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
import Class
import Type
+import Coercion
import ErrUtils
import MkId
import DataCon
import Util
import ListSetOps
import Outputable
+import FastString
import Bag
+
+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)
+\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 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
-\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.
%************************************************************************
%* *
%************************************************************************
\begin{code}
-tcDeriving :: [LTyClDecl Name] -- All type constructors
+tcDeriving :: [LTyClDecl Name] -- All type constructors
+ -> [LInstDecl Name] -- All instance declarations
-> [LDerivDecl Name] -- All stand-alone deriving declarations
- -> TcM ([InstInfo], -- The generated "instance decls"
- HsValBinds Name) -- Extra generated top-level bindings
+ -> TcM ([InstInfo Name], -- The generated "instance decls"
+ HsValBinds Name, -- Extra generated top-level bindings
+ DefUses)
-tcDeriving tycl_decls deriv_decls
- = recoverM (returnM ([], emptyValBindsOut)) $
+tcDeriving tycl_decls inst_decls deriv_decls
+ = recoverM (return ([], emptyValBindsOut, emptyDUs)) $
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_inst_info, deriv_binds)
- <- extendLocalInstEnv (map iSpec newtype_inst_info) $
- deriveOrdinaryStuff overlap_flag 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
- -- Set -fglasgow exts so that we can have type signatures in patterns,
- -- which is used in the generic binds
- ; rn_binds
- <- discardWarnings $ setOptM Opt_GlasgowExts $ 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 <- makeDerivSpecs is_boot tycl_decls inst_decls deriv_decls
+
+ ; 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
+
+ -- Generate the generic to/from functions from each type declaration
+ ; gen_binds <- mkGenericBinds is_boot tycl_decls
+ ; (inst_info, rn_binds, rn_dus) <- renameDeriv is_boot gen_binds (insts1 ++ insts2)
; 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))
- ; returnM (inst_info, rn_binds)
- }}
+ ; return (inst_info, rn_binds, rn_dus) }
where
- ddump_deriving :: [InstInfo] -> HsValBinds Name -> SDoc
+ ddump_deriving :: [InstInfo Name] -> HsValBinds Name -> SDoc
ddump_deriving inst_infos extra_binds
= vcat (map pprInstInfoDetails inst_infos) $$ ppr extra_binds
+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)) } }
+
+ where
+ (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 (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 (InstInfo { iSpec = inst, iBinds = binds' }, fvs) }
+ where
+ (tyvars,_, clas,_) = instanceHead inst
+ clas_nm = className clas
+
-----------------------------------------
-deriveOrdinaryStuff overlap_flag [] -- Short cut
- = returnM ([], emptyLHsBinds)
+mkGenericBinds :: Bool -> [LTyClDecl Name] -> TcM (LHsBinds RdrName)
+mkGenericBinds is_boot tycl_decls
+ | is_boot
+ = return emptyBag
+ | otherwise
+ = do { tcs <- mapM tcLookupTyCon [ tcdName d
+ | L _ d <- tycl_decls, isDataDecl d ]
+ ; return (unionManyBags [ mkTyConGenericBinds tc
+ | tc <- tcs, tyConHasGenerics tc ]) }
+ -- We are only interested in the data type declarations,
+ -- and then only in the ones whose 'has-generics' flag is on
+ -- The predicate tyConHasGenerics finds both of these
+\end{code}
-deriveOrdinaryStuff overlap_flag 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
+Note [Newtype deriving and unused constructors]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Consider this (see Trac #1954):
- -- Generate the InstInfo for each dfun,
- -- plus any auxiliary bindings it needs
- ; (inst_infos, aux_binds_s) <- mapAndUnzipM genInst inst_specs
+ module Bug(P) where
+ newtype P a = MkP (IO a) deriving Monad
- -- Generate any extra not-one-inst-decl-specific binds,
- -- notably "con2tag" and/or "tag2con" functions.
- ; extra_binds <- genTaggeryBinds inst_infos
+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...
- -- Done
- ; returnM (map fst inst_infos,
- unionManyBags (extra_binds : aux_binds_s))
- }
+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.
------------------------------------------
-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
+
+%************************************************************************
+%* *
+ From HsSyn to DerivSpec
+%* *
+%************************************************************************
+
+@makeDerivSpecs@ fishes around to find the info about needed derived instances.
+
+\begin{code}
+makeDerivSpecs :: Bool
+ -> [LTyClDecl Name]
+ -> [LInstDecl Name]
+ -> [LDerivDecl Name]
+ -> TcM [EarlyDerivSpec]
+
+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
+ ; return (eqns1 ++ eqns2) }
+ where
+ 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 EarlyDerivSpec
+-- Standalone deriving declarations
+-- 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 { traceTc "Standalone deriving decl for" (ppr deriv_ty)
+ ; (tvs, theta, tau) <- tcHsInstHead deriv_ty
+ ; traceTc "Standalone deriving;" $ vcat
+ [ text "tvs:" <+> ppr tvs
+ , text "theta:" <+> ppr theta
+ , text "tau:" <+> ppr tau ]
+ ; (cls, inst_tys) <- checkValidInstance deriv_ty tvs theta tau
+ -- 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 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]).
+
+ -- 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}
+
+Note [Deriving, type families, and partial applications]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+When there are no type families, it's quite easy:
+
+ newtype S a = MkS [a]
+ -- :CoS :: S ~ [] -- Eta-reduced
+
+ 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
+
+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
+
+ 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}
+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
+ = 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.
+ -- No need for this when deriving Typeable, becuase we don't need
+ -- the constructors for that.
+ ; 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))
+ ; checkTc (isNothing mtheta ||
+ not hidden_data_cons ||
+ className cls `elem` typeableClassNames)
+ (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 }
+ | otherwise
+ = failWithTc (derivingThingErr False cls cls_tys tc_app
+ (ptext (sLit "The last argument of the instance must be a data or newtype application")))
\end{code}
%************************************************************************
%* *
-\subsection[TcDeriv-eqns]{Forming the equations}
+ Deriving data types
%* *
%************************************************************************
-@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).
+\begin{code}
+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
+ 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)
-\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}
+mk_data_eqn, mk_typeable_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
+ | getName cls `elem` typeableClassNames
+ = mk_typeable_eqn orig tvs cls tycon tc_args rep_tc rep_tc_args mtheta
-[See Appendix~E in the Haskell~1.2 report.] This code here deals w/
-all those.
+ | otherwise
+ = 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 orig tvs cls tycon tc_args rep_tc rep_tc_args mtheta
+ -- 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
+ | 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 [] rep_tc [] (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 = rep_tc, ds_tc_args = rep_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
+ = 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
+ = []
-Note [Newtype deriving superclasses]
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-The 'tys' here come from the partial application in the deriving
-clause. The last arg is the new instance type.
+------------------------------------------------------------------
+-- Check side conditions that dis-allow derivability for particular classes
+-- This is *apart* from the newtype-deriving mechanism
+--
+-- Here we get the representation tycon in case of family instances as it has
+-- the data constructors - but we need to be careful to fall back to the
+-- family tycon (with indexes) in error messages.
+
+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")
+
+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)
+ | getName cls `elem` typeableClassNames = Just (checkFlag Opt_DeriveDataTypeable `andCond` cond_typeableOK)
+ | otherwise = Nothing
+ where
+ cls_key = getUnique cls
+ cond_std = cond_stdOK mtheta
-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
+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
+ Just y -> Just (x $$ ptext (sLit " and") $$ y)
+ -- Both fail
+andCond :: Condition -> Condition -> Condition
+andCond c1 c2 tc = case c1 tc of
+ Nothing -> c2 tc -- c1 succeeds
+ Just x -> Just x -- c1 fails
-\begin{code}
-type DerivSpec = (SrcSpan, -- location of the deriving clause
- InstOrigin, -- deriving at data decl or standalone?
- NewOrData, -- newtype or data type
- Name, -- Type constructor for which we derive
- [LHsTyVarBndr Name], -- Type variables
- Maybe [LHsType Name], -- Type indexes if indexed type
- LHsType Name) -- Class instance to be generated
-
-makeDerivEqns :: OverlapFlag
- -> [LTyClDecl Name]
- -> [LDerivDecl Name]
- -> TcM ([DerivEqn], -- Ordinary derivings
- [InstInfo]) -- Special newtype derivings
-
-makeDerivEqns overlap_flag tycl_decls deriv_decls
- = do derive_top_level <- mapM top_level_deriv deriv_decls
- (maybe_ordinaries, maybe_newtypes)
- <- mapAndUnzipM mk_eqn (derive_data ++ catMaybes derive_top_level)
- return (catMaybes maybe_ordinaries, catMaybes maybe_newtypes)
+cond_stdOK :: DerivContext -> Condition
+cond_stdOK (Just _) _
+ = Nothing -- Don't check these conservative conditions for
+ -- standalone deriving; just generate the code
+ -- and let the typechecker handle the result
+cond_stdOK Nothing (_, rep_tc)
+ | null data_cons = Just (no_cons_why rep_tc $$ suggestion)
+ | not (null con_whys) = Just (vcat con_whys $$ suggestion)
+ | otherwise = Nothing
where
- ------------------------------------------------------------------
- -- 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)
+ 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 "does not have a Haskell-98 type")))
+
+no_cons_why :: TyCon -> SDoc
+no_cons_why rep_tc = quotes (pprSourceTyCon rep_tc) <+>
+ ptext (sLit "has no data constructors")
+
+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 "has arguments of unlifted type"))
- ------------------------------------------------------------------
- -- 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
- }}
+cond_isEnumeration :: Condition
+cond_isEnumeration (_, rep_tc)
+ | isEnumerationTyCon rep_tc = Nothing
+ | otherwise = Just why
+ where
+ why = sep [ quotes (pprSourceTyCon rep_tc) <+>
+ ptext (sLit "is not an enumeration type")
+ , nest 2 $ ptext (sLit "(an enumeration consists of one or more nullary constructors)") ]
+ -- See Note [Enumeration types] in TyCon
- ------------------------------------------------------------------
- -- 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]
+cond_isProduct :: Condition
+cond_isProduct (_, rep_tc)
+ | isProductTyCon rep_tc = Nothing
+ | otherwise = Just why
+ where
+ why = quotes (pprSourceTyCon rep_tc) <+>
+ ptext (sLit "does not 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
+ 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")
+
+
+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 (dflags, rep_tc)
+ | not (xopt Opt_DeriveFunctor dflags)
+ = Just (ptext (sLit "You need -XDeriveFunctor to derive an instance for this class"))
+
+ | null tc_tvs
+ = Just (ptext (sLit "Data type") <+> quotes (ppr rep_tc)
+ <+> ptext (sLit "has no parameters"))
+
+ | not (null bad_stupid_theta)
+ = Just (ptext (sLit "Data type") <+> quotes (ppr rep_tc)
+ <+> ptext (sLit "has a class context") <+> pprTheta bad_stupid_theta)
+
+ | 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 "has existential arguments")
+ covariant = ptext (sLit "uses the type variable in a function argument")
+ functions = ptext (sLit "contains function types")
+ wrong_arg = ptext (sLit "uses 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 by isomorphism,
+-- even with -XGeneralizedNewtypeDeriving
+non_iso_class cls
+ = classKey cls `elem` ([readClassKey, showClassKey, dataClassKey] ++
+ typeableClassKeys)
+
+typeableClassKeys :: [Unique]
+typeableClassKeys = map getUnique typeableClassNames
+
+new_dfun_name :: Class -> TyCon -> TcM Name
+new_dfun_name clas tycon -- Just a simple wrapper
+ = 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 ...
+
+
+%************************************************************************
+%* *
+ Deriving newtypes
+%* *
+%************************************************************************
+
+\begin{code}
+mkNewTypeEqn :: CtOrigin -> DynFlags -> [Var] -> Class
+ -> [Type] -> TyCon -> [Type] -> TyCon -> [Type]
+ -> 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 "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
+ 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")
- 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
-
- 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)
- ; -- Go ahead and use the isomorphism
- dfun_name <- new_dfun_name clas 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
-- 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
-- (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
- clas_tyvars = classTyVars clas
- kind = tyVarKind (last clas_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!
- (tc_tvs, rep_ty) = newTyConRhs tycon
- (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_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 = tys ++ [rep_fn']
- rep_pred = mkClassPred clas 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
- -- 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)
- -- 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)
+ 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)
-- 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
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
-------------------------------------------------------------------
-- Figuring out whether we can only do this newtype-deriving thing
- right_arity = length tys + 1 == classArity clas
-
- -- 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)
- && 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:
- -- 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
-
- -- 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)
- && (tyVarsOfType rep_fn' `disjointVarSet` dropped_tvs)
- && (tyVarsOfTypes tys `disjointVarSet` dropped_tvs)
- && droppedIndexesAreVariables
-
- droppedIndexesAreVariables =
- case tyConFamInst_maybe tycon of
- Nothing -> True
- Just (famTyCon, tyIdxs) ->
- all isTyVarTy $ drop (tyConArity famTyCon - n_args_to_drop) tyIdxs
-
- cant_derive_err = derivingThingErr clas tys tycon (mkTyVarTys tyvars_to_keep)
- (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")
- else empty,
- if not (n_tyvars_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
- ])
-
- non_std_err = derivingThingErr clas tys tycon (mkTyVarTys tyvars_to_keep)
- (vcat [non_std_why clas,
- 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, [], []) }
+ = not (non_iso_class cls)
+ && arity_ok
+ && eta_ok
+ && ats_ok
+-- && not (isRecursiveTyCon tycon) -- Note [Recursive newtypes]
- | 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
+ arity_ok = length cls_tys + 1 == classArity cls
+ -- Well kinded; eg not: newtype T ... deriving( ST )
+ -- because ST needs *2* type params
- 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
+ -- Check that eta reduction is OK
+ 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)
+ -- 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}
-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")
+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.
-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")
+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.
-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}
%************************************************************************
%* *
\end{itemize}
\begin{code}
-solveDerivEqns :: OverlapFlag
- -> [DerivEqn]
- -> TcM [Instance]-- Solns in same order as eqns.
- -- This bunch is Absolutely minimal...
+inferInstanceContexts :: OverlapFlag -> [DerivSpec] -> TcM [DerivSpec]
+
+inferInstanceContexts _ [] = return []
-solveDerivEqns overlap_flag orig_eqns
- = iterateDeriv 1 initial_solutions
+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, _, clas, tc, tyvars, 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 $
- do { let inst_tys = [origHead]
- ; theta <- addErrCtxt (derivInstCtxt1 clas inst_tys) $
- tcSimplifyDeriv orig tc tyvars deriv_rhs
+ addErrCtxt (derivInstCtxt clas inst_tys) $
+ 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. 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 <- deriv_rhs
+ , not (tyVarsOfPred pred `subVarSet` tv_set)]
+ ; mapM_ (addErrTc . badDerivedPred) weird_preds
+
+ ; theta <- simplifyDeriv orig 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
- origHead = uncurry mkTyConApp (tyConOrigHead tc)
- ------------------------------------------------------------------
- mk_inst_spec :: DerivEqn -> DerivSoln -> Instance
- mk_inst_spec (loc, orig, dfun_name, clas, tycon, tyvars, _) theta
- = mkLocalInstance dfun overlap_flag
- where
- dfun = mkDictFunId dfun_name tyvars theta clas [origHead]
- origHead = uncurry mkTyConApp (tyConOrigHead tycon)
+------------------------------------------------------------------
+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
+
extendLocalInstEnv :: [Instance] -> TcM a -> TcM a
-- Add new locally-defined instances; don't bother to check
; setGblEnv env' thing_inside }
\end{code}
+
%************************************************************************
%* *
\subsection[TcDeriv-normal-binds]{Bindings for the various classes}
-- 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
+genInst :: Bool -- True <=> standalone deriving
+ -> OverlapFlag
+ -> DerivSpec -> TcM (InstInfo RdrName, DerivAuxBinds)
+genInst standalone_deriv oflag spec
+ | ds_newtype spec
+ = return (InstInfo { iSpec = mkInstance oflag (ds_theta spec) spec
+ , iBinds = NewTypeDerived co rep_tycon }, [])
+
+ | otherwise
+ = do { let loc = getSrcSpan (ds_name spec)
+ inst = mkInstance oflag (ds_theta spec) spec
+ clas = ds_cls spec
-- 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
- ; 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)
+ -- tycon (after all, it has the data constructors)
+ ; fix_env <- getFixityEnv
+ ; let (meth_binds, aux_binds) = genDerivBinds loc fix_env clas rep_tycon
+ binds = VanillaInst meth_binds [] standalone_deriv
+ ; return (InstInfo { iSpec = inst, iBinds = binds }, aux_binds)
}
-
-genDerivBinds clas fix_env tycon
+ where
+ rep_tycon = ds_tc spec
+ rep_tc_args = ds_tc_args spec
+ co1 = case tyConFamilyCoercion_maybe rep_tycon of
+ Just co_con -> ACo (mkTyConApp co_con rep_tc_args)
+ Nothing -> id_co
+ -- Not a family => rep_tycon = main tycon
+ co2 = case newTyConCo_maybe rep_tycon of
+ Just co_con -> ACo (mkTyConApp co_con rep_tc_args)
+ Nothing -> id_co -- The newtype is transparent; no need for a cast
+ co = co1 `mkTransCoI` co2
+ id_co = IdCo (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)
]
-
- -- 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}
%* *
%************************************************************************
-
-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:
-\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????)
-\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.
-
-\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
-\end{code}
-
\begin{code}
-derivingThingErr clas tys tycon ttys 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])
-
-derivCtxt :: Name -> Maybe [LHsType Name] -> SDoc
-derivCtxt tycon mb_tys
- = ptext SLIT("When deriving instances for") <+> quotes typeInst
+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
- 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)
+ 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 = hang (ptext (sLit "In the stand-alone deriving instance for"))
+ 2 (quotes (ppr ty))
+
+derivInstCtxt :: Class -> [Type] -> Message
+derivInstCtxt clas inst_tys
+ = ptext (sLit "When deriving the instance for") <+> parens (pprClassPred clas inst_tys)
+
+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)]
\end{code}
-
projects / ghc-hetmet.git / blobdiff