheta tiresome_subst (tyConStupidTheta rep_tc)
+ -- see note [Data decl contexts] above
+
+ ; return (loc, orig, dfun_name, tvs, cls, mkTyConApp tycon tc_args,
+ stupid_constraints ++ ordinary_constraints)
+ }
+
+------------------------------------------------------------------
+-- Check side conditions that dis-allow derivability for particular classes
+-- This is *apart* from the newtype-deriving mechanism
+
+checkSideConditions :: Bool -> Class -> [TcType] -> TyCon -> [TcType] -> Maybe SDoc
+checkSideConditions gla_exts cls cls_tys tycon tc_tys
+ | notNull cls_tys
+ = Just ty_args_why -- e.g. deriving( Foo s )
+ | otherwise
+ = case [cond | (key,cond) <- sideConditions, key == getUnique cls] of
+ [] -> Just (non_std_why cls)
+ [cond] -> cond (gla_exts, tycon)
+ other -> pprPanic "checkSideConditions" (ppr cls)
where
- ------------------------------------------------------------------
- -- Deriving clauses at data declarations
- derive_data :: [DerivSpec]
- derive_data = [ (loc, DerivOrigin, nd, tycon, tyVars, tyPats, pred)
- | L loc (TyData { tcdND = nd, tcdLName = L _ tycon,
- tcdTyVars = tyVars, tcdTyPats = tyPats,
- tcdDerivs = Just preds }) <- tycl_decls,
- pred <- preds ]
-
- -- Standalone deriving declarations
- top_level_deriv :: LDerivDecl Name -> TcM (Maybe DerivSpec)
- top_level_deriv d@(L loc (DerivDecl inst ty_name)) =
- recoverM (returnM Nothing) $ setSrcSpan loc $
- do tycon <- tcLookupLocatedTyCon ty_name
- let new_or_data = if isNewTyCon tycon then NewType else DataType
- let tyVars = [ noLoc $ KindedTyVar (tyVarName tv) (tyVarKind tv)
- | tv <- tyConTyVars tycon] -- Yuk!!!
- traceTc (text "Stand-alone deriving:" <+>
- ppr (new_or_data, unLoc ty_name, inst))
- return $ Just (loc, StandAloneDerivOrigin, new_or_data,
- unLoc ty_name, tyVars, Nothing, inst)
+ ty_args_why = quotes (ppr (mkClassPred cls cls_tys)) <+> ptext SLIT("is not a class")
- ------------------------------------------------------------------
- -- Derive equation/inst info for one deriving clause (data or standalone)
- mk_eqn :: DerivSpec -> TcM (Maybe DerivEqn, Maybe InstInfo)
- -- We swizzle the datacons out of the tycon to make the rest of the
- -- equation. We can't get the tyvars out of the constructor in case
- -- of family instances, as we already need to them to lookup the
- -- representation tycon (only that has the right set of type
- -- variables, the type variables of the family constructor are
- -- different).
- --
- -- The "deriv_ty" is a LHsType to take account of the fact that for
- -- newtype deriving we allow deriving (forall a. C [a]).
-
- mk_eqn (loc, orig, new_or_data, tycon_name, tyvars, mb_tys, hs_deriv_ty)
- = setSrcSpan loc $
- addErrCtxt (derivCtxt tycon_name mb_tys) $
- do { named_tycon <- tcLookupTyCon tycon_name
-
- -- Enable deriving preds to mention the type variables in the
- -- instance type
- ; tcTyVarBndrs tyvars $ \tvs -> do
- { traceTc (text "TcDeriv.mk_eqn: tyvars:" <+> ppr tvs)
-
- -- Lookup representation tycon in case of a family instance
- -- NB: We already need the type variables in scope here for the
- -- call to `dsHsType'.
- ; tycon <- case mb_tys of
- Nothing -> return named_tycon
- Just hsTys -> do
- tys <- mapM dsHsType hsTys
- tcLookupFamInst named_tycon tys
-
- ; (deriv_tvs, clas, tys) <- tcHsDeriv hs_deriv_ty
- ; gla_exts <- doptM Opt_GlasgowExts
- ; mk_eqn_help loc orig gla_exts new_or_data tycon deriv_tvs clas tys
- }}
+non_std_why cls = quotes (ppr cls) <+> ptext SLIT("is not a derivable class")
- ------------------------------------------------------------------
- -- data/newtype T a = ... deriving( C t1 t2 )
- -- leads to a call to mk_eqn_help with
- -- tycon = T, deriv_tvs = ftv(t1,t2), clas = C, tys = [t1,t2]
-
- mk_eqn_help loc orig gla_exts DataType tycon deriv_tvs clas tys
- | Just err <- checkSideConditions gla_exts tycon deriv_tvs clas tys
- = bale_out (derivingThingErr clas tys origTyCon ttys err)
- | otherwise
- = do { eqn <- mkDataTypeEqn loc orig tycon clas
- ; returnM (Just eqn, Nothing) }
- where
- (origTyCon, ttys) = tyConOrigHead tycon
+sideConditions :: [(Unique, Condition)]
+sideConditions
+ = [ (eqClassKey, cond_std),
+ (ordClassKey, cond_std),
+ (readClassKey, cond_std),
+ (showClassKey, cond_std),
+ (enumClassKey, cond_std `andCond` cond_isEnumeration),
+ (ixClassKey, cond_std `andCond` (cond_isEnumeration `orCond` cond_isProduct)),
+ (boundedClassKey, cond_std `andCond` (cond_isEnumeration `orCond` cond_isProduct)),
+ (typeableClassKey, cond_glaExts `andCond` cond_typeableOK),
+ (dataClassKey, cond_glaExts `andCond` cond_std)
+ ]
+
+type Condition = (Bool, TyCon) -> Maybe SDoc -- Nothing => OK
- mk_eqn_help loc orig gla_exts NewType tycon deriv_tvs clas tys
- | can_derive_via_isomorphism && (gla_exts || std_class_via_iso clas)
- = do { traceTc (text "newtype deriving:" <+> ppr tycon <+> ppr rep_tys)
+orCond :: Condition -> Condition -> Condition
+orCond c1 c2 tc
+ = case c1 tc of
+ Nothing -> Nothing -- c1 succeeds
+ Just x -> case c2 tc of -- c1 fails
+ Nothing -> Nothing
+ Just y -> Just (x $$ ptext SLIT(" and") $$ y)
+ -- Both fail
+
+andCond c1 c2 tc = case c1 tc of
+ Nothing -> c2 tc -- c1 succeeds
+ Just x -> Just x -- c1 fails
+
+cond_std :: Condition
+cond_std (gla_exts, tycon)
+ | any (not . isVanillaDataCon) data_cons = Just existential_why
+ | null data_cons = Just no_cons_why
+ | otherwise = Nothing
+ where
+ data_cons = tyConDataCons tycon
+ no_cons_why = quotes (ppr tycon) <+> ptext SLIT("has no data constructors")
+ existential_why = quotes (ppr tycon) <+> ptext SLIT("has non-Haskell-98 constructor(s)")
+
+cond_isEnumeration :: Condition
+cond_isEnumeration (gla_exts, tycon)
+ | isEnumerationTyCon tycon = Nothing
+ | otherwise = Just why
+ where
+ why = quotes (ppr tycon) <+> ptext SLIT("has non-nullary constructors")
+
+cond_isProduct :: Condition
+cond_isProduct (gla_exts, tycon)
+ | isProductTyCon tycon = Nothing
+ | otherwise = Just why
+ where
+ why = quotes (ppr tycon) <+> ptext SLIT("has more than one constructor")
+
+cond_typeableOK :: Condition
+-- OK for Typeable class
+-- Currently: (a) args all of kind *
+-- (b) 7 or fewer args
+cond_typeableOK (gla_exts, tycon)
+ | tyConArity tycon > 7 = Just too_many
+ | not (all (isSubArgTypeKind . tyVarKind) (tyConTyVars tycon))
+ = Just bad_kind
+ | isFamInstTyCon tycon = Just fam_inst -- no Typable for family insts
+ | otherwise = Nothing
+ where
+ too_many = quotes (ppr tycon) <+> ptext SLIT("has too many arguments")
+ bad_kind = quotes (ppr tycon) <+>
+ ptext SLIT("has arguments of kind other than `*'")
+ fam_inst = quotes (ppr tycon) <+> ptext SLIT("is a type family")
+
+cond_glaExts :: Condition
+cond_glaExts (gla_exts, tycon) | gla_exts = Nothing
+ | otherwise = Just why
+ 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
+
+
+new_dfun_name clas tycon -- Just a simple wrapper
+ = newDFunName clas [mkTyConApp tycon []] (getSrcLoc tycon)
+ -- The type passed to newDFunName is only used to generate
+ -- a suitable string; hence the empty type arg list
+\end{code}
+
+
+%************************************************************************
+%* *
+ Deriving newtypes
+%* *
+%************************************************************************
+
+\begin{code}
+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 clas tycon
+ 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 clas
- = mk_eqn_help loc orig gla_exts DataType tycon deriv_tvs clas tys -- Go via bale-out route
-
- | otherwise -- Non-standard instance
- = bale_out (if gla_exts then
- cant_derive_err -- Too hard
- else
- non_std_err) -- Just complain about being a non-std instance
- where
+ | 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
+ | gla_exts = baleOut cant_derive_err -- Too hard
+ | otherwise = baleOut non_std_err -- Just complain about being a non-std instance
+ where
-- 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,
- -- ak+1...an is a suffix of a1..an
+ -- ak+1...an is a suffix of a1..an, and are all tyars
-- ak+1...an do not occur free in t, nor in the s1..sm
-- (C s1 ... sm) is a *partial applications* of class C
-- with the last parameter missing
-- We generate the instance
-- instance Monad (ST s) => Monad (T s) where
- clas_tyvars = classTyVars clas
- kind = tyVarKind (last clas_tyvars)
+ cls_tyvars = classTyVars cls
+ kind = tyVarKind (last cls_tyvars)
-- Kind of the thing we want to instance
-- e.g. argument kind of Monad, *->*
-- 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!
- (tc_tvs, rep_ty) = newTyConRhs tycon
+ rep_ty = newTyConInstRhs rep_tycon rep_tc_args
(rep_fn, rep_ty_args) = tcSplitAppTys rep_ty
- n_tyvars_to_keep = tyConArity tycon - n_args_to_drop
- tyvars_to_drop = drop n_tyvars_to_keep tc_tvs
- tyvars_to_keep = take n_tyvars_to_keep tc_tvs
+ 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
+ args_to_keep = take n_args_to_keep rep_ty_args
rep_fn' = mkAppTys rep_fn args_to_keep
- rep_tys = tys ++ [rep_fn']
- rep_pred = mkClassPred clas rep_tys
+ rep_tys = cls_tys ++ [rep_fn']
+ 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
- -- To account for newtype family instance, we need to get the family
- -- tycon and its index types when costructing the type at which we
- -- construct the class instance. The dropped class parameters must of
- -- course all be variables (not more complex indexes).
- --
- origHead = let
- (origTyCon, tyArgs) = tyConOrigHead tycon
- in mkTyConApp origTyCon (take n_tyvars_to_keep tyArgs)
+ 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
+ -- Next we figure out what superclass dictionaries to use
+ -- See Note [Newtype deriving superclasses] above
- inst_tys = tys ++ [origHead]
- sc_theta = substTheta (zipOpenTvSubst clas_tyvars inst_tys)
- (classSCTheta clas)
+ inst_tys = cls_tys ++ [tc_app]
+ sc_theta = substTheta (zipOpenTvSubst cls_tyvars inst_tys)
+ (classSCTheta cls)
-- If there are no tyvars, there's no need
-- to abstract over the dictionaries we need
-- instance C T
-- rather than
-- instance C Int => C T
- dict_tvs = deriv_tvs ++ tyvars_to_keep
+ dict_tvs = filterOut (`elemVarSet` dropped_tvs) tvs
all_preds = rep_pred : sc_theta -- NB: rep_pred comes first
(dict_args, ntd_info) | null dict_tvs = ([], Just all_preds)
| otherwise = (all_preds, Nothing)
-- Finally! Here's where we build the dictionary Id
mk_inst_spec dfun_name = mkLocalInstance dfun overlap_flag
where
- dfun = mkDictFunId dfun_name dict_tvs dict_args clas inst_tys
+ dfun = mkDictFunId dfun_name dict_tvs dict_args cls inst_tys
-------------------------------------------------------------------
-- Figuring out whether we can only do this newtype-deriving thing
- right_arity = length tys + 1 == classArity clas
+ right_arity = length cls_tys + 1 == classArity cls
-- Never derive Read,Show,Typeable,Data this way
non_iso_classes = [readClassKey, showClassKey, typeableClassKey, dataClassKey]
can_derive_via_isomorphism
- = not (getUnique clas `elem` non_iso_classes)
+ = not (getUnique cls `elem` non_iso_classes)
&& right_arity -- Well kinded;
-- eg not: newtype T ... deriving( ST )
-- because ST needs *2* type params
- && n_tyvars_to_keep >= 0 -- Type constructor has right kind:
+ && 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 )
-- recursive newtypes too
-- Check that eta reduction is OK
- -- (a) the dropped-off args are identical
- -- (b) the remaining type args do not mention any of teh dropped
- -- type variables
- -- (c) the type class args do not mention any of teh dropped type
- -- variables
- -- (d) in case of newtype family instances, the eta-dropped
- -- arguments must be type variables (not more complex indexes)
- dropped_tvs = mkVarSet tyvars_to_drop
- eta_ok = (args_to_drop `tcEqTypes` mkTyVarTys tyvars_to_drop)
+ eta_ok = (args_to_drop `tcEqTypes` dropped_tc_args)
+ -- (a) the dropped-off args are identical in the source and rep type
+ -- newtype T a b = MkT (S [a] b) deriving( Monad )
+ -- Here the 'b' must be the same in the rep type (S [a] b)
+
&& (tyVarsOfType rep_fn' `disjointVarSet` dropped_tvs)
- && (tyVarsOfTypes tys `disjointVarSet` dropped_tvs)
- && droppedIndexesAreVariables
+ -- (b) the remaining type args do not mention any of the dropped
+ -- type variables
+
+ && (tyVarsOfTypes cls_tys `disjointVarSet` dropped_tvs)
+ -- (c) the type class args do not mention any of the dropped type
+ -- variables
- droppedIndexesAreVariables =
- case tyConFamInst_maybe tycon of
- Nothing -> True
- Just (famTyCon, tyIdxs) ->
- all isTyVarTy $ drop (tyConArity famTyCon - n_args_to_drop) tyIdxs
+ && 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 clas tys tycon (mkTyVarTys tyvars_to_keep)
+ 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")
else empty,
if not right_arity then
- quotes (ppr (mkClassPred clas tys)) <+> ptext SLIT("does not have arity 1")
+ quotes (ppr (mkClassPred cls cls_tys)) <+> ptext SLIT("does not have arity 1")
else empty,
- if not (n_tyvars_to_keep >= 0) then
+ 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 empty
])
- non_std_err = derivingThingErr clas tys tycon (mkTyVarTys tyvars_to_keep)
- (vcat [non_std_why clas,
+ 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")])
-
- bale_out err = addErrTc err `thenM_` returnM (Nothing, Nothing)
-
-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
-
-
-new_dfun_name clas tycon -- Just a simple wrapper
- = newDFunName clas [mkTyConApp tycon []] (getSrcLoc tycon)
- -- The type passed to newDFunName is only used to generate
- -- a suitable string; hence the empty type arg list
-
-------------------------------------------------------------------
-mkDataTypeEqn :: SrcSpan -> InstOrigin -> TyCon -> Class -> TcM DerivEqn
-mkDataTypeEqn loc orig tycon clas
- | clas `hasKey` typeableClassKey
- = -- The Typeable class is special in several ways
- -- data T a b = ... deriving( Typeable )
- -- gives
- -- instance Typeable2 T where ...
- -- Notice that:
- -- 1. There are no constraints in the instance
- -- 2. There are no type variables either
- -- 3. The actual class we want to generate isn't necessarily
- -- Typeable; it depends on the arity of the type
- do { real_clas <- tcLookupClass (typeableClassNames !! tyConArity tycon)
- ; dfun_name <- new_dfun_name real_clas tycon
- ; return (loc, orig, dfun_name, real_clas, tycon, [], []) }
-
- | otherwise
- = do { dfun_name <- new_dfun_name clas tycon
- ; return (loc, orig, dfun_name, clas, tycon, tyvars, constraints)
- }
- where
- tyvars = tyConTyVars tycon
- constraints = extra_constraints ++ ordinary_constraints
- extra_constraints = tyConStupidTheta tycon
- -- "extra_constraints": see note [Data decl contexts] above
-
- ordinary_constraints
- = [ mkClassPred clas [arg_ty]
- | data_con <- tyConDataCons tycon,
- arg_ty <- dataConInstOrigArgTys data_con (mkTyVarTys tyvars),
- not (isUnLiftedType arg_ty) -- No constraints for unlifted types?
- ]
-
-
-------------------------------------------------------------------
--- Check side conditions that dis-allow derivability for particular classes
--- This is *apart* from the newtype-deriving mechanism
-
-checkSideConditions :: Bool -> TyCon -> [TyVar] -> Class -> [TcType] -> Maybe SDoc
-checkSideConditions gla_exts tycon deriv_tvs clas tys
- | notNull deriv_tvs || notNull tys
- = Just ty_args_why -- e.g. deriving( Foo s )
- | otherwise
- = case [cond | (key,cond) <- sideConditions, key == getUnique clas] of
- [] -> Just (non_std_why clas)
- [cond] -> cond (gla_exts, tycon)
- other -> pprPanic "checkSideConditions" (ppr clas)
- where
- ty_args_why = quotes (ppr (mkClassPred clas tys)) <+> ptext SLIT("is not a class")
-
-non_std_why clas = quotes (ppr clas) <+> ptext SLIT("is not a derivable class")
-
-sideConditions :: [(Unique, Condition)]
-sideConditions
- = [ (eqClassKey, cond_std),
- (ordClassKey, cond_std),
- (readClassKey, cond_std),
- (showClassKey, cond_std),
- (enumClassKey, cond_std `andCond` cond_isEnumeration),
- (ixClassKey, cond_std `andCond` (cond_isEnumeration `orCond` cond_isProduct)),
- (boundedClassKey, cond_std `andCond` (cond_isEnumeration `orCond` cond_isProduct)),
- (typeableClassKey, cond_glaExts `andCond` cond_typeableOK),
- (dataClassKey, cond_glaExts `andCond` cond_std)
- ]
-
-type Condition = (Bool, TyCon) -> Maybe SDoc -- Nothing => OK
-
-orCond :: Condition -> Condition -> Condition
-orCond c1 c2 tc
- = case c1 tc of
- Nothing -> Nothing -- c1 succeeds
- Just x -> case c2 tc of -- c1 fails
- Nothing -> Nothing
- Just y -> Just (x $$ ptext SLIT(" and") $$ y)
- -- Both fail
-
-andCond c1 c2 tc = case c1 tc of
- Nothing -> c2 tc -- c1 succeeds
- Just x -> Just x -- c1 fails
-
-cond_std :: Condition
-cond_std (gla_exts, tycon)
- | any (not . isVanillaDataCon) data_cons = Just existential_why
- | null data_cons = Just no_cons_why
- | otherwise = Nothing
- where
- data_cons = tyConDataCons tycon
- no_cons_why = quotes (ppr tycon) <+> ptext SLIT("has no data constructors")
- existential_why = quotes (ppr tycon) <+> ptext SLIT("has non-Haskell-98 constructor(s)")
-
-cond_isEnumeration :: Condition
-cond_isEnumeration (gla_exts, tycon)
- | isEnumerationTyCon tycon = Nothing
- | otherwise = Just why
- where
- why = quotes (ppr tycon) <+> ptext SLIT("has non-nullary constructors")
-
-cond_isProduct :: Condition
-cond_isProduct (gla_exts, tycon)
- | isProductTyCon tycon = Nothing
- | otherwise = Just why
- where
- why = quotes (ppr tycon) <+> ptext SLIT("has more than one constructor")
-
-cond_typeableOK :: Condition
--- OK for Typeable class
--- Currently: (a) args all of kind *
--- (b) 7 or fewer args
-cond_typeableOK (gla_exts, tycon)
- | tyConArity tycon > 7 = Just too_many
- | not (all (isSubArgTypeKind . tyVarKind) (tyConTyVars tycon))
- = Just bad_kind
- | isFamInstTyCon tycon = Just fam_inst -- no Typable for family insts
- | otherwise = Nothing
- where
- too_many = quotes (ppr tycon) <+> ptext SLIT("has too many arguments")
- bad_kind = quotes (ppr tycon) <+>
- ptext SLIT("has arguments of kind other than `*'")
- fam_inst = quotes (ppr tycon) <+> ptext SLIT("is a type family")
-
-cond_glaExts :: Condition
-cond_glaExts (gla_exts, tycon) | gla_exts = Nothing
- | otherwise = Just why
- where
- why = ptext SLIT("You need -fglasgow-exts to derive an instance for this class")
\end{code}
+
%************************************************************************
%* *
\subsection[TcDeriv-fixpoint]{Finding the fixed point of \tr{deriving} equations}
-- This bunch is Absolutely minimal...
solveDerivEqns overlap_flag orig_eqns
- = iterateDeriv 1 initial_solutions
+ = do { traceTc (text "solveDerivEqns" <+> vcat (map pprDerivEqn orig_eqns))
+ ; iterateDeriv 1 initial_solutions }
where
-- The initial solutions for the equations claim that each
-- instance has an empty context; this solution is certainly
------------------------------------------------------------------
gen_soln :: DerivEqn -> TcM [PredType]
- gen_soln (loc, orig, _, clas, tc, tyvars, deriv_rhs)
+ gen_soln (loc, orig, _, tyvars, clas, inst_ty, deriv_rhs)
= setSrcSpan loc $
- do { let inst_tys = [origHead]
- ; theta <- addErrCtxt (derivInstCtxt1 clas inst_tys) $
- tcSimplifyDeriv orig tc tyvars deriv_rhs
+ 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
+
+ -- Check for a bizarre corner case, when the derived instance decl should
+ -- have form instance C a b => D (T a) where ...
+ -- Note that 'b' isn't a parameter of T. This gives rise to all sorts
+ -- of problems; in particular, it's hard to compare solutions for
+ -- equality when finding the fixpoint. So I just rule it out for now.
+ ; let tv_set = mkVarSet tyvars
+ weird_preds = [pred | pred <- theta, not (tyVarsOfPred pred `subVarSet` tv_set)]
+ ; mapM_ (addErrTc . badDerivedPred) weird_preds
+
-- 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
- where
- origHead = uncurry mkTyConApp (tyConOrigHead tc)
+ ; return (sortLe (<=) theta) } } -- Canonicalise before returning the solution
------------------------------------------------------------------
mk_inst_spec :: DerivEqn -> DerivSoln -> Instance
- mk_inst_spec (loc, orig, dfun_name, clas, tycon, tyvars, _) theta
+ mk_inst_spec (loc, orig, dfun_name, tyvars, clas, inst_ty, _) theta
= mkLocalInstance dfun overlap_flag
where
- dfun = mkDictFunId dfun_name tyvars theta clas [origHead]
- origHead = uncurry mkTyConApp (tyConOrigHead tycon)
+ dfun = mkDictFunId dfun_name tyvars theta clas [inst_ty]
extendLocalInstEnv :: [Instance] -> TcM a -> TcM a
-- Add new locally-defined instances; don't bother to check
(visible_tycon, tyArgs) = tcSplitTyConApp ty
-- In case of a family instance, we need to use the representation
- -- tycon (after all it has the data constructors)
- ; tycon <- if isOpenTyCon visible_tycon
- then tcLookupFamInst visible_tycon tyArgs
- else return visible_tycon
+ -- tycon (after all, it has the data constructors)
+ ; (tycon, _) <- tcLookupFamInst visible_tycon tyArgs
; let (meth_binds, aux_binds) = genDerivBinds clas fix_env tycon
-- Bring the right type variables into
\end{code}
\begin{code}
-derivingThingErr clas tys tycon ttys why
+derivingThingErr clas tys ty why
= sep [hsep [ptext SLIT("Can't make a derived instance of"),
quotes (ppr pred)],
nest 2 (parens why)]
where
- pred = mkClassPred clas (tys ++ [mkTyConApp tycon ttys])
+ pred = mkClassPred clas (tys ++ [ty])
-derivCtxt :: Name -> Maybe [LHsType Name] -> SDoc
-derivCtxt tycon mb_tys
- = ptext SLIT("When deriving instances for") <+> quotes typeInst
- where
- typeInst = case mb_tys of
- Nothing -> ppr tycon
- Just tys -> ppr tycon <+>
- hsep (map (pprParendHsType . unLoc) tys)
-
-derivInstCtxt1 clas inst_tys
- = ptext SLIT("When deriving the instance for") <+>
- quotes (pprClassPred clas inst_tys)
+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
+
+badDerivedPred pred
+ = vcat [ptext SLIT("Can't derive instances where the instance context mentions"),
+ ptext SLIT("type variables that are not data type parameters"),
+ nest 2 (ptext SLIT("Offending constraint:") <+> ppr pred)]
\end{code}
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