import Class
import Type
+import Coercion
import ErrUtils
import MkId
import DataCon
import NameSet
import TyCon
import TcType
+import BuildTyCl
+import BasicTypes
import Var
import VarSet
import PrelNames
import SrcLoc
+import UniqSupply
import Util
import ListSetOps
import Outputable
+import FastString
import Bag
-import Monad (unless)
+import Control.Monad
\end{code}
%************************************************************************
%* *
-\subsection[TcDeriv-intro]{Introduction to how we do deriving}
+ Overview
%* *
%************************************************************************
+Overall plan
+~~~~~~~~~~~~
+1. Convert the decls (i.e. data/newtype deriving clauses,
+ plus standalone deriving) to [EarlyDerivSpec]
+
+2. Infer the missing contexts for the Left DerivSpecs
+
+3. Add the derived bindings, generating InstInfos
+
+
+\begin{code}
+-- DerivSpec is purely local to this module
+data DerivSpec = DS { ds_loc :: SrcSpan
+ , ds_orig :: CtOrigin
+ , ds_name :: Name
+ , ds_tvs :: [TyVar]
+ , ds_theta :: ThetaType
+ , 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 Name is the name for the DFun we'll build
+ -- The tyvars bind all the variables in the theta
+ -- For type families, the tycon in
+ -- in ds_tys is the *family* tycon
+ -- in ds_tc, ds_tc_args is the *representation* tycon
+ -- For non-family tycons, both are the same
+
+ -- ds_newtype = True <=> Newtype deriving
+ -- False <=> Vanilla deriving
+\end{code}
+
+Example:
+
+ newtype instance T [a] = MkT (Tree a) deriving( C s )
+==>
+ axiom T [a] = :RTList a
+ axiom :RTList a = Tree a
+
+ DS { ds_tvs = [a,s], ds_cls = C, ds_tys = [s, T [a]]
+ , ds_tc = :RTList, ds_tc_args = [a]
+ , ds_newtype = True }
+
+\begin{code}
+type DerivContext = Maybe ThetaType
+ -- Nothing <=> Vanilla deriving; infer the context of the instance decl
+ -- Just theta <=> Standalone deriving: context supplied by programmer
+
+type EarlyDerivSpec = Either DerivSpec DerivSpec
+ -- Left ds => the context for the instance should be inferred
+ -- In this case ds_theta is the list of all the
+ -- constraints needed, such as (Eq [a], Eq a)
+ -- The inference process is to reduce this to a
+ -- simpler form (e.g. Eq a)
+ --
+ -- Right ds => the exact context for the instance is supplied
+ -- by the programmer; it is ds_theta
+
+pprDerivSpec :: DerivSpec -> SDoc
+pprDerivSpec (DS { ds_loc = l, ds_name = n, ds_tvs = tvs,
+ ds_cls = c, ds_tys = tys, ds_theta = rhs })
+ = parens (hsep [ppr l, ppr n, ppr tvs, ppr c, ppr tys]
+ <+> equals <+> ppr rhs)
+
+instance Outputable DerivSpec where
+ ppr = pprDerivSpec
+\end{code}
+
+
+Inferring missing contexts
+~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider
data T a b = C1 (Foo a) (Bar b)
So, here are the synonyms for the ``equation'' structures:
-\begin{code}
-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}
-
-
-[Data decl contexts] A note about contexts on data decls
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Note [Data decl contexts]
+~~~~~~~~~~~~~~~~~~~~~~~~~
Consider
data (RealFloat a) => Complex a = !a :+ !a deriving( Read )
gives rise to the constraints for that context -- or at least the thinned
version. So now all classes are "offending".
-[Newtype deriving]
-~~~~~~~~~~~~~~~~~~
+Note [Newtype deriving]
+~~~~~~~~~~~~~~~~~~~~~~~
Consider this:
class C a b
instance C [a] Char
instance C [a] Char => C [a] T where ...
+Note [Newtype deriving superclasses]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+(See also Trac #1220 for an interesting exchange on newtype
+deriving and superclasses.)
+The 'tys' here come from the partial application in the deriving
+clause. The last arg is the new instance type.
+
+We must pass the superclasses; the newtype might be an instance
+of them in a different way than the representation type
+E.g. newtype Foo a = Foo a deriving( Show, Num, Eq )
+Then the Show instance is not done via isomorphism; it shows
+ Foo 3 as "Foo 3"
+The Num instance is derived via isomorphism, but the Show superclass
+dictionary must the Show instance for Foo, *not* the Show dictionary
+gotten from the Num dictionary. So we must build a whole new dictionary
+not just use the Num one. The instance we want is something like:
+ instance (Num a, Show (Foo a), Eq (Foo a)) => Num (Foo a) where
+ (+) = ((+)@a)
+ ...etc...
+There may be a coercion needed which we get from the tycon for the newtype
+when the dict is constructed in TcInstDcls.tcInstDecl2
+
+
+Note [Unused constructors and deriving clauses]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+See Trac #3221. Consider
+ data T = T1 | T2 deriving( Show )
+Are T1 and T2 unused? Well, no: the deriving clause expands to mention
+both of them. So we gather defs/uses from deriving just like anything else.
%************************************************************************
%* *
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
+ -> TcM ([InstInfo Name] -- The generated "instance decls"
+ ,HsValBinds Name -- Extra generated top-level bindings
+ ,DefUses
+ ,[TyCon] -- Extra generated top-level types
+ ,[TyCon]) -- Extra generated type family instances
tcDeriving tycl_decls inst_decls deriv_decls
- = recoverM (returnM ([], emptyValBindsOut)) $
+ = recoverM (return ([], emptyValBindsOut, emptyDUs, [], [])) $
do { -- Fish the "deriving"-related information out of the TcEnv
- -- and make the necessary "equations".
- ; (ordinary_eqns, newtype_inst_info)
- <- makeDerivEqns tycl_decls inst_decls deriv_decls
-
- ; (ordinary_inst_info, deriv_binds)
- <- extendLocalInstEnv (map iSpec newtype_inst_info) $
- deriveOrdinaryStuff ordinary_eqns
- -- Add the newtype-derived instances to the inst env
- -- before tacking the "ordinary" ones
-
- ; let inst_info = newtype_inst_info ++ ordinary_inst_info
-
- -- If we are compiling a hs-boot file,
- -- don't generate any derived bindings
- ; is_boot <- tcIsHsBoot
- ; if is_boot then
- return (inst_info, emptyValBindsOut)
- else do
- {
-
- -- Generate the generic to/from functions from each type declaration
- ; gen_binds <- mkGenericBinds tycl_decls
-
- -- Rename these extra bindings, discarding warnings about unused bindings etc
- -- Type signatures in patterns are used in the generic binds
- ; rn_binds
- <- discardWarnings $
- setOptM Opt_PatternSignatures $
- do
- { (rn_deriv, _dus1) <- rnTopBinds (ValBindsIn deriv_binds [])
- ; (rn_gen, dus_gen) <- rnTopBinds (ValBindsIn gen_binds [])
- ; keepAliveSetTc (duDefs dus_gen) -- Mark these guys to
- -- be kept alive
- ; return (rn_deriv `plusHsValBinds` rn_gen) }
+ -- And make the necessary "equations".
+ is_boot <- tcIsHsBoot
+ ; traceTc "tcDeriving" (ppr is_boot)
+ ; (early_specs, genericsExtras)
+ <- makeDerivSpecs is_boot tycl_decls inst_decls deriv_decls
+ ; let (repMetaTys, repTyCons, metaInsts) = unzip3 genericsExtras
+
+ ; overlap_flag <- getOverlapFlag
+ ; let (infer_specs, given_specs) = splitEithers early_specs
+ ; insts1 <- mapM (genInst True overlap_flag) given_specs
+
+ ; final_specs <- extendLocalInstEnv (map (iSpec . fst) insts1) $
+ inferInstanceContexts overlap_flag infer_specs
+
+ ; insts2 <- mapM (genInst False overlap_flag) final_specs
+ -- We no longer generate the old generic to/from functions
+ -- from each type declaration, so this is emptyBag
+ ; gen_binds <- return emptyBag -- mkGenericBinds is_boot tycl_decls
+
+ ; (inst_info, rn_binds, rn_dus)
+ <- renameDeriv is_boot gen_binds (insts1 ++ insts2 ++ concat metaInsts)
; dflags <- getDOpts
- ; ioToTcRn (dumpIfSet_dyn dflags Opt_D_dump_deriv "Derived instances"
- (ddump_deriving inst_info rn_binds))
+ ; liftIO (dumpIfSet_dyn dflags Opt_D_dump_deriv "Derived instances"
+ (ddump_deriving inst_info rn_binds repMetaTys repTyCons metaInsts))
+{-
+ ; when (not (null inst_info)) $
+ dumpDerivingInfo (ddump_deriving inst_info rn_binds)
+-}
+ ; return ( inst_info, rn_binds, rn_dus
+ , concat (map metaTyCons2TyCons repMetaTys), repTyCons) }
+ where
+ ddump_deriving :: [InstInfo Name] -> HsValBinds Name
+ -> [MetaTyCons] -- ^ Empty data constructors
+ -> [TyCon] -- ^ Rep type family instances
+ -> [[(InstInfo RdrName, DerivAuxBinds)]]
+ -- ^ Instances for the repMetaTys
+ -> SDoc
+ ddump_deriving inst_infos extra_binds repMetaTys repTyCons metaInsts
+ = hang (ptext (sLit "Derived instances"))
+ 2 (vcat (map (\i -> pprInstInfoDetails i $$ text "") inst_infos)
+ $$ ppr extra_binds)
+ $$ hangP "Generic representation" (
+ hangP "Generated datatypes for meta-information"
+ (vcat (map ppr repMetaTys))
+ -- The Outputable instance for TyCon unfortunately only prints the name...
+ $$ hangP "Representation types"
+ (vcat (map ppr repTyCons))
+ $$ hangP "Meta-information instances"
+ (vcat (map (pprInstInfoDetails . fst) (concat metaInsts))))
+
+ hangP s x = text "" $$ hang (ptext (sLit s)) 2 x
+
+
+renameDeriv :: Bool -> LHsBinds RdrName
+ -> [(InstInfo RdrName, DerivAuxBinds)]
+ -> TcM ([InstInfo Name], HsValBinds Name, DefUses)
+renameDeriv is_boot gen_binds insts
+ | is_boot -- If we are compiling a hs-boot file, don't generate any derived bindings
+ -- The inst-info bindings will all be empty, but it's easier to
+ -- just use rn_inst_info to change the type appropriately
+ = do { (rn_inst_infos, fvs) <- mapAndUnzipM rn_inst_info inst_infos
+ ; return (rn_inst_infos, emptyValBindsOut, usesOnly (plusFVs fvs)) }
+
+ | otherwise
+ = discardWarnings $ -- Discard warnings about unused bindings etc
+ do { (rn_gen, dus_gen) <- setOptM Opt_ScopedTypeVariables $ -- Type signatures in patterns
+ -- are used in the generic binds
+ rnTopBinds (ValBindsIn gen_binds [])
+ ; keepAliveSetTc (duDefs dus_gen) -- Mark these guys to be kept alive
+
+ -- Generate and rename any extra not-one-inst-decl-specific binds,
+ -- notably "con2tag" and/or "tag2con" functions.
+ -- Bring those names into scope before renaming the instances themselves
+ ; loc <- getSrcSpanM -- Generic loc for shared bindings
+ ; let (aux_binds, aux_sigs) = unzip $ map (genAuxBind loc) $
+ rm_dups [] $ concat deriv_aux_binds
+ aux_val_binds = ValBindsIn (listToBag aux_binds) aux_sigs
+ ; rn_aux_lhs <- rnTopBindsLHS emptyFsEnv aux_val_binds
+ ; bindLocalNames (collectHsValBinders rn_aux_lhs) $
+ do { (rn_aux, dus_aux) <- rnTopBindsRHS rn_aux_lhs
+ ; (rn_inst_infos, fvs_insts) <- mapAndUnzipM rn_inst_info inst_infos
+ ; return (rn_inst_infos, rn_aux `plusHsValBinds` rn_gen,
+ dus_gen `plusDU` dus_aux `plusDU` usesOnly (plusFVs fvs_insts)) } }
- ; returnM (inst_info, rn_binds)
- }}
where
- ddump_deriving :: [InstInfo] -> HsValBinds Name -> SDoc
- ddump_deriving inst_infos extra_binds
- = vcat (map pprInstInfoDetails inst_infos) $$ ppr extra_binds
-
------------------------------------------
-deriveOrdinaryStuff [] -- Short cut
- = returnM ([], emptyLHsBinds)
-
-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.
- overlap_flag <- getOverlapFlag
- ; inst_specs <- solveDerivEqns overlap_flag eqns
-
- -- Generate the InstInfo for each dfun,
- -- plus any auxiliary bindings it needs
- ; (inst_infos, aux_binds_s) <- mapAndUnzipM genInst inst_specs
-
- -- Generate any extra not-one-inst-decl-specific binds,
- -- notably "con2tag" and/or "tag2con" functions.
- ; extra_binds <- genTaggeryBinds inst_infos
-
- -- Done
- ; returnM (map fst inst_infos,
- unionManyBags (extra_binds : aux_binds_s))
- }
-
------------------------------------------
-mkGenericBinds tycl_decls
- = do { tcs <- mapM tcLookupTyCon
- [ tc_name |
- L _ (TyData { tcdLName = L _ tc_name }) <- tycl_decls]
- -- We are only interested in the data type declarations
- ; return (unionManyBags [ mkTyConGenericBinds tc |
- tc <- tcs, tyConHasGenerics tc ]) }
- -- And then only in the ones whose 'has-generics' flag is on
+ (inst_infos, deriv_aux_binds) = unzip insts
+
+ -- Remove duplicate requests for auxilliary bindings
+ rm_dups acc [] = acc
+ rm_dups acc (b:bs) | any (isDupAux b) acc = rm_dups acc bs
+ | otherwise = rm_dups (b:acc) bs
+
+
+ rn_inst_info :: InstInfo RdrName -> TcM (InstInfo Name, FreeVars)
+ rn_inst_info info@(InstInfo { iBinds = NewTypeDerived coi tc })
+ = return ( info { iBinds = NewTypeDerived coi tc }
+ , mkFVs (map dataConName (tyConDataCons tc)))
+ -- See Note [Newtype deriving and unused constructors]
+
+ rn_inst_info inst_info@(InstInfo { iSpec = inst, iBinds = VanillaInst binds sigs standalone_deriv })
+ = -- Bring the right type variables into
+ -- scope (yuk), and rename the method binds
+ ASSERT( null sigs )
+ bindLocalNames (map Var.varName tyvars) $
+ do { (rn_binds, fvs) <- rnMethodBinds clas_nm (\_ -> []) binds
+ ; let binds' = VanillaInst rn_binds [] standalone_deriv
+ ; return (inst_info { iBinds = binds' }, fvs) }
+ where
+ (tyvars,_, clas,_) = instanceHead inst
+ clas_nm = className clas
\end{code}
+Note [Newtype deriving and unused constructors]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Consider this (see Trac #1954):
-%************************************************************************
-%* *
-\subsection[TcDeriv-eqns]{Forming the equations}
-%* *
-%************************************************************************
-
-@makeDerivEqns@ fishes around to find the info about needed derived
-instances. Complicating factors:
-\begin{itemize}
-\item
-We can only derive @Enum@ if the data type is an enumeration
-type (all nullary data constructors).
+ module Bug(P) where
+ newtype P a = MkP (IO a) deriving Monad
-\item
-We can only derive @Ix@ if the data type is an enumeration {\em
-or} has just one data constructor (e.g., tuples).
-\end{itemize}
+If you compile with -fwarn-unused-binds you do not expect the warning
+"Defined but not used: data consructor MkP". Yet the newtype deriving
+code does not explicitly mention MkP, but it should behave as if you
+had written
+ instance Monad P where
+ return x = MkP (return x)
+ ...etc...
-[See Appendix~E in the Haskell~1.2 report.] This code here deals w/
-all those.
+So we want to signal a user of the data constructor 'MkP'. That's
+what we do in rn_inst_info, and it's the only reason we have the TyCon
+stored in NewTypeDerived.
-Note [Newtype deriving superclasses]
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-The 'tys' here come from the partial application in the deriving
-clause. The last arg is the new instance type.
-We must pass the superclasses; the newtype might be an instance
-of them in a different way than the representation type
-E.g. newtype Foo a = Foo a deriving( Show, Num, Eq )
-Then the Show instance is not done via isomorphism; it shows
- Foo 3 as "Foo 3"
-The Num instance is derived via isomorphism, but the Show superclass
-dictionary must the Show instance for Foo, *not* the Show dictionary
-gotten from the Num dictionary. So we must build a whole new dictionary
-not just use the Num one. The instance we want is something like:
- instance (Num a, Show (Foo a), Eq (Foo a)) => Num (Foo a) where
- (+) = ((+)@a)
- ...etc...
-There may be a coercion needed which we get from the tycon for the newtype
-when the dict is constructed in TcInstDcls.tcInstDecl2
+%************************************************************************
+%* *
+ From HsSyn to DerivSpec
+%* *
+%************************************************************************
+@makeDerivSpecs@ fishes around to find the info about needed derived instances.
\begin{code}
-makeDerivEqns :: [LTyClDecl Name]
- -> [LInstDecl Name]
- -> [LDerivDecl Name]
- -> TcM ([DerivEqn], -- Ordinary derivings
- [InstInfo]) -- Special newtype derivings
-
-makeDerivEqns tycl_decls inst_decls deriv_decls
- = do { eqns1 <- mapM deriveTyData $
- 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]) }
+-- Make the "extras" for the generic representation
+mkGenDerivExtras :: TyCon
+ -> TcRn (MetaTyCons, TyCon, [(InstInfo RdrName, DerivAuxBinds)])
+mkGenDerivExtras tc = do
+ { (metaTyCons, rep0TyInst) <- genGenericRepExtras tc
+ ; metaInsts <- genDtMeta (tc, metaTyCons)
+ ; return (metaTyCons, rep0TyInst, metaInsts) }
+
+makeDerivSpecs :: Bool
+ -> [LTyClDecl Name]
+ -> [LInstDecl Name]
+ -> [LDerivDecl Name]
+ -> TcM ( [EarlyDerivSpec]
+ , [(MetaTyCons, TyCon, [(InstInfo RdrName, DerivAuxBinds)])])
+makeDerivSpecs is_boot tycl_decls inst_decls deriv_decls
+ | is_boot -- No 'deriving' at all in hs-boot files
+ = do { mapM_ add_deriv_err deriv_locs
+ ; return ([],[]) }
+ | otherwise
+ = do { eqns1 <- mapAndRecoverM deriveTyData all_tydata
+ ; eqns2 <- mapAndRecoverM deriveStandalone deriv_decls
+
+ -- Generic representation stuff: we might need to add some "extras"
+ -- to the instances
+ ; xDerRep <- getDOpts >>= return . xopt Opt_DeriveGeneric
+ ; generic_extras_deriv <- if not xDerRep
+ -- No extras if the flag is off
+ then (return [])
+ else do {
+ let allTyNames = [ tcdName d | L _ d <- tycl_decls, isDataDecl d ]
+ -- Select only those types that derive Generic
+ ; let sel_tydata = [ tcdName t | (L _ c, L _ t) <- all_tydata
+ , getClassName c == Just genClassName ]
+ ; let sel_deriv_decls = catMaybes [ getTypeName t
+ | L _ (DerivDecl (L _ t)) <- deriv_decls
+ , getClassName t == Just genClassName ]
+ ; derTyDecls <- mapM tcLookupTyCon $
+ filter (needsExtras xDerRep
+ (sel_tydata ++ sel_deriv_decls)) allTyNames
+ -- We need to generate the extras to add to what has
+ -- already been derived
+ ; {- pprTrace "sel_tydata" (ppr sel_tydata) $
+ pprTrace "sel_deriv_decls" (ppr sel_deriv_decls) $
+ pprTrace "derTyDecls" (ppr derTyDecls) $
+ pprTrace "deriv_decls" (ppr deriv_decls) $ -}
+ mapM mkGenDerivExtras derTyDecls }
+
+ -- Merge and return
+ ; return ( eqns1 ++ eqns2, generic_extras_deriv) }
where
- extractTyDataPreds decls =
- [(p, d) | d@(L _ (TyData {tcdDerivs = Just preds})) <- decls, p <- preds]
-
+ -- We need extras if the flag DeriveGeneric is on and this type is
+ -- deriving Generic
+ needsExtras xDerRep tydata tc_name = xDerRep && tc_name `elem` tydata
+
+ -- Extracts the name of the class in the deriving
+ getClassName :: HsType Name -> Maybe Name
+ getClassName (HsForAllTy _ _ _ (L _ n)) = getClassName n
+ getClassName (HsPredTy (HsClassP n _)) = Just n
+ getClassName _ = Nothing
+
+ -- Extracts the name of the type in the deriving
+ -- This function (and also getClassName above) is not really nice, and I
+ -- might not have covered all possible cases. I wonder if there is no easier
+ -- way to extract class and type name from a LDerivDecl...
+ getTypeName :: HsType Name -> Maybe Name
+ getTypeName (HsForAllTy _ _ _ (L _ n)) = getTypeName n
+ getTypeName (HsTyVar n) = Just n
+ getTypeName (HsOpTy _ (L _ n) _) = Just n
+ getTypeName (HsPredTy (HsClassP _ [L _ n])) = getTypeName n
+ getTypeName (HsAppTy (L _ n) _) = getTypeName n
+ getTypeName (HsParTy (L _ n)) = getTypeName n
+ getTypeName (HsKindSig (L _ n) _) = getTypeName n
+ getTypeName _ = Nothing
+
+ extractTyDataPreds decls
+ = [(p, d) | d@(L _ (TyData {tcdDerivs = Just preds})) <- decls, p <- preds]
+
+ all_tydata :: [(LHsType Name, LTyClDecl Name)]
+ -- Derived predicate paired with its data type declaration
+ all_tydata = extractTyDataPreds (instDeclATs inst_decls ++ tycl_decls)
+
+ deriv_locs = map (getLoc . snd) all_tydata
+ ++ map getLoc deriv_decls
+
+ add_deriv_err loc = setSrcSpan loc $
+ addErr (hang (ptext (sLit "Deriving not permitted in hs-boot file"))
+ 2 (ptext (sLit "Use an instance declaration instead")))
------------------------------------------------------------------
-deriveStandalone :: LDerivDecl Name -> TcM (Maybe DerivEqn, Maybe InstInfo)
+deriveStandalone :: LDerivDecl Name -> TcM EarlyDerivSpec
-- Standalone deriving declarations
--- e.g. derive instance Show T
+-- e.g. deriving instance Show a => Show (T a)
-- 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 }
+ do { traceTc "Standalone deriving decl for" (ppr deriv_ty)
+ ; (tvs, theta, cls, inst_tys) <- tcHsInstHead deriv_ty
+ ; traceTc "Standalone deriving;" $ vcat
+ [ text "tvs:" <+> ppr tvs
+ , text "theta:" <+> ppr theta
+ , text "cls:" <+> ppr cls
+ , text "tys:" <+> ppr inst_tys ]
+ ; checkValidInstance deriv_ty tvs theta cls inst_tys
+ -- C.f. TcInstDcls.tcLocalInstDecl1
+
+ ; let cls_tys = take (length inst_tys - 1) inst_tys
+ inst_ty = last inst_tys
+ ; traceTc "Standalone deriving:" $ vcat
+ [ text "class:" <+> ppr cls
+ , text "class types:" <+> ppr cls_tys
+ , text "type:" <+> ppr inst_ty ]
+ ; mkEqnHelp StandAloneDerivOrigin tvs cls cls_tys inst_ty
+ (Just theta) }
------------------------------------------------------------------
-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
+deriveTyData :: (LHsType Name, LTyClDecl Name) -> TcM EarlyDerivSpec
+deriveTyData (L loc deriv_pred, L _ decl@(TyData { tcdLName = L _ tycon_name,
+ tcdTyVars = tv_names,
+ tcdTyPats = ty_pats }))
+ = setSrcSpan loc $ -- Use the location of the 'deriving' item
+ tcAddDeclCtxt decl $
+ do { (tvs, tc, tc_args) <- get_lhs ty_pats
; 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 } }
-deriveTyData (deriv_pred, other_decl)
+
+ -- Given data T a b c = ... deriving( C d ),
+ -- we want to drop type variables from T so that (C d (T a)) is well-kinded
+ ; let cls_tyvars = classTyVars cls
+ kind = tyVarKind (last cls_tyvars)
+ (arg_kinds, _) = splitKindFunTys kind
+ n_args_to_drop = length arg_kinds
+ n_args_to_keep = tyConArity tc - n_args_to_drop
+ args_to_drop = drop n_args_to_keep tc_args
+ inst_ty = mkTyConApp tc (take n_args_to_keep tc_args)
+ inst_ty_kind = typeKind inst_ty
+ dropped_tvs = mkVarSet (mapCatMaybes getTyVar_maybe args_to_drop)
+ univ_tvs = (mkVarSet tvs `extendVarSetList` deriv_tvs)
+ `minusVarSet` dropped_tvs
+
+ -- Check that the result really is well-kinded
+ ; checkTc (n_args_to_keep >= 0 && (inst_ty_kind `eqKind` kind))
+ (derivingKindErr tc cls cls_tys kind)
+
+ ; checkTc (sizeVarSet dropped_tvs == n_args_to_drop && -- (a)
+ tyVarsOfTypes (inst_ty:cls_tys) `subVarSet` univ_tvs) -- (b)
+ (derivingEtaErr cls cls_tys inst_ty)
+ -- Check that
+ -- (a) The data type can be eta-reduced; eg reject:
+ -- data instance T a a = ... deriving( Monad )
+ -- (b) The type class args do not mention any of the dropped type
+ -- variables
+ -- newtype T a s = ... deriving( ST s )
+
+ -- Type families can't be partially applied
+ -- e.g. newtype instance T Int a = MkT [a] deriving( Monad )
+ -- Note [Deriving, type families, and partial applications]
+ ; checkTc (not (isFamilyTyCon tc) || n_args_to_drop == 0)
+ (typeFamilyPapErr tc cls cls_tys inst_ty)
+
+ ; mkEqnHelp DerivOrigin (varSetElems univ_tvs) cls cls_tys inst_ty Nothing } }
+ where
+ -- Tiresomely we must figure out the "lhs", which is awkward for type families
+ -- E.g. data T a b = .. deriving( Eq )
+ -- Here, the lhs is (T a b)
+ -- data instance TF Int b = ... deriving( Eq )
+ -- Here, the lhs is (TF Int b)
+ -- But if we just look up the tycon_name, we get is the *family*
+ -- tycon, but not pattern types -- they are in the *rep* tycon.
+ get_lhs Nothing = do { tc <- tcLookupTyCon tycon_name
+ ; let tvs = tyConTyVars tc
+ ; return (tvs, tc, mkTyVarTys tvs) }
+ get_lhs (Just pats) = do { let hs_app = nlHsTyConApp tycon_name pats
+ ; (tvs, tc_app) <- tcHsQuantifiedType tv_names hs_app
+ ; let (tc, tc_args) = tcSplitTyConApp tc_app
+ ; return (tvs, tc, tc_args) }
+
+deriveTyData _other
= panic "derivTyData" -- Caller ensures that only TyData can happen
+\end{code}
-------------------------------------------------------------------
-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) <- tcLookupFamInstExact tycon full_tc_args
+Note [Deriving, type families, and partial applications]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+When there are no type families, it's quite easy:
- ; mayDeriveDataTypeable <- doptM Opt_DeriveDataTypeable
- ; newtype_deriving <- doptM Opt_GeneralizedNewtypeDeriving
- ; overlap_flag <- getOverlapFlag
+ newtype S a = MkS [a]
+ -- :CoS :: S ~ [] -- Eta-reduced
- -- 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 mayDeriveDataTypeable full_tvs cls cls_tys
- tycon full_tc_args rep_tc rep_tc_args
- else
- mkNewTypeEqn orig mayDeriveDataTypeable newtype_deriving 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")))
+ instance Eq [a] => Eq (S a) -- by coercion sym (Eq (:CoS a)) : Eq [a] ~ Eq (S a)
+ instance Monad [] => Monad S -- by coercion sym (Monad :CoS) : Monad [] ~ Monad S
-baleOut err = addErrTc err >> returnM (Nothing, Nothing)
-\end{code}
+When type familes are involved it's trickier:
+
+ data family T a b
+ newtype instance T Int a = MkT [a] deriving( Eq, Monad )
+ -- :RT is the representation type for (T Int a)
+ -- :CoF:R1T a :: T Int a ~ :RT a -- Not eta reduced
+ -- :Co:R1T :: :RT ~ [] -- Eta-reduced
-Auxiliary lookup wrapper which requires that looked up family instances are
-not type instances.
+ instance Eq [a] => Eq (T Int a) -- easy by coercion
+ instance Monad [] => Monad (T Int) -- only if we can eta reduce???
+
+The "???" bit is that we don't build the :CoF thing in eta-reduced form
+Henc the current typeFamilyPapErr, even though the instance makes sense.
+After all, we can write it out
+ instance Monad [] => Monad (T Int) -- only if we can eta reduce???
+ return x = MkT [x]
+ ... etc ...
\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
- }
-
+mkEqnHelp :: CtOrigin -> [TyVar] -> Class -> [Type] -> Type
+ -> DerivContext -- Just => context supplied (standalone deriving)
+ -- Nothing => context inferred (deriving on data decl)
+ -> TcRn EarlyDerivSpec
+-- Make the EarlyDerivSpec for an instance
+-- forall tvs. theta => cls (tys ++ [ty])
+-- where the 'theta' is optional (that's the Maybe part)
+-- Assumes that this declaration is well-kinded
+
+mkEqnHelp orig tvs cls cls_tys tc_app mtheta
+ | Just (tycon, tc_args) <- tcSplitTyConApp_maybe tc_app
+ , isAlgTyCon tycon -- Check for functions, primitive types etc
+ = mk_alg_eqn tycon tc_args
+ | otherwise
+ = failWithTc (derivingThingErr False cls cls_tys tc_app
+ (ptext (sLit "The last argument of the instance must be a data or newtype application")))
+
+ where
+ bale_out msg = failWithTc (derivingThingErr False cls cls_tys tc_app msg)
+
+ mk_alg_eqn tycon tc_args
+ | className cls `elem` typeableClassNames
+ = do { dflags <- getDOpts
+ ; case checkTypeableConditions (dflags, tycon) of
+ Just err -> bale_out err
+ Nothing -> mk_typeable_eqn orig tvs cls tycon tc_args mtheta }
+
+ | isDataFamilyTyCon tycon
+ , length tc_args /= tyConArity tycon
+ = bale_out (ptext (sLit "Unsaturated data family application"))
+
+ | otherwise
+ = do { (rep_tc, rep_tc_args) <- tcLookupDataFamInst tycon tc_args
+ -- Be careful to test rep_tc here: in the case of families,
+ -- we want to check the instance tycon, not the family tycon
+
+ -- For standalone deriving (mtheta /= Nothing),
+ -- check that all the data constructors are in scope.
+ ; rdr_env <- getGlobalRdrEnv
+ ; let hidden_data_cons = isAbstractTyCon rep_tc ||
+ any not_in_scope (tyConDataCons rep_tc)
+ not_in_scope dc = null (lookupGRE_Name rdr_env (dataConName dc))
+ ; unless (isNothing mtheta || not hidden_data_cons)
+ (bale_out (derivingHiddenErr tycon))
+
+ ; dflags <- getDOpts
+ ; if isDataTyCon rep_tc then
+ mkDataTypeEqn orig dflags tvs cls cls_tys
+ tycon tc_args rep_tc rep_tc_args mtheta
+ else
+ mkNewTypeEqn orig dflags tvs cls cls_tys
+ tycon tc_args rep_tc rep_tc_args mtheta }
\end{code}
%************************************************************************
\begin{code}
-mkDataTypeEqn orig mayDeriveDataTypeable tvs cls cls_tys
- tycon tc_args rep_tc rep_tc_args
- | Just err <- checkSideConditions mayDeriveDataTypeable cls cls_tys rep_tc
+mkDataTypeEqn :: CtOrigin
+ -> 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
+ -> DerivContext -- 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 dflags mtheta cls cls_tys rep_tc of
-- NB: pass the *representation* tycon to checkSideConditions
- = 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
+ CanDerive -> go_for_it
+ NonDerivableClass -> bale_out (nonStdErr cls)
+ DerivableClassError msg -> bale_out msg
+ where
+ go_for_it = mk_data_eqn orig tvs cls tycon tc_args rep_tc rep_tc_args mtheta
+ bale_out msg = failWithTc (derivingThingErr False cls cls_tys (mkTyConApp tycon tc_args) msg)
+
+mk_data_eqn :: CtOrigin -> [TyVar] -> Class
+ -> TyCon -> [TcType] -> TyCon -> [TcType] -> DerivContext
+ -> TcM EarlyDerivSpec
+mk_data_eqn orig tvs cls tycon tc_args rep_tc rep_tc_args mtheta
+ = do { dfun_name <- new_dfun_name cls tycon
+ ; loc <- getSrcSpanM
+ ; 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` inferred_constraints
+ , ds_newtype = False }
+
+ ; return (if isJust mtheta then Right spec -- Specified context
+ else Left spec) } -- Infer context
+
+----------------------
+mk_typeable_eqn :: CtOrigin -> [TyVar] -> Class
+ -> TyCon -> [TcType] -> DerivContext
+ -> TcM EarlyDerivSpec
+mk_typeable_eqn orig tvs cls tycon tc_args mtheta
+ -- The Typeable class is special in several ways
-- data T a b = ... deriving( Typeable )
-- gives
-- instance Typeable2 T where ...
-- 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 [], []) }
-
+ | isNothing mtheta -- deriving on a data type decl
+ = do { checkTc (cls `hasKey` typeableClassKey)
+ (ptext (sLit "Use deriving( Typeable ) on a data type declaration"))
+ ; real_cls <- tcLookupClass (typeableClassNames !! tyConArity tycon)
+ ; mk_typeable_eqn orig tvs real_cls tycon [] (Just []) }
+
+ | otherwise -- standaone deriving
+ = do { checkTc (null tc_args)
+ (ptext (sLit "Derived typeable instance must be of form (Typeable")
+ <> int (tyConArity tycon) <+> ppr tycon <> rparen)
+ ; dfun_name <- new_dfun_name cls tycon
+ ; 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 = tycon, ds_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 _ cls inst_tys rep_tc rep_tc_args
+ -- Generic constraints are easy
+ | cls `hasKey` genClassKey
+ = []
+ -- The others are a bit more complicated
| otherwise
- = do { dfun_name <- new_dfun_name cls tycon
- ; 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?
-
- 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)
- }
+ = 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 Data constraints
+ -- The Data class (only) requires that for
+ -- instance (...) => Data (T t1 t2)
+ -- IF t1:*, t2:*
+ -- THEN (Data t1, Data t2) are among the (...) constraints
+ -- Reason: when the IF holds, we generate a method
+ -- dataCast2 f = gcast2 f
+ -- and we need the Data constraints to typecheck the method
+ extra_constraints
+ | cls `hasKey` dataClassKey
+ , all (isLiftedTypeKind . typeKind) rep_tc_args
+ = [mkClassPred cls [ty] | ty <- rep_tc_args]
+ | otherwise
+ = []
------------------------------------------------------------------
-- Check side conditions that dis-allow derivability for particular classes
-- the data constructors - but we need to be careful to fall back to the
-- family tycon (with indexes) in error messages.
-checkSideConditions :: Bool -> Class -> [TcType] -> TyCon -> Maybe SDoc
-checkSideConditions mayDeriveDataTypeable cls cls_tys rep_tc
- | 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 (mayDeriveDataTypeable, rep_tc)
- other -> pprPanic "checkSideConditions" (ppr cls)
+data DerivStatus = CanDerive
+ | DerivableClassError SDoc -- Standard class, but can't do it
+ | NonDerivableClass -- Non-standard class
+
+checkSideConditions :: DynFlags -> DerivContext -> Class -> [TcType] -> TyCon -> DerivStatus
+checkSideConditions dflags mtheta cls cls_tys rep_tc
+ | Just cond <- sideConditions mtheta cls
+ = case (cond (dflags, rep_tc)) of
+ Just err -> DerivableClassError err -- Class-specific error
+ Nothing | null cls_tys -> CanDerive -- All derivable classes are unary, so
+ -- cls_tys (the type args other than last)
+ -- should be null
+ | otherwise -> DerivableClassError ty_args_why -- e.g. deriving( Eq s )
+ | otherwise = NonDerivableClass -- Not a standard class
+ where
+ ty_args_why = quotes (ppr (mkClassPred cls cls_tys)) <+> ptext (sLit "is not a class")
+
+checkTypeableConditions :: Condition
+checkTypeableConditions = checkFlag Opt_DeriveDataTypeable `andCond` cond_typeableOK
+
+nonStdErr :: Class -> SDoc
+nonStdErr cls = quotes (ppr cls) <+> ptext (sLit "is not a derivable class")
+
+sideConditions :: DerivContext -> Class -> Maybe Condition
+sideConditions mtheta 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 (checkFlag Opt_DeriveDataTypeable `andCond`
+ cond_std `andCond` cond_noUnliftedArgs)
+ | cls_key == functorClassKey = Just (checkFlag Opt_DeriveFunctor `andCond`
+ cond_functorOK True) -- NB: no cond_std!
+ | cls_key == foldableClassKey = Just (checkFlag Opt_DeriveFoldable `andCond`
+ cond_functorOK False) -- Functor/Fold/Trav works ok for rank-n types
+ | cls_key == traversableClassKey = Just (checkFlag Opt_DeriveTraversable `andCond`
+ cond_functorOK False)
+ | cls_key == genClassKey = Just (cond_RepresentableOk `andCond`
+ checkFlag Opt_DeriveGeneric)
+ | otherwise = Nothing
where
- ty_args_why = quotes (ppr (mkClassPred cls cls_tys)) <+> ptext SLIT("is not a class")
-
-non_std_why cls = quotes (ppr cls) <+> 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_mayDeriveDataTypeable `andCond` cond_typeableOK),
- (dataClassKey, cond_mayDeriveDataTypeable `andCond` cond_std)
- ]
-
-type Condition = (Bool, TyCon) -> Maybe SDoc
- -- Bool is whether or not we are allowed to derive Data and Typeable
+ cls_key = getUnique cls
+ cond_std = cond_stdOK mtheta
+
+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
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 -- c1 succeeds
+ Just x -> case c2 tc of -- c1 fails
Nothing -> Nothing
- Just y -> Just (x $$ ptext SLIT(" and") $$ y)
- -- Both fail
+ Just y -> Just (x $$ ptext (sLit " or") $$ y)
+ -- Both fail
+andCond :: Condition -> Condition -> Condition
andCond c1 c2 tc = case c1 tc of
Nothing -> c2 tc -- c1 succeeds
Just x -> Just x -- c1 fails
-cond_std :: Condition
-cond_std (_, rep_tc)
- | any (not . isVanillaDataCon) data_cons = Just existential_why
- | null data_cons = Just no_cons_why
- | otherwise = Nothing
+cond_stdOK :: DerivContext -> Condition
+cond_stdOK (Just _) _
+ = Nothing -- Don't check these conservative conditions for
+ -- standalone deriving; just generate the code
+ -- and let the typechecker handle the result
+cond_stdOK Nothing (_, rep_tc)
+ | null data_cons = Just (no_cons_why rep_tc $$ suggestion)
+ | not (null con_whys) = Just (vcat con_whys $$ suggestion)
+ | 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)")
+ suggestion = ptext (sLit "Possible fix: use a standalone deriving declaration instead")
+ data_cons = tyConDataCons rep_tc
+ 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 "must have a Haskell-98 type")))
+no_cons_why :: TyCon -> SDoc
+no_cons_why rep_tc = quotes (pprSourceTyCon rep_tc) <+>
+ ptext (sLit "must have at least one data constructor")
+
+cond_RepresentableOk :: Condition
+cond_RepresentableOk (_,t) = canDoGenerics t
+
+cond_enumOrProduct :: Condition
+cond_enumOrProduct = cond_isEnumeration `orCond`
+ (cond_isProduct `andCond` cond_noUnliftedArgs)
+
+cond_noUnliftedArgs :: Condition
+-- For some classes (eg Eq, Ord) we allow unlifted arg types
+-- by generating specilaised code. For others (eg Data) we don't.
+cond_noUnliftedArgs (_, tc)
+ | null bad_cons = Nothing
+ | otherwise = Just why
+ where
+ bad_cons = [ con | con <- tyConDataCons tc
+ , any isUnLiftedType (dataConOrigArgTys con) ]
+ why = badCon (head bad_cons) (ptext (sLit "must have only arguments of lifted type"))
+
cond_isEnumeration :: Condition
cond_isEnumeration (_, rep_tc)
- | isEnumerationTyCon rep_tc = Nothing
- | otherwise = Just why
+ | isEnumerationTyCon rep_tc = Nothing
+ | otherwise = Just why
where
- why = quotes (pprSourceTyCon rep_tc) <+>
- ptext SLIT("has non-nullary constructors")
+ why = sep [ quotes (pprSourceTyCon rep_tc) <+>
+ ptext (sLit "must be an enumeration type")
+ , ptext (sLit "(an enumeration consists of one or more nullary, non-GADT constructors)") ]
+ -- See Note [Enumeration types] in TyCon
cond_isProduct :: Condition
cond_isProduct (_, rep_tc)
| otherwise = Just why
where
why = quotes (pprSourceTyCon rep_tc) <+>
- ptext SLIT("has more than one constructor")
+ ptext (sLit "must have precisely one constructor")
cond_typeableOK :: Condition
-- OK for Typeable class
-- Currently: (a) args all of kind *
-- (b) 7 or fewer args
-cond_typeableOK (_, rep_tc)
- | tyConArity rep_tc > 7 = Just too_many
- | not (all (isSubArgTypeKind . tyVarKind) (tyConTyVars rep_tc))
- = Just bad_kind
- | isFamInstTyCon rep_tc = Just fam_inst -- no Typable for family insts
- | otherwise = Nothing
+cond_typeableOK (_, tc)
+ | tyConArity tc > 7 = Just too_many
+ | not (all (isSubArgTypeKind . tyVarKind) (tyConTyVars tc))
+ = Just bad_kind
+ | otherwise = Nothing
where
- too_many = quotes (pprSourceTyCon rep_tc) <+>
- ptext SLIT("has too many arguments")
- bad_kind = quotes (pprSourceTyCon rep_tc) <+>
- ptext SLIT("has arguments of kind other than `*'")
- fam_inst = quotes (pprSourceTyCon rep_tc) <+>
- ptext SLIT("is a type family")
-
-cond_mayDeriveDataTypeable :: Condition
-cond_mayDeriveDataTypeable (mayDeriveDataTypeable, _)
- | mayDeriveDataTypeable = Nothing
- | otherwise = Just why
- where
- why = ptext SLIT("You need -fglasgow-exts to derive an instance for this class")
+ too_many = quotes (pprSourceTyCon tc) <+>
+ ptext (sLit "must have 7 or fewer arguments")
+ bad_kind = quotes (pprSourceTyCon tc) <+>
+ ptext (sLit "must only have arguments of kind `*'")
+
+functorLikeClassKeys :: [Unique]
+functorLikeClassKeys = [functorClassKey, foldableClassKey, traversableClassKey]
+
+cond_functorOK :: Bool -> Condition
+-- OK for Functor/Foldable/Traversable 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
+-- (e) no "stupid context" on data type
+cond_functorOK allowFunctions (_, rep_tc)
+ | null tc_tvs
+ = Just (ptext (sLit "Data type") <+> quotes (ppr rep_tc)
+ <+> ptext (sLit "must have some type parameters"))
+
+ | not (null bad_stupid_theta)
+ = Just (ptext (sLit "Data type") <+> quotes (ppr rep_tc)
+ <+> ptext (sLit "must not have a class context") <+> pprTheta bad_stupid_theta)
-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]
+ | otherwise
+ = msum (map check_con data_cons) -- msum picks the first 'Just', if any
+ where
+ tc_tvs = tyConTyVars rep_tc
+ Just (_, last_tv) = snocView tc_tvs
+ bad_stupid_theta = filter is_bad (tyConStupidTheta rep_tc)
+ is_bad pred = last_tv `elemVarSet` tyVarsOfPred pred
+
+ 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 "must not have existential arguments")
+ covariant = ptext (sLit "must not use the type variable in a function argument")
+ functions = ptext (sLit "must not contain function types")
+ wrong_arg = ptext (sLit "must not use the type variable in an argument other than the last")
+
+checkFlag :: ExtensionFlag -> Condition
+checkFlag flag (dflags, _)
+ | xopt flag dflags = Nothing
+ | otherwise = Just why
+ where
+ why = ptext (sLit "You need -X") <> text flag_str
+ <+> ptext (sLit "to derive an instance for this class")
+ flag_str = case [ s | (s, f, _) <- xFlags, f==flag ] of
+ [s] -> s
+ other -> pprPanic "checkFlag" (ppr other)
+
+std_class_via_iso :: Class -> Bool
+-- These standard classes can be derived for a newtype
+-- using the isomorphism trick *even if no -XGeneralizedNewtypeDeriving
+-- because giving so gives the same results as generating the boilerplate
+std_class_via_iso clas
+ = classKey clas `elem` [eqClassKey, ordClassKey, ixClassKey, boundedClassKey]
-- Not Read/Show because they respect the type
-- Not Enum, because newtypes are never in Enum
+non_iso_class :: Class -> Bool
+-- *Never* derive Read, Show, Typeable, Data, Generic by isomorphism,
+-- even with -XGeneralizedNewtypeDeriving
+non_iso_class cls
+ = classKey cls `elem` ([ readClassKey, showClassKey, dataClassKey
+ , genClassKey] ++ typeableClassKeys)
+
+typeableClassKeys :: [Unique]
+typeableClassKeys = map getUnique typeableClassNames
+
+new_dfun_name :: Class -> TyCon -> TcM Name
new_dfun_name clas tycon -- Just a simple wrapper
- = newDFunName clas [mkTyConApp tycon []] (getSrcSpan tycon)
+ = do { loc <- getSrcSpanM -- The location of the instance decl, not of the tycon
+ ; 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]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+In general, a derived instance decl needs the superclasses of the derived
+class too. So if we have
+ data T a = ...deriving( Ord )
+then the initial context for Ord (T a) should include Eq (T a). Often this is
+redundant; we'll also generate an Ord constraint for each constructor argument,
+and that will probably generate enough constraints to make the Eq (T a) constraint
+be satisfied too. But not always; consider:
+
+ data S a = S
+ instance Eq (S a)
+ instance Ord (S a)
+
+ data T a = MkT (S a) deriving( Ord )
+ instance Num a => Eq (T a)
+
+The derived instance for (Ord (T a)) must have a (Num a) constraint!
+Similarly consider:
+ data T a = MkT deriving( Data, Typeable )
+Here there *is* no argument field, but we must nevertheless generate
+a context for the Data instances:
+ instance Typable a => Data (T a) where ...
+
%************************************************************************
%* *
%************************************************************************
\begin{code}
-mkNewTypeEqn :: InstOrigin -> Bool -> Bool -> OverlapFlag -> [Var] -> Class
+mkNewTypeEqn :: CtOrigin -> DynFlags -> [Var] -> Class
-> [Type] -> TyCon -> [Type] -> TyCon -> [Type]
- -> TcRn (Maybe DerivEqn, Maybe InstInfo)
-mkNewTypeEqn orig mayDeriveDataTypeable newtype_deriving overlap_flag tvs cls cls_tys
- tycon tc_args
- rep_tycon rep_tc_args
+ -> DerivContext
+ -> TcRn EarlyDerivSpec
+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)
- = 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
- | newtype_deriving = baleOut cant_derive_err -- Too hard
- | otherwise = baleOut std_err -- Just complain about being a non-std instance
+ = do { traceTc "newtype deriving:" (ppr tycon <+> ppr rep_tys <+> ppr all_preds)
+ ; dfun_name <- new_dfun_name cls tycon
+ ; 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_tc_args = rep_tc_args
+ , ds_theta = mtheta `orElse` all_preds
+ , ds_newtype = True }
+ ; return (if isJust mtheta then Right spec
+ else Left spec) }
+
+ | otherwise
+ = case checkSideConditions dflags mtheta cls cls_tys rep_tycon of
+ CanDerive -> go_for_it -- Use the standard H98 method
+ DerivableClassError msg -- Error with standard class
+ | can_derive_via_isomorphism -> bale_out (msg $$ suggest_nd)
+ | otherwise -> bale_out msg
+ NonDerivableClass -- Must use newtype deriving
+ | newtype_deriving -> bale_out cant_derive_err -- Too hard, even with newtype deriving
+ | can_derive_via_isomorphism -> bale_out (non_std $$ suggest_nd) -- Try newtype deriving!
+ | otherwise -> bale_out non_std
where
- mb_std_err = checkSideConditions mayDeriveDataTypeable cls cls_tys rep_tycon
- std_err = derivingThingErr cls cls_tys tc_app $
- vcat [fromJust mb_std_err,
- ptext SLIT("Try -XGeneralizedNewtypeDeriving for GHC's newtype-deriving extension")]
+ newtype_deriving = xopt Opt_GeneralizedNewtypeDeriving dflags
+ go_for_it = mk_data_eqn orig tvs cls tycon tc_args rep_tycon rep_tc_args mtheta
+ bale_out msg = failWithTc (derivingThingErr newtype_deriving cls cls_tys inst_ty msg)
+
+ non_std = nonStdErr cls
+ suggest_nd = ptext (sLit "Try -XGeneralizedNewtypeDeriving 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, ...)
-- with the last parameter missing
-- (T a1 .. ak) matches the kind of C's last argument
-- (and hence so does t)
+ -- The latter kind-check has been done by deriveTyData already,
+ -- and tc_args are already trimmed
--
-- We generate the instance
-- instance forall ({a1..ak} u fvs(s1..sm)).
-- We generate the instance
-- instance Monad (ST s) => Monad (T s) where
- cls_tyvars = classTyVars cls
- kind = tyVarKind (last cls_tyvars)
- -- Kind of the thing we want to instance
- -- e.g. argument kind of Monad, *->*
-
- (arg_kinds, _) = splitKindFunTys kind
- n_args_to_drop = length arg_kinds
- -- Want to drop 1 arg from (T s a) and (ST s a)
- -- to get instance Monad (ST s) => Monad (T s)
-
- -- Note [newtype representation]
- -- Need newTyConRhs *not* newTyConRep to get the representation
- -- type, because the latter looks through all intermediate newtypes
- -- For example
+ 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 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
+
+ -- Note [Newtype representation]
+ -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ -- Need newTyConRhs (*not* a recursive representation finder)
+ -- to get the representation type. For example
-- newtype B = MkB Int
-- 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!
- rep_ty = newTyConInstRhs rep_tycon rep_tc_args
- (rep_fn, rep_ty_args) = tcSplitAppTys rep_ty
-
- 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
-
- rep_fn' = mkAppTys rep_fn args_to_keep
- rep_tys = cls_tys ++ [rep_fn']
- rep_pred = mkClassPred cls rep_tys
+ rep_inst_ty = newTyConInstRhs rep_tycon rep_tc_args
+ rep_tys = cls_tys ++ [rep_inst_ty]
+ 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
- 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
- inst_tys = cls_tys ++ [tc_app]
+ cls_tyvars = classTyVars cls
+ dfun_tvs = tyVarsOfTypes inst_tys
+ inst_ty = mkTyConApp tycon tc_args
+ inst_tys = cls_tys ++ [inst_ty]
sc_theta = substTheta (zipOpenTvSubst cls_tyvars inst_tys)
(classSCTheta cls)
-- instance C T
-- rather than
-- instance C Int => C T
- 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 cls inst_tys
-------------------------------------------------------------------
-- Figuring out whether we can only do this newtype-deriving thing
- 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 cls `elem` non_iso_classes)
- && right_arity -- Well kinded;
- -- eg not: newtype T ... deriving( ST )
- -- because ST needs *2* type params
- && 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 )
- && 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
+ = not (non_iso_class cls)
+ && arity_ok
+ && eta_ok
+ && ats_ok
+-- && not (isRecursiveTyCon tycon) -- Note [Recursive newtypes]
+
+ 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 = (args_to_drop `tcEqTypes` dropped_tc_args)
- -- (a) the dropped-off args are identical in the source and rep type
+ eta_ok = nt_eta_arity <= length rep_tc_args
+ -- The newtype can be eta-reduced to match the number
+ -- of type argument actually supplied
-- 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)
- -- (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
-
- && 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 cls cls_tys tc_app
- (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 (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 if not eta_ok then
- ptext SLIT("the eta-reduction property does not hold")
- else empty
- ])
+ -- And the [a] must not mention 'b'. That's all handled
+ -- by nt_eta_rity.
+
+ 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 [ ppUnless arity_ok arity_msg
+ , ppUnless eta_ok eta_msg
+ , ppUnless ats_ok 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.
+
%************************************************************************
%* *
\end{itemize}
\begin{code}
-solveDerivEqns :: OverlapFlag
- -> [DerivEqn]
- -> TcM [Instance]-- Solns in same order as eqns.
- -- This bunch is Absolutely minimal...
-
-solveDerivEqns overlap_flag orig_eqns
- = do { traceTc (text "solveDerivEqns" <+> vcat (map pprDerivEqn orig_eqns))
- ; iterateDeriv 1 initial_solutions }
+inferInstanceContexts :: OverlapFlag -> [DerivSpec] -> TcM [DerivSpec]
+
+inferInstanceContexts _ [] = return []
+
+inferInstanceContexts oflag infer_specs
+ = do { traceTc "inferInstanceContexts" $ vcat (map pprDerivSpec infer_specs)
+ ; iterate_deriv 1 initial_solutions }
where
+ ------------------------------------------------------------------
-- The initial solutions for the equations claim that each
-- instance has an empty context; this solution is certainly
-- in canonical form.
- initial_solutions :: [DerivSoln]
- initial_solutions = [ [] | _ <- orig_eqns ]
+ initial_solutions :: [ThetaType]
+ initial_solutions = [ [] | _ <- infer_specs ]
------------------------------------------------------------------
- -- iterateDeriv calculates the next batch of solutions,
+ -- iterate_deriv calculates the next batch of solutions,
-- compares it with the current one; finishes if they are the
-- same, otherwise recurses with the new solutions.
-- It fails if any iteration fails
- iterateDeriv :: Int -> [DerivSoln] -> TcM [Instance]
- iterateDeriv n current_solns
+ iterate_deriv :: Int -> [ThetaType] -> TcM [DerivSpec]
+ iterate_deriv n current_solns
| n > 20 -- Looks as if we are in an infinite loop
- -- This can happen if we have -fallow-undecidable-instances
+ -- This can happen if we have -XUndecidableInstances
-- (See TcSimplify.tcSimplifyDeriv.)
= pprPanic "solveDerivEqns: probable loop"
- (vcat (map pprDerivEqn orig_eqns) $$ ppr current_solns)
+ (vcat (map pprDerivSpec infer_specs) $$ ppr current_solns)
| otherwise
- = let
- inst_specs = zipWithEqual "add_solns" mk_inst_spec
- orig_eqns current_solns
- in
- checkNoErrs (
- -- Extend the inst info from the explicit instance decls
+ = do { -- Extend the inst info from the explicit instance decls
-- with the current set of solutions, and simplify each RHS
- extendLocalInstEnv inst_specs $
- mappM gen_soln orig_eqns
- ) `thenM` \ new_solns ->
- if (current_solns == new_solns) then
- returnM inst_specs
- else
- iterateDeriv (n+1) new_solns
+ let inst_specs = zipWithEqual "add_solns" (mkInstance oflag)
+ current_solns infer_specs
+ ; new_solns <- checkNoErrs $
+ extendLocalInstEnv inst_specs $
+ mapM gen_soln infer_specs
+
+ ; if (current_solns == new_solns) then
+ return [ spec { ds_theta = soln }
+ | (spec, soln) <- zip infer_specs current_solns ]
+ else
+ iterate_deriv (n+1) new_solns }
------------------------------------------------------------------
- gen_soln :: DerivEqn -> TcM [PredType]
- gen_soln (loc, orig, _, tyvars, clas, inst_ty, deriv_rhs)
+ gen_soln :: DerivSpec -> TcM [PredType]
+ gen_soln (DS { ds_loc = loc, ds_orig = orig, ds_tvs = tyvars
+ , ds_cls = clas, ds_tys = inst_tys, ds_theta = deriv_rhs })
= setSrcSpan loc $
- addErrCtxt (derivInstCtxt clas [inst_ty]) $
- do { theta <- tcSimplifyDeriv orig tyvars deriv_rhs
- -- 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
+ addErrCtxt (derivInstCtxt the_pred) $
+ do { -- 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.
+ -- equality when finding the fixpoint. Moreover, simplifyDeriv
+ -- has an assert failure because it finds a TyVar when it expects
+ -- only TcTyVars. So I just rule it out for now. I'm not
+ -- even sure how it can arise.
+
; let tv_set = mkVarSet tyvars
- weird_preds = [pred | pred <- theta, not (tyVarsOfPred pred `subVarSet` tv_set)]
+ weird_preds = [pred | pred <- deriv_rhs
+ , not (tyVarsOfPred pred `subVarSet` tv_set)]
; mapM_ (addErrTc . badDerivedPred) weird_preds
+ ; theta <- simplifyDeriv orig the_pred tyvars deriv_rhs
+ -- checkValidInstance tyvars theta clas inst_tys
+ -- Not necessary; see Note [Exotic derived instance contexts]
+ -- in TcSimplify
+
+ ; traceTc "TcDeriv" (ppr deriv_rhs $$ ppr theta)
-- 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
+ the_pred = mkClassPred clas inst_tys
+
+------------------------------------------------------------------
+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
+ where
+ dfun = mkDictFunId dfun_name tyvars theta clas tys
- ------------------------------------------------------------------
- mk_inst_spec :: DerivEqn -> DerivSoln -> Instance
- mk_inst_spec (loc, orig, dfun_name, tyvars, clas, inst_ty, _) theta
- = mkLocalInstance dfun overlap_flag
- where
- 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
-- Representation tycons differ from the tycon in the instance signature in
-- case of instances for indexed families.
--
-genInst :: Instance -> TcM ((InstInfo, TyCon), LHsBinds RdrName)
-genInst spec
- = do { fix_env <- getFixityEnv
- ; let
- (tyvars,_,clas,[ty]) = instanceHead spec
- clas_nm = className clas
- (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, _) <- tcLookupFamInstExact visible_tycon tyArgs
- ; let (meth_binds, aux_binds) = genDerivBinds clas fix_env tycon
-
- -- Bring the right type variables into
- -- scope, and rename the method binds
- -- It's a bit yukky that we return *renamed* InstInfo, but
- -- *non-renamed* auxiliary bindings
- ; (rn_meth_binds, _fvs) <- discardWarnings $
- bindLocalNames (map Var.varName tyvars) $
- rnMethodBinds clas_nm (\n -> []) [] meth_binds
-
- -- Build the InstInfo
- ; return ((InstInfo { iSpec = spec,
- iBinds = VanillaInst rn_meth_binds [] }, tycon),
- aux_binds)
- }
-
-genDerivBinds clas fix_env tycon
+genInst :: Bool -- True <=> standalone deriving
+ -> OverlapFlag
+ -> DerivSpec -> TcM (InstInfo RdrName, DerivAuxBinds)
+genInst standalone_deriv oflag
+ spec@(DS { ds_tc = rep_tycon, ds_tc_args = rep_tc_args
+ , ds_theta = theta, ds_newtype = is_newtype
+ , ds_name = name, ds_cls = clas })
+ | is_newtype
+ = return (InstInfo { iSpec = inst_spec
+ , iBinds = NewTypeDerived co rep_tycon }, [])
+
+ | otherwise
+ = do { fix_env <- getFixityEnv
+ ; let loc = getSrcSpan name
+ (meth_binds, aux_binds) = genDerivBinds loc fix_env clas rep_tycon
+ -- In case of a family instance, we need to use the representation
+ -- tycon (after all, it has the data constructors)
+
+ ; return (InstInfo { iSpec = inst_spec
+ , iBinds = VanillaInst meth_binds [] standalone_deriv }
+ , aux_binds) }
+ where
+ inst_spec = mkInstance oflag theta spec
+ co1 = case tyConFamilyCoercion_maybe rep_tycon of
+ Just co_con -> mkAxInstCo co_con rep_tc_args
+ Nothing -> id_co
+ -- Not a family => rep_tycon = main tycon
+ co2 = mkAxInstCo (newTyConCo rep_tycon) rep_tc_args
+ co = co1 `mkTransCo` co2
+ id_co = mkReflCo (mkTyConApp rep_tycon rep_tc_args)
+
+-- 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)
+-- co : N [(b,b)] ~ Tree (b,b)
+
+genDerivBinds :: SrcSpan -> FixityEnv -> Class -> TyCon -> (LHsBinds RdrName, DerivAuxBinds)
+genDerivBinds loc fix_env clas tycon
| className clas `elem` typeableClassNames
- = (gen_Typeable_binds tycon, emptyLHsBinds)
+ = (gen_Typeable_binds loc tycon, [])
| otherwise
= case assocMaybe gen_list (getUnique clas) of
- Just gen_fn -> gen_fn fix_env tycon
+ Just gen_fn -> gen_fn loc tycon
Nothing -> pprPanic "genDerivBinds: bad derived class" (ppr clas)
where
- gen_list :: [(Unique, FixityEnv -> TyCon -> (LHsBinds RdrName, LHsBinds RdrName))]
- gen_list = [(eqClassKey, no_aux_binds (ignore_fix_env gen_Eq_binds))
- ,(ordClassKey, no_aux_binds (ignore_fix_env gen_Ord_binds))
- ,(enumClassKey, no_aux_binds (ignore_fix_env gen_Enum_binds))
- ,(boundedClassKey, no_aux_binds (ignore_fix_env gen_Bounded_binds))
- ,(ixClassKey, no_aux_binds (ignore_fix_env gen_Ix_binds))
- ,(typeableClassKey,no_aux_binds (ignore_fix_env gen_Typeable_binds))
- ,(showClassKey, no_aux_binds gen_Show_binds)
- ,(readClassKey, no_aux_binds gen_Read_binds)
- ,(dataClassKey, gen_Data_binds)
+ gen_list :: [(Unique, SrcSpan -> TyCon -> (LHsBinds RdrName, DerivAuxBinds))]
+ gen_list = [(eqClassKey, gen_Eq_binds)
+ ,(ordClassKey, gen_Ord_binds)
+ ,(enumClassKey, gen_Enum_binds)
+ ,(boundedClassKey, gen_Bounded_binds)
+ ,(ixClassKey, gen_Ix_binds)
+ ,(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)
+ ,(genClassKey, genGenericBinds)
]
-
- -- no_aux_binds is used for generators that don't
- -- need to produce any auxiliary bindings
- no_aux_binds f fix_env tc = (f fix_env tc, emptyLHsBinds)
- ignore_fix_env f fix_env tc = f tc
\end{code}
-
%************************************************************************
%* *
-\subsection[TcDeriv-taggery-Names]{What con2tag/tag2con functions are available?}
+\subsection[TcDeriv-generic-binds]{Bindings for the new generic deriving mechanism}
%* *
%************************************************************************
-
-data Foo ... = ...
-
-con2tag_Foo :: Foo ... -> Int#
-tag2con_Foo :: Int -> Foo ... -- easier if Int, not Int#
-maxtag_Foo :: Int -- ditto (NB: not unlifted)
-
-
-We have a @con2tag@ function for a tycon if:
+For the generic representation we need to generate:
\begin{itemize}
-\item
-We're deriving @Eq@ and the tycon has nullary data constructors.
-
-\item
-Or: we're deriving @Ord@ (unless single-constructor), @Enum@, @Ix@
-(enum type only????)
+\item A Generic instance
+\item A Rep type instance
+\item Many auxiliary datatypes and instances for them (for the meta-information)
\end{itemize}
-We have a @tag2con@ function for a tycon if:
-\begin{itemize}
-\item
-We're deriving @Enum@, or @Ix@ (enum type only???)
-\end{itemize}
-
-If we have a @tag2con@ function, we also generate a @maxtag@ constant.
+@genGenericBinds@ does (1)
+@genGenericRepExtras@ does (2) and (3)
+@genGenericAll@ does all of them
\begin{code}
-genTaggeryBinds :: [(InstInfo, TyCon)] -> TcM (LHsBinds RdrName)
-genTaggeryBinds infos
- = do { names_so_far <- foldlM do_con2tag [] tycons_of_interest
- ; nm_alist_etc <- foldlM do_tag2con names_so_far tycons_of_interest
- ; return (listToBag (map gen_tag_n_con_monobind nm_alist_etc)) }
- where
- all_CTs = [ (fst (simpleInstInfoClsTy info), tc)
- | (info, tc) <- infos]
- all_tycons = map snd all_CTs
- (tycons_of_interest, _) = removeDups compare all_tycons
-
- do_con2tag acc_Names tycon
- | isDataTyCon tycon &&
- ((we_are_deriving eqClassKey tycon
- && any isNullarySrcDataCon (tyConDataCons tycon))
- || (we_are_deriving ordClassKey tycon
- && not (isProductTyCon tycon))
- || (we_are_deriving enumClassKey tycon)
- || (we_are_deriving ixClassKey tycon))
-
- = returnM ((con2tag_RDR tycon, tycon, GenCon2Tag)
- : acc_Names)
- | otherwise
- = returnM acc_Names
-
- do_tag2con acc_Names tycon
- | isDataTyCon tycon &&
- (we_are_deriving enumClassKey tycon ||
- we_are_deriving ixClassKey tycon
- && isEnumerationTyCon tycon)
- = returnM ( (tag2con_RDR tycon, tycon, GenTag2Con)
- : (maxtag_RDR tycon, tycon, GenMaxTag)
- : acc_Names)
- | otherwise
- = returnM acc_Names
-
- we_are_deriving clas_key tycon
- = is_in_eqns clas_key tycon all_CTs
- where
- is_in_eqns clas_key tycon [] = False
- is_in_eqns clas_key tycon ((c,t):cts)
- = (clas_key == classKey c && tycon == t)
- || is_in_eqns clas_key tycon cts
+genGenericBinds :: SrcSpan -> TyCon -> (LHsBinds RdrName, DerivAuxBinds)
+genGenericBinds _ tc = (mkBindsRep tc, [ {- No DerivAuxBinds -} ])
+
+genGenericRepExtras :: TyCon -> TcM (MetaTyCons, TyCon)
+genGenericRepExtras tc =
+ do uniqS <- newUniqueSupply
+ let
+ -- Uniques for everyone
+ (uniqD:uniqs) = uniqsFromSupply uniqS
+ (uniqsC,us) = splitAt (length tc_cons) uniqs
+ uniqsS :: [[Unique]] -- Unique supply for the S datatypes
+ uniqsS = mkUniqsS tc_arits us
+ mkUniqsS [] _ = []
+ mkUniqsS (n:t) us = case splitAt n us of
+ (us1,us2) -> us1 : mkUniqsS t us2
+
+ tc_name = tyConName tc
+ tc_cons = tyConDataCons tc
+ tc_arits = map dataConSourceArity tc_cons
+
+ tc_occ = nameOccName tc_name
+ d_occ = mkGenD tc_occ
+ c_occ m = mkGenC tc_occ m
+ s_occ m n = mkGenS tc_occ m n
+ mod_name = nameModule (tyConName tc)
+ d_name = mkExternalName uniqD mod_name d_occ wiredInSrcSpan
+ c_names = [ mkExternalName u mod_name (c_occ m) wiredInSrcSpan
+ | (u,m) <- zip uniqsC [0..] ]
+ s_names = [ [ mkExternalName u mod_name (s_occ m n) wiredInSrcSpan
+ | (u,n) <- zip us [0..] ] | (us,m) <- zip uniqsS [0..] ]
+
+ mkTyCon name = ASSERT( isExternalName name )
+ buildAlgTyCon name [] [] mkAbstractTyConRhs
+ NonRecursive False NoParentTyCon Nothing
+
+ metaDTyCon <- mkTyCon d_name
+ metaCTyCons <- sequence [ mkTyCon c_name | c_name <- c_names ]
+ metaSTyCons <- mapM sequence
+ [ [ mkTyCon s_name
+ | s_name <- s_namesC ] | s_namesC <- s_names ]
+
+ let metaDts = MetaTyCons metaDTyCon metaCTyCons metaSTyCons
+
+ rep0_tycon <- tc_mkRepTyCon tc metaDts
+
+ -- pprTrace "rep0" (ppr rep0_tycon) $
+ return (metaDts, rep0_tycon)
+{-
+genGenericAll :: TyCon
+ -> TcM ((InstInfo RdrName, DerivAuxBinds), MetaTyCons, TyCon)
+genGenericAll tc =
+ do (metaDts, rep0_tycon) <- genGenericRepExtras tc
+ clas <- tcLookupClass genClassName
+ dfun_name <- new_dfun_name clas tc
+ let
+ mkInstRep = (InstInfo { iSpec = inst, iBinds = binds }
+ , [ {- No DerivAuxBinds -} ])
+ inst = mkLocalInstance dfun NoOverlap
+ binds = VanillaInst (mkBindsRep tc) [] False
+
+ tvs = tyConTyVars tc
+ tc_ty = mkTyConApp tc (mkTyVarTys tvs)
+
+ dfun = mkDictFunId dfun_name (tyConTyVars tc) [] clas [tc_ty]
+ return (mkInstRep, metaDts, rep0_tycon)
+-}
+genDtMeta :: (TyCon, MetaTyCons) -> TcM [(InstInfo RdrName, DerivAuxBinds)]
+genDtMeta (tc,metaDts) =
+ do dClas <- tcLookupClass datatypeClassName
+ d_dfun_name <- new_dfun_name dClas tc
+ cClas <- tcLookupClass constructorClassName
+ c_dfun_names <- sequence [ new_dfun_name cClas tc | _ <- metaC metaDts ]
+ sClas <- tcLookupClass selectorClassName
+ s_dfun_names <- sequence (map sequence [ [ new_dfun_name sClas tc
+ | _ <- x ]
+ | x <- metaS metaDts ])
+ fix_env <- getFixityEnv
+
+ let
+ (dBinds,cBinds,sBinds) = mkBindsMetaD fix_env tc
+
+ -- Datatype
+ d_metaTycon = metaD metaDts
+ d_inst = mkLocalInstance d_dfun NoOverlap
+ d_binds = VanillaInst dBinds [] False
+ d_dfun = mkDictFunId d_dfun_name (tyConTyVars tc) [] dClas
+ [ mkTyConTy d_metaTycon ]
+ d_mkInst = (InstInfo { iSpec = d_inst, iBinds = d_binds }, [])
+
+ -- Constructor
+ c_metaTycons = metaC metaDts
+ c_insts = [ mkLocalInstance (c_dfun c ds) NoOverlap
+ | (c, ds) <- myZip1 c_metaTycons c_dfun_names ]
+ c_binds = [ VanillaInst c [] False | c <- cBinds ]
+ c_dfun c dfun_name = mkDictFunId dfun_name (tyConTyVars tc) [] cClas
+ [ mkTyConTy c ]
+ c_mkInst = [ (InstInfo { iSpec = is, iBinds = bs }, [])
+ | (is,bs) <- myZip1 c_insts c_binds ]
+
+ -- Selector
+ s_metaTycons = metaS metaDts
+ s_insts = map (map (\(s,ds) -> mkLocalInstance (s_dfun s ds) NoOverlap))
+ (myZip2 s_metaTycons s_dfun_names)
+ s_binds = [ [ VanillaInst s [] False | s <- ss ] | ss <- sBinds ]
+ s_dfun s dfun_name = mkDictFunId dfun_name (tyConTyVars tc) [] sClas
+ [ mkTyConTy s ]
+ s_mkInst = map (map (\(is,bs) -> (InstInfo {iSpec=is, iBinds=bs}, [])))
+ (myZip2 s_insts s_binds)
+
+ myZip1 :: [a] -> [b] -> [(a,b)]
+ myZip1 l1 l2 = ASSERT (length l1 == length l2) zip l1 l2
+
+ myZip2 :: [[a]] -> [[b]] -> [[(a,b)]]
+ myZip2 l1 l2 =
+ ASSERT (and (zipWith (>=) (map length l1) (map length l2)))
+ [ zip x1 x2 | (x1,x2) <- zip l1 l2 ]
+
+ return (d_mkInst : c_mkInst ++ concat s_mkInst)
\end{code}
+
+%************************************************************************
+%* *
+\subsection[TcDeriv-taggery-Names]{What con2tag/tag2con functions are available?}
+%* *
+%************************************************************************
+
\begin{code}
-derivingThingErr clas tys ty why
- = sep [hsep [ptext SLIT("Can't make a derived instance of"),
- quotes (ppr pred)],
- nest 2 (parens why)]
+derivingKindErr :: TyCon -> Class -> [Type] -> Kind -> Message
+derivingKindErr tc cls cls_tys cls_kind
+ = hang (ptext (sLit "Cannot derive well-kinded instance of form")
+ <+> quotes (pprClassPred cls cls_tys <+> parens (ppr tc <+> ptext (sLit "..."))))
+ 2 (ptext (sLit "Class") <+> quotes (ppr cls)
+ <+> ptext (sLit "expects an argument of kind") <+> quotes (pprKind cls_kind))
+
+derivingEtaErr :: Class -> [Type] -> Type -> Message
+derivingEtaErr cls cls_tys inst_ty
+ = sep [ptext (sLit "Cannot eta-reduce to an instance of form"),
+ nest 2 (ptext (sLit "instance (...) =>")
+ <+> pprClassPred cls (cls_tys ++ [inst_ty]))]
+
+typeFamilyPapErr :: TyCon -> Class -> [Type] -> Type -> Message
+typeFamilyPapErr tc cls cls_tys inst_ty
+ = hang (ptext (sLit "Derived instance") <+> quotes (pprClassPred cls (cls_tys ++ [inst_ty])))
+ 2 (ptext (sLit "requires illegal partial application of data type family") <+> ppr tc)
+
+derivingThingErr :: Bool -> Class -> [Type] -> Type -> Message -> Message
+derivingThingErr newtype_deriving clas tys ty why
+ = sep [(hang (ptext (sLit "Can't make a derived instance of"))
+ 2 (quotes (ppr pred))
+ $$ nest 2 extra) <> colon,
+ nest 2 why]
where
+ extra | newtype_deriving = ptext (sLit "(even with cunning newtype deriving)")
+ | otherwise = empty
pred = mkClassPred clas (tys ++ [ty])
+derivingHiddenErr :: TyCon -> SDoc
+derivingHiddenErr tc
+ = hang (ptext (sLit "The data constructors of") <+> quotes (ppr tc) <+> ptext (sLit "are not all in scope"))
+ 2 (ptext (sLit "so you cannot derive an instance for it"))
+
standaloneCtxt :: LHsType Name -> SDoc
-standaloneCtxt ty = ptext SLIT("In the stand-alone deriving instance for") <+> quotes (ppr ty)
+standaloneCtxt ty = hang (ptext (sLit "In the stand-alone deriving instance for"))
+ 2 (quotes (ppr ty))
-derivInstCtxt clas inst_tys
- = ptext SLIT("When deriving the instance for") <+> parens (pprClassPred clas inst_tys)
+derivInstCtxt :: PredType -> Message
+derivInstCtxt pred
+ = ptext (sLit "When deriving the instance for") <+> parens (ppr pred)
+badDerivedPred :: PredType -> Message
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)]
+ = 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}
-
-
projects / ghc-hetmet.git / blobdiff