\section[TcClassDcl]{Typechecking class declarations}
\begin{code}
-module TcClassDcl ( tcClassDecl1, tcClassDecls2, mkImplicitClassBinds,
- tcMethodBind, checkFromThisClass
+module TcClassDcl ( tcClassSigs, tcClassDecl2,
+ getGenericInstances,
+ MethodSpec, tcMethodBind, mkMethodBind,
+ tcAddDeclCtxt, badMethodErr
) where
#include "HsVersions.h"
-import HsSyn ( HsDecl(..), TyClDecl(..), Sig(..), MonoBinds(..),
- HsExpr(..), HsLit(..), HsType(..), HsPred(..),
- mkSimpleMatch, andMonoBinds, andMonoBindList,
- isClassDecl, isClassOpSig, isPragSig, collectMonoBinders
+import HsSyn
+import RnHsSyn ( maybeGenericMatch, extractHsTyVars )
+import RnExpr ( rnLExpr )
+import RnEnv ( lookupTopBndrRn, lookupImportedName )
+import Inst ( instToId, newDicts, newDictsAtLoc, newMethod, getOverlapFlag )
+import InstEnv ( mkLocalInstance )
+import TcEnv ( tcLookupLocatedClass,
+ tcExtendTyVarEnv,
+ InstInfo(..), pprInstInfoDetails,
+ simpleInstInfoTyCon, simpleInstInfoTy,
+ InstBindings(..), newDFunName
)
-import BasicTypes ( TopLevelFlag(..), RecFlag(..) )
-import RnHsSyn ( RenamedTyClDecl,
- RenamedClassOpSig, RenamedMonoBinds,
- RenamedContext, RenamedHsDecl, RenamedSig
+import TcBinds ( TcPragFun, tcMonoBinds, tcPrags, mkPragFun )
+import TcHsType ( TcSigInfo(..), tcHsKindedType, tcHsSigType )
+import TcSimplify ( tcSimplifyCheck )
+import TcUnify ( checkSigTyVars, sigCtxt )
+import TcMType ( tcSkolSigTyVars, UserTypeCtxt( GenPatCtxt ), tcSkolType )
+import TcType ( Type, SkolemInfo(ClsSkol, InstSkol, SigSkol),
+ TcType, TcThetaType, TcTyVar, mkTyVarTys,
+ mkClassPred, tcSplitSigmaTy, tcSplitFunTys,
+ tcIsTyVarTy, tcSplitTyConApp_maybe, tcSplitForAllTys, tcSplitPhiTy,
+ getClassPredTys_maybe, mkPhiTy, mkTyVarTy
)
-import TcHsSyn ( TcMonoBinds, idsToMonoBinds )
-
-import Inst ( InstOrigin(..), LIE, emptyLIE, plusLIE, plusLIEs, newDicts, newMethod )
-import TcEnv ( TcId, ValueEnv, TyThing(..), TyThingDetails(..), tcAddImportedIdInfo,
- tcLookupTy, tcExtendTyVarEnvForMeths, tcExtendGlobalTyVars,
- tcExtendLocalValEnv, tcExtendTyVarEnv, newDefaultMethodName
- )
-import TcBinds ( tcBindWithSigs, tcSpecSigs )
-import TcMonoType ( tcHsSigType, tcClassContext, checkSigTyVars, sigCtxt, mkTcSig )
-import TcSimplify ( tcSimplifyAndCheck, bindInstsOfLocalFuns )
-import TcType ( TcType, TcTyVar, tcInstTyVars, zonkTcSigTyVars )
-import TcMonad
+import TcRnMonad
+import Generics ( mkGenericRhs, validGenericInstanceType )
import PrelInfo ( nO_METHOD_BINDING_ERROR_ID )
-import Bag ( bagToList )
-import Class ( classTyVars, classBigSig, classSelIds, classTyCon, Class, ClassOpItem )
-import CmdLineOpts ( opt_GlasgowExts, opt_WarnMissingMethods )
-import MkId ( mkDictSelId, mkDataConId, mkDataConWrapId, mkDefaultMethodId )
-import DataCon ( mkDataCon, notMarkedStrict )
-import Id ( Id, idType, idName )
-import Name ( Name, nameOccName, isLocallyDefined, NamedThing(..) )
-import NameSet ( NameSet, mkNameSet, elemNameSet, emptyNameSet )
+import Class ( classTyVars, classBigSig,
+ Class, ClassOpItem, DefMeth (..) )
+import TyCon ( TyCon, tyConName, tyConHasGenerics )
+import Type ( substTyWith )
+import MkId ( mkDefaultMethodId, mkDictFunId )
+import Id ( Id, idType, idName, mkUserLocal )
+import Name ( Name, NamedThing(..) )
+import NameEnv ( NameEnv, lookupNameEnv, mkNameEnv )
+import NameSet ( nameSetToList )
+import OccName ( reportIfUnused, mkDefaultMethodOcc )
+import RdrName ( RdrName, mkDerivedRdrName )
import Outputable
-import Type ( Type, ClassContext, mkTyVarTys, mkDictTys, mkSigmaTy, mkClassPred )
-import Var ( TyVar )
-import VarSet ( mkVarSet, emptyVarSet )
-import Maybes ( seqMaybe )
+import PrelNames ( genericTyConNames )
+import DynFlags
+import ErrUtils ( dumpIfSet_dyn )
+import Util ( count, lengthIs, isSingleton, lengthExceeds )
+import Unique ( Uniquable(..) )
+import ListSetOps ( equivClassesByUniq, minusList )
+import SrcLoc ( Located(..), srcSpanStart, unLoc, noLoc )
+import Maybes ( seqMaybe, isJust, mapCatMaybes )
+import List ( partition )
+import BasicTypes ( RecFlag(..) )
+import Bag
+import FastString
\end{code}
%************************************************************************
%* *
-\subsection{Type checking}
+ Type-checking the class op signatures
%* *
%************************************************************************
\begin{code}
-tcClassDecl1 :: ValueEnv -> RenamedTyClDecl -> TcM s (Name, TyThingDetails)
-tcClassDecl1 rec_env
- (ClassDecl context class_name
- tyvar_names fundeps class_sigs def_methods pragmas
- tycon_name datacon_name datacon_wkr_name sc_sel_names src_loc)
- = -- CHECK ARITY 1 FOR HASKELL 1.4
- checkTc (opt_GlasgowExts || length tyvar_names == 1)
- (classArityErr class_name) `thenTc_`
-
- -- LOOK THINGS UP IN THE ENVIRONMENT
- tcLookupTy class_name `thenTc` \ (AClass clas) ->
- let
- tyvars = classTyVars clas
- dm_bndrs_w_locs = bagToList (collectMonoBinders def_methods)
- dm_bndr_set = mkNameSet (map fst dm_bndrs_w_locs)
- in
- tcExtendTyVarEnv tyvars $
-
- -- CHECK THE CONTEXT
- tcSuperClasses class_name clas
- context sc_sel_names `thenTc` \ (sc_theta, sc_sel_ids) ->
-
- -- CHECK THE CLASS SIGNATURES,
- mapTc (tcClassSig rec_env dm_bndr_set clas tyvars)
- (filter isClassOpSig class_sigs) `thenTc` \ sig_stuff ->
-
- -- MAKE THE CLASS DETAILS
- let
- (op_tys, op_items) = unzip sig_stuff
- sc_tys = mkDictTys sc_theta
- dict_component_tys = sc_tys ++ op_tys
-
- dict_con = mkDataCon datacon_name
- [notMarkedStrict | _ <- dict_component_tys]
- [{- No labelled fields -}]
- tyvars
- [{-No context-}]
- [{-No existential tyvars-}] [{-Or context-}]
- dict_component_tys
- (classTyCon clas)
- dict_con_id dict_wrap_id
-
- dict_con_id = mkDataConId datacon_wkr_name dict_con
- dict_wrap_id = mkDataConWrapId dict_con
- in
- returnTc (class_name, ClassDetails sc_theta sc_sel_ids op_items dict_con)
-\end{code}
-
-\begin{code}
-tcSuperClasses :: Name -> Class
- -> RenamedContext -- class context
- -> [Name] -- Names for superclass selectors
- -> TcM s (ClassContext, -- the superclass context
- [Id]) -- superclass selector Ids
-
-tcSuperClasses class_name clas context sc_sel_names
- = -- Check the context.
- -- The renamer has already checked that the context mentions
- -- only the type variable of the class decl.
-
- -- For std Haskell check that the context constrains only tyvars
- (if opt_GlasgowExts then
- returnTc ()
- else
- mapTc_ check_constraint context
- ) `thenTc_`
-
- -- Context is already kind-checked
- tcClassContext context `thenTc` \ sc_theta ->
- let
- sc_sel_ids = [mkDictSelId sc_name clas | sc_name <- sc_sel_names]
- in
- -- Done
- returnTc (sc_theta, sc_sel_ids)
-
+tcClassSigs :: Name -- Name of the class
+ -> [LSig Name]
+ -> LHsBinds Name
+ -> TcM [TcMethInfo]
+
+type TcMethInfo = (Name, DefMeth, Type) -- A temporary intermediate, to communicate
+ -- between tcClassSigs and buildClass
+tcClassSigs clas sigs def_methods
+ = do { dm_env <- checkDefaultBinds clas op_names def_methods
+ ; mappM (tcClassSig dm_env) op_sigs }
where
- check_constraint sc@(HsPClass c tys)
- = checkTc (all is_tyvar tys) (superClassErr class_name sc)
-
- is_tyvar (HsTyVar _) = True
- is_tyvar other = False
-
+ op_sigs = [sig | sig@(L _ (TypeSig _ _)) <- sigs]
+ op_names = [n | sig@(L _ (TypeSig (L _ n) _)) <- op_sigs]
-tcClassSig :: ValueEnv -- Knot tying only!
- -> NameSet -- Names bound in the default-method bindings
- -> Class -- ...ditto...
- -> [TyVar] -- The class type variable, used for error check only
- -> RenamedClassOpSig
- -> TcM s (Type, -- Type of the method
- ClassOpItem) -- Selector Id, default-method Id, True if explicit default binding
+checkDefaultBinds :: Name -> [Name] -> LHsBinds Name -> TcM (NameEnv Bool)
+ -- Check default bindings
+ -- a) must be for a class op for this class
+ -- b) must be all generic or all non-generic
+ -- and return a mapping from class-op to Bool
+ -- where True <=> it's a generic default method
+checkDefaultBinds clas ops binds
+ = do dm_infos <- mapM (addLocM (checkDefaultBind clas ops)) (bagToList binds)
+ return (mkNameEnv dm_infos)
-tcClassSig rec_env dm_bind_names clas clas_tyvars
- (ClassOpSig op_name maybe_dm_stuff op_ty src_loc)
- = tcAddSrcLoc src_loc $
+checkDefaultBind clas ops (FunBind (L _ op) _ (MatchGroup matches _) _)
+ = do { -- Check that the op is from this class
+ checkTc (op `elem` ops) (badMethodErr clas op)
- -- Check the type signature. NB that the envt *already has*
- -- bindings for the type variables; see comments in TcTyAndClassDcls.
+ -- Check that all the defns ar generic, or none are
+ ; checkTc (all_generic || none_generic) (mixedGenericErr op)
- -- NB: Renamer checks that the class type variable is mentioned in local_ty,
- -- and that it is not constrained by theta
- tcHsSigType op_ty `thenTc` \ local_ty ->
- let
- global_ty = mkSigmaTy clas_tyvars
- [mkClassPred clas (mkTyVarTys clas_tyvars)]
- local_ty
-
- -- Build the selector id and default method id
- sel_id = mkDictSelId op_name clas
- in
- (case maybe_dm_stuff of
- Nothing -> -- Source-file class declaration
- newDefaultMethodName op_name src_loc `thenNF_Tc` \ dm_name ->
- returnNF_Tc (mkDefaultMethodId dm_name clas global_ty, op_name `elemNameSet` dm_bind_names)
-
- Just (dm_name, explicit_dm) -> -- Interface-file class decl
- let
- dm_id = mkDefaultMethodId dm_name clas global_ty
- in
- returnNF_Tc (tcAddImportedIdInfo rec_env dm_id, explicit_dm)
- ) `thenNF_Tc` \ (dm_id, explicit_dm) ->
-
- returnTc (local_ty, (sel_id, dm_id, explicit_dm))
-\end{code}
-
-
-%************************************************************************
-%* *
-\subsection[ClassDcl-pass2]{Class decls pass 2: default methods}
-%* *
-%************************************************************************
-
-The purpose of pass 2 is
-\begin{enumerate}
-\item
-to beat on the explicitly-provided default-method decls (if any),
-using them to produce a complete set of default-method decls.
-(Omitted ones elicit an error message.)
-\item
-to produce a definition for the selector function for each method
-and superclass dictionary.
-\end{enumerate}
-
-Pass~2 only applies to locally-defined class declarations.
-
-The function @tcClassDecls2@ just arranges to apply @tcClassDecl2@ to
-each local class decl.
-
-\begin{code}
-tcClassDecls2 :: [RenamedHsDecl]
- -> NF_TcM s (LIE, TcMonoBinds)
-
-tcClassDecls2 decls
- = foldr combine
- (returnNF_Tc (emptyLIE, EmptyMonoBinds))
- [tcClassDecl2 cls_decl | TyClD cls_decl <- decls, isClassDecl cls_decl]
+ ; returnM (op, all_generic)
+ }
where
- combine tc1 tc2 = tc1 `thenNF_Tc` \ (lie1, binds1) ->
- tc2 `thenNF_Tc` \ (lie2, binds2) ->
- returnNF_Tc (lie1 `plusLIE` lie2,
- binds1 `AndMonoBinds` binds2)
-\end{code}
-
-@tcClassDecl2@ is the business end of things.
-
-\begin{code}
-tcClassDecl2 :: RenamedTyClDecl -- The class declaration
- -> NF_TcM s (LIE, TcMonoBinds)
-
-tcClassDecl2 (ClassDecl context class_name
- tyvar_names _ class_sigs default_binds pragmas _ _ _ _ src_loc)
-
- | not (isLocallyDefined class_name)
- = returnNF_Tc (emptyLIE, EmptyMonoBinds)
-
- | otherwise -- It is locally defined
- = recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyMonoBinds)) $
- tcAddSrcLoc src_loc $
- tcLookupTy class_name `thenNF_Tc` \ (AClass clas) ->
- tcDefaultMethodBinds clas default_binds class_sigs
+ n_generic = count (isJust . maybeGenericMatch) matches
+ none_generic = n_generic == 0
+ all_generic = matches `lengthIs` n_generic
+
+
+tcClassSig :: NameEnv Bool -- Info about default methods;
+ -> LSig Name
+ -> TcM TcMethInfo
+
+tcClassSig dm_env (L loc (TypeSig (L _ op_name) op_hs_ty))
+ = setSrcSpan loc $ do
+ { op_ty <- tcHsKindedType op_hs_ty -- Class tyvars already in scope
+ ; let dm = case lookupNameEnv dm_env op_name of
+ Nothing -> NoDefMeth
+ Just False -> DefMeth
+ Just True -> GenDefMeth
+ ; returnM (op_name, dm, op_ty) }
\end{code}
-\begin{code}
-mkImplicitClassBinds :: [Class] -> NF_TcM s ([Id], TcMonoBinds)
-mkImplicitClassBinds classes
- = returnNF_Tc (concat cls_ids_s, andMonoBindList binds_s)
- -- The selector binds are already in the selector Id's unfoldings
- -- We don't return the data constructor etc from the class,
- -- because that's done via the class's TyCon
- where
- (cls_ids_s, binds_s) = unzip (map mk_implicit classes)
-
- mk_implicit clas = (sel_ids, binds)
- where
- sel_ids = classSelIds clas
- binds | isLocallyDefined clas = idsToMonoBinds sel_ids
- | otherwise = EmptyMonoBinds
-\end{code}
%************************************************************************
%* *
dfoo_list
\end{verbatim}
-\begin{code}
-tcDefaultMethodBinds
- :: Class
- -> RenamedMonoBinds
- -> [RenamedSig]
- -> TcM s (LIE, TcMonoBinds)
-
-tcDefaultMethodBinds clas default_binds sigs
- = -- Check that the default bindings come from this class
- checkFromThisClass clas default_binds `thenNF_Tc_`
-
- -- Do each default method separately
- -- For Hugs compatibility we make a default-method for every
- -- class op, regardless of whether or not the programmer supplied an
- -- explicit default decl for the class. GHC will actually never
- -- call the default method for such operations, because it'll whip up
- -- a more-informative default method at each instance decl.
- mapAndUnzipTc tc_dm op_items `thenTc` \ (defm_binds, const_lies) ->
-
- returnTc (plusLIEs const_lies, andMonoBindList defm_binds)
- where
- prags = filter isPragSig sigs
-
- (tyvars, _, _, op_items) = classBigSig clas
+@tcClassDecls2@ generates bindings for polymorphic default methods
+(generic default methods have by now turned into instance declarations)
- origin = ClassDeclOrigin
-
- -- We make a separate binding for each default method.
- -- At one time I used a single AbsBinds for all of them, thus
- -- AbsBind [d] [dm1, dm2, dm3] { dm1 = ...; dm2 = ...; dm3 = ... }
- -- But that desugars into
- -- ds = \d -> (..., ..., ...)
- -- dm1 = \d -> case ds d of (a,b,c) -> a
- -- And since ds is big, it doesn't get inlined, so we don't get good
- -- default methods. Better to make separate AbsBinds for each
-
- tc_dm op_item@(_, dm_id, _)
- = tcInstTyVars tyvars `thenNF_Tc` \ (clas_tyvars, inst_tys, _) ->
- let
- theta = [(mkClassPred clas inst_tys)]
- in
- newDicts origin theta `thenNF_Tc` \ (this_dict, [this_dict_id]) ->
- let
- avail_insts = this_dict
- in
- tcExtendTyVarEnvForMeths tyvars clas_tyvars (
- tcMethodBind clas origin clas_tyvars inst_tys theta
- default_binds prags False
- op_item
- ) `thenTc` \ (defm_bind, insts_needed, (_, local_dm_id)) ->
+\begin{code}
+tcClassDecl2 :: LTyClDecl Name -- The class declaration
+ -> TcM (LHsBinds Id, [Id])
+
+tcClassDecl2 (L loc (ClassDecl {tcdLName = class_name, tcdSigs = sigs,
+ tcdMeths = default_binds}))
+ = recoverM (returnM (emptyLHsBinds, [])) $
+ setSrcSpan loc $
+ tcLookupLocatedClass class_name `thenM` \ clas ->
+
+ -- We make a separate binding for each default method.
+ -- At one time I used a single AbsBinds for all of them, thus
+ -- AbsBind [d] [dm1, dm2, dm3] { dm1 = ...; dm2 = ...; dm3 = ... }
+ -- But that desugars into
+ -- ds = \d -> (..., ..., ...)
+ -- dm1 = \d -> case ds d of (a,b,c) -> a
+ -- And since ds is big, it doesn't get inlined, so we don't get good
+ -- default methods. Better to make separate AbsBinds for each
+ let
+ (tyvars, _, _, op_items) = classBigSig clas
+ prag_fn = mkPragFun sigs
+ tc_dm = tcDefMeth clas tyvars default_binds prag_fn
+
+ dm_sel_ids = [sel_id | (sel_id, DefMeth) <- op_items]
+ -- Generate code for polymorphic default methods only
+ -- (Generic default methods have turned into instance decls by now.)
+ -- This is incompatible with Hugs, which expects a polymorphic
+ -- default method for every class op, regardless of whether or not
+ -- the programmer supplied an explicit default decl for the class.
+ -- (If necessary we can fix that, but we don't have a convenient Id to hand.)
+ in
+ mapAndUnzipM tc_dm dm_sel_ids `thenM` \ (defm_binds, dm_ids_s) ->
+ returnM (listToBag defm_binds, concat dm_ids_s)
- tcAddErrCtxt (defltMethCtxt clas) $
+tcDefMeth clas tyvars binds_in prag_fn sel_id
+ = do { dm_name <- lookupTopBndrRn (mkDefMethRdrName sel_id)
+ ; let rigid_info = ClsSkol clas
+ clas_tyvars = tcSkolSigTyVars rigid_info tyvars
+ inst_tys = mkTyVarTys clas_tyvars
+ dm_ty = idType sel_id -- Same as dict selector!
+ theta = [mkClassPred clas inst_tys]
+ local_dm_id = mkDefaultMethodId dm_name dm_ty
+ origin = SigOrigin rigid_info
+
+ ; (_, meth_info) <- mkMethodBind origin clas inst_tys binds_in (sel_id, DefMeth)
+ ; [this_dict] <- newDicts origin theta
+ ; (defm_bind, insts_needed) <- getLIE (tcMethodBind clas_tyvars theta
+ [this_dict] prag_fn meth_info)
- -- tcMethodBind has checked that the class_tyvars havn't
- -- been unified with each other or another type, but we must
- -- still zonk them before passing them to tcSimplifyAndCheck
- zonkTcSigTyVars clas_tyvars `thenNF_Tc` \ clas_tyvars' ->
+ ; addErrCtxt (defltMethCtxt clas) $ do
- -- Check the context
- tcSimplifyAndCheck
- (ptext SLIT("class") <+> ppr clas)
- (mkVarSet clas_tyvars')
- avail_insts
- insts_needed `thenTc` \ (const_lie, dict_binds) ->
+ -- Check the context
+ { dict_binds <- tcSimplifyCheck
+ (ptext SLIT("class") <+> ppr clas)
+ clas_tyvars
+ [this_dict]
+ insts_needed
+
+ -- Simplification can do unification
+ ; checkSigTyVars clas_tyvars
- let
- full_bind = AbsBinds
- clas_tyvars'
- [this_dict_id]
- [(clas_tyvars', dm_id, local_dm_id)]
- emptyNameSet -- No inlines (yet)
- (dict_binds `andMonoBinds` defm_bind)
- in
- returnTc (full_bind, const_lie)
+ ; let
+ (_,dm_inst_id,_) = meth_info
+ full_bind = AbsBinds
+ clas_tyvars
+ [instToId this_dict]
+ [(clas_tyvars, local_dm_id, dm_inst_id, [])]
+ -- No inlines (yet)
+ (dict_binds `unionBags` defm_bind)
+ ; returnM (noLoc full_bind, [local_dm_id]) }}
+
+mkDefMethRdrName :: Id -> RdrName
+mkDefMethRdrName sel_id = mkDerivedRdrName (idName sel_id) mkDefaultMethodOcc
\end{code}
-\begin{code}
-checkFromThisClass :: Class -> RenamedMonoBinds -> NF_TcM s ()
-checkFromThisClass clas mbinds
- = mapNF_Tc check_from_this_class bndrs_w_locs `thenNF_Tc_`
- returnNF_Tc ()
- where
- check_from_this_class (bndr, loc)
- | nameOccName bndr `elem` sel_names = returnNF_Tc ()
- | otherwise = tcAddSrcLoc loc $
- addErrTc (badMethodErr bndr clas)
- sel_names = map getOccName (classSelIds clas)
- bndrs_w_locs = bagToList (collectMonoBinders mbinds)
-\end{code}
-
+
+%************************************************************************
+%* *
+\subsection{Typechecking a method}
+%* *
+%************************************************************************
@tcMethodBind@ is used to type-check both default-method and
instance-decl method declarations. We must type-check methods one at a
tyvar sets.
\begin{code}
+type MethodSpec = (Id, -- Global selector Id
+ Id, -- Local Id (class tyvars instantiated)
+ LHsBind Name) -- Binding for the method
+
tcMethodBind
- :: Class
- -> InstOrigin
- -> [TcTyVar] -- Instantiated type variables for the
- -- enclosing class/instance decl.
- -- They'll be signature tyvars, and we
- -- want to check that they don't get bound
- -> [TcType] -- Instance types
- -> TcThetaType -- Available theta; this could be used to check
- -- the method signature, but actually that's done by
- -- the caller; here, it's just used for the error message
- -> RenamedMonoBinds -- Method binding (pick the right one from in here)
- -> [RenamedSig] -- Pramgas (just for this one)
- -> Bool -- True <=> This method is from an instance declaration
- -> ClassOpItem -- The method selector and default-method Id
- -> TcM s (TcMonoBinds, LIE, (LIE, TcId))
-
-tcMethodBind clas origin inst_tyvars inst_tys inst_theta
- meth_binds prags is_inst_decl
- (sel_id, dm_id, explicit_dm)
- = tcGetSrcLoc `thenNF_Tc` \ loc ->
-
- newMethod origin sel_id inst_tys `thenNF_Tc` \ meth@(_, meth_id) ->
- mkTcSig meth_id loc `thenNF_Tc` \ sig_info ->
-
- let
- meth_name = idName meth_id
- maybe_user_bind = find_bind meth_name meth_binds
-
- no_user_bind = case maybe_user_bind of {Nothing -> True; other -> False}
-
- meth_bind = case maybe_user_bind of
- Just bind -> bind
- Nothing -> mk_default_bind meth_name loc
-
- meth_prags = find_prags meth_name prags
- in
-
- -- Warn if no method binding, only if -fwarn-missing-methods
- warnTc (is_inst_decl && opt_WarnMissingMethods && no_user_bind && not explicit_dm)
- (omittedMethodWarn sel_id clas) `thenNF_Tc_`
-
- -- Check the bindings; first add inst_tyvars to the envt
+ :: [TcTyVar] -- Skolemised type variables for the
+ -- enclosing class/instance decl.
+ -- They'll be signature tyvars, and we
+ -- want to check that they don't get bound
+ -- Also they are scoped, so we bring them into scope
+ -- Always equal the range of the type envt
+ -> TcThetaType -- Available theta; it's just used for the error message
+ -> [Inst] -- Available from context, used to simplify constraints
+ -- from the method body
+ -> TcPragFun -- Pragmas (e.g. inline pragmas)
+ -> MethodSpec -- Details of this method
+ -> TcM (LHsBinds Id)
+
+tcMethodBind inst_tyvars inst_theta avail_insts prag_fn
+ (sel_id, meth_id, meth_bind)
+ = recoverM (returnM emptyLHsBinds) $
+ -- If anything fails, recover returning no bindings.
+ -- This is particularly useful when checking the default-method binding of
+ -- a class decl. If we don't recover, we don't add the default method to
+ -- the type enviroment, and we get a tcLookup failure on $dmeth later.
+
+ -- Check the bindings; first adding inst_tyvars to the envt
-- so that we don't quantify over them in nested places
- -- The *caller* put the class/inst decl tyvars into the envt
- tcExtendGlobalTyVars (mkVarSet inst_tyvars) (
- tcAddErrCtxt (methodCtxt sel_id) $
- tcBindWithSigs NotTopLevel meth_bind
- [sig_info] meth_prags NonRecursive
- ) `thenTc` \ (binds, insts, _) ->
+
+ let -- Fake up a TcSigInfo to pass to tcMonoBinds
+ rigid_info = SigSkol (idName meth_id)
+ in
+ tcSkolType rigid_info (idType meth_id) `thenM` \ (tyvars', theta', tau') ->
+ getInstLoc (SigOrigin rigid_info) `thenM` \ loc ->
+ let meth_sig = TcSigInfo { sig_id = meth_id, sig_tvs = tyvars', sig_scoped = [],
+ sig_theta = theta', sig_tau = tau', sig_loc = loc }
+ lookup_sig name = ASSERT( name == idName meth_id )
+ Just meth_sig
+ in
+ tcExtendTyVarEnv inst_tyvars (
+ addErrCtxt (methodCtxt sel_id) $
+ getLIE $
+ tcMonoBinds [meth_bind] lookup_sig Recursive
+ ) `thenM` \ ((meth_bind, mono_bind_infos), meth_lie) ->
+
+ -- Now do context reduction. We simplify wrt both the local tyvars
+ -- and the ones of the class/instance decl, so that there is
+ -- no problem with
+ -- class C a where
+ -- op :: Eq a => a -> b -> a
+ --
+ -- We do this for each method independently to localise error messages
- tcExtendLocalValEnv [(meth_name, meth_id)] (
- tcSpecSigs meth_prags
- ) `thenTc` \ (prag_binds1, prag_lie) ->
+ addErrCtxtM (sigCtxt sel_id inst_tyvars inst_theta (idType meth_id)) $
+ newDictsAtLoc (sig_loc meth_sig) (sig_theta meth_sig) `thenM` \ meth_dicts ->
+ let
+ meth_tvs = sig_tvs meth_sig
+ all_tyvars = meth_tvs ++ inst_tyvars
+ all_insts = avail_insts ++ meth_dicts
+ sel_name = idName sel_id
+ in
+ tcSimplifyCheck
+ (ptext SLIT("class or instance method") <+> quotes (ppr sel_id))
+ all_tyvars all_insts meth_lie `thenM` \ lie_binds ->
- -- The prag_lie for a SPECIALISE pragma will mention the function
- -- itself, so we have to simplify them away right now lest they float
- -- outwards!
- bindInstsOfLocalFuns prag_lie [meth_id] `thenTc` \ (prag_lie', prag_binds2) ->
+ checkSigTyVars all_tyvars `thenM_`
+ tcPrags meth_id (prag_fn sel_name) `thenM` \ prags ->
+ let
+ [(_,_,local_meth_id)] = mono_bind_infos
+ poly_meth_bind = noLoc $ AbsBinds meth_tvs
+ (map instToId meth_dicts)
+ [(meth_tvs, meth_id, local_meth_id, prags)]
+ (lie_binds `unionBags` meth_bind)
+ in
+ returnM (unitBag poly_meth_bind)
- -- Now check that the instance type variables
- -- (or, in the case of a class decl, the class tyvars)
- -- have not been unified with anything in the environment
- --
- -- We do this for each method independently to localise error messages
- tcAddErrCtxtM (sigCtxt sig_msg inst_tyvars inst_theta (idType meth_id)) $
- checkSigTyVars inst_tyvars emptyVarSet `thenTc_`
-
- returnTc (binds `AndMonoBinds` prag_binds1 `AndMonoBinds` prag_binds2,
- insts `plusLIE` prag_lie',
- meth)
- where
- sig_msg = ptext SLIT("When checking the expected type for class method") <+> ppr sel_name
-
- sel_name = idName sel_id
-
- -- The renamer just puts the selector ID as the binder in the method binding
- -- but we must use the method name; so we substitute it here. Crude but simple.
- find_bind meth_name (FunMonoBind op_name fix matches loc)
- | op_name == sel_name = Just (FunMonoBind meth_name fix matches loc)
- find_bind meth_name (AndMonoBinds b1 b2)
- = find_bind meth_name b1 `seqMaybe` find_bind meth_name b2
- find_bind meth_name other = Nothing -- Default case
-
-
- -- Find the prags for this method, and replace the
- -- selector name with the method name
- find_prags meth_name [] = []
- find_prags meth_name (SpecSig name ty loc : prags)
- | name == sel_name = SpecSig meth_name ty loc : find_prags meth_name prags
- find_prags meth_name (InlineSig name phase loc : prags)
- | name == sel_name = InlineSig meth_name phase loc : find_prags meth_name prags
- find_prags meth_name (NoInlineSig name phase loc : prags)
- | name == sel_name = NoInlineSig meth_name phase loc : find_prags meth_name prags
- find_prags meth_name (prag:prags) = find_prags meth_name prags
-
- mk_default_bind local_meth_name loc
- = FunMonoBind local_meth_name
- False -- Not infix decl
- [mkSimpleMatch [] (default_expr loc) Nothing loc]
- loc
-
- default_expr loc
- | explicit_dm = HsVar (getName dm_id) -- There's a default method
- | otherwise = error_expr loc -- No default method
-
- error_expr loc = HsApp (HsVar (getName nO_METHOD_BINDING_ERROR_ID))
- (HsLit (HsString (_PK_ (error_msg loc))))
-
- error_msg loc = showSDoc (hcat [ppr loc, text "|", ppr sel_id ])
+
+mkMethodBind :: InstOrigin
+ -> Class -> [TcType] -- Class and instance types
+ -> LHsBinds Name -- Method binding (pick the right one from in here)
+ -> ClassOpItem
+ -> TcM (Maybe Inst, -- Method inst
+ MethodSpec)
+-- Find the binding for the specified method, or make
+-- up a suitable default method if it isn't there
+
+mkMethodBind origin clas inst_tys meth_binds (sel_id, dm_info)
+ = mkMethId origin clas sel_id inst_tys `thenM` \ (mb_inst, meth_id) ->
+ let
+ meth_name = idName meth_id
+ in
+ -- Figure out what method binding to use
+ -- If the user suppplied one, use it, else construct a default one
+ getSrcSpanM `thenM` \ loc ->
+ (case find_bind (idName sel_id) meth_name meth_binds of
+ Just user_bind -> returnM user_bind
+ Nothing ->
+ mkDefMethRhs origin clas inst_tys sel_id loc dm_info `thenM` \ rhs ->
+ -- Not infix decl
+ returnM (noLoc $ FunBind (noLoc meth_name) False
+ (mkMatchGroup [mkSimpleMatch [] rhs])
+ placeHolderNames)
+ ) `thenM` \ meth_bind ->
+
+ returnM (mb_inst, (sel_id, meth_id, meth_bind))
+
+mkMethId :: InstOrigin -> Class
+ -> Id -> [TcType] -- Selector, and instance types
+ -> TcM (Maybe Inst, Id)
+
+-- mkMethId instantiates the selector Id at the specified types
+mkMethId origin clas sel_id inst_tys
+ = let
+ (tyvars,rho) = tcSplitForAllTys (idType sel_id)
+ rho_ty = ASSERT( length tyvars == length inst_tys )
+ substTyWith tyvars inst_tys rho
+ (preds,tau) = tcSplitPhiTy rho_ty
+ first_pred = head preds
+ in
+ -- The first predicate should be of form (C a b)
+ -- where C is the class in question
+ ASSERT( not (null preds) &&
+ case getClassPredTys_maybe first_pred of
+ { Just (clas1,tys) -> clas == clas1 ; Nothing -> False }
+ )
+ if isSingleton preds then
+ -- If it's the only one, make a 'method'
+ getInstLoc origin `thenM` \ inst_loc ->
+ newMethod inst_loc sel_id inst_tys preds tau `thenM` \ meth_inst ->
+ returnM (Just meth_inst, instToId meth_inst)
+ else
+ -- If it's not the only one we need to be careful
+ -- For example, given 'op' defined thus:
+ -- class Foo a where
+ -- op :: (?x :: String) => a -> a
+ -- (mkMethId op T) should return an Inst with type
+ -- (?x :: String) => T -> T
+ -- That is, the class-op's context is still there.
+ -- BUT: it can't be a Method any more, because it breaks
+ -- INVARIANT 2 of methods. (See the data decl for Inst.)
+ newUnique `thenM` \ uniq ->
+ getSrcSpanM `thenM` \ loc ->
+ let
+ real_tau = mkPhiTy (tail preds) tau
+ meth_id = mkUserLocal (getOccName sel_id) uniq real_tau
+ (srcSpanStart loc) --TODO
+ in
+ returnM (Nothing, meth_id)
+
+ -- The user didn't supply a method binding,
+ -- so we have to make up a default binding
+ -- The RHS of a default method depends on the default-method info
+mkDefMethRhs origin clas inst_tys sel_id loc DefMeth
+ = -- An polymorphic default method
+ lookupImportedName (mkDefMethRdrName sel_id) `thenM` \ dm_name ->
+ -- Might not be imported, but will be an OrigName
+ traceRn (text "mkDefMeth" <+> ppr dm_name) `thenM_`
+ returnM (nlHsVar dm_name)
+
+mkDefMethRhs origin clas inst_tys sel_id loc NoDefMeth
+ = -- No default method
+ -- Warn only if -fwarn-missing-methods
+ doptM Opt_WarnMissingMethods `thenM` \ warn ->
+ warnTc (isInstDecl origin
+ && warn
+ && reportIfUnused (getOccName sel_id))
+ (omittedMethodWarn sel_id) `thenM_`
+ returnM error_rhs
+ where
+ error_rhs = noLoc $ HsLam (mkMatchGroup [mkSimpleMatch wild_pats simple_rhs])
+ simple_rhs = nlHsApp (nlHsVar (getName nO_METHOD_BINDING_ERROR_ID))
+ (nlHsLit (HsStringPrim (mkFastString error_msg)))
+ error_msg = showSDoc (hcat [ppr loc, text "|", ppr sel_id ])
+
+ -- When the type is of form t1 -> t2 -> t3
+ -- make a default method like (\ _ _ -> noMethBind "blah")
+ -- rather than simply (noMethBind "blah")
+ -- Reason: if t1 or t2 are higher-ranked types we get n
+ -- silly ambiguity messages.
+ -- Example: f :: (forall a. Eq a => a -> a) -> Int
+ -- f = error "urk"
+ -- Here, tcSub tries to force (error "urk") to have the right type,
+ -- thus: f = \(x::forall a. Eq a => a->a) -> error "urk" (x t)
+ -- where 't' is fresh ty var. This leads directly to "ambiguous t".
+ --
+ -- NB: technically this changes the meaning of the default-default
+ -- method slightly, because `seq` can see the lambdas. Oh well.
+ (_,_,tau1) = tcSplitSigmaTy (idType sel_id)
+ (_,_,tau2) = tcSplitSigmaTy tau1
+ -- Need two splits because the selector can have a type like
+ -- forall a. Foo a => forall b. Eq b => ...
+ (arg_tys, _) = tcSplitFunTys tau2
+ wild_pats = [nlWildPat | ty <- arg_tys]
+
+mkDefMethRhs origin clas inst_tys sel_id loc GenDefMeth
+ = -- A generic default method
+ -- If the method is defined generically, we can only do the job if the
+ -- instance declaration is for a single-parameter type class with
+ -- a type constructor applied to type arguments in the instance decl
+ -- (checkTc, so False provokes the error)
+ ASSERT( isInstDecl origin ) -- We never get here from a class decl
+ do { checkTc (isJust maybe_tycon)
+ (badGenericInstance sel_id (notSimple inst_tys))
+ ; checkTc (tyConHasGenerics tycon)
+ (badGenericInstance sel_id (notGeneric tycon))
+
+ ; dflags <- getDOpts
+ ; ioToTcRn (dumpIfSet_dyn dflags Opt_D_dump_deriv "Filling in method body"
+ (vcat [ppr clas <+> ppr inst_tys,
+ nest 2 (ppr sel_id <+> equals <+> ppr rhs)]))
+
+ -- Rename it before returning it
+ ; (rn_rhs, _) <- rnLExpr rhs
+ ; returnM rn_rhs }
+ where
+ rhs = mkGenericRhs sel_id clas_tyvar tycon
+
+ -- The tycon is only used in the generic case, and in that
+ -- case we require that the instance decl is for a single-parameter
+ -- type class with type variable arguments:
+ -- instance (...) => C (T a b)
+ clas_tyvar = head (classTyVars clas)
+ Just tycon = maybe_tycon
+ maybe_tycon = case inst_tys of
+ [ty] -> case tcSplitTyConApp_maybe ty of
+ Just (tycon, arg_tys) | all tcIsTyVarTy arg_tys -> Just tycon
+ other -> Nothing
+ other -> Nothing
+
+isInstDecl (SigOrigin (InstSkol _)) = True
+isInstDecl (SigOrigin (ClsSkol _)) = False
\end{code}
-Contexts and errors
-~~~~~~~~~~~~~~~~~~~
+
\begin{code}
-classArityErr class_name
- = ptext SLIT("Too many parameters for class") <+> quotes (ppr class_name)
+-- The renamer just puts the selector ID as the binder in the method binding
+-- but we must use the method name; so we substitute it here. Crude but simple.
+find_bind sel_name meth_name binds
+ = foldlBag seqMaybe Nothing (mapBag f binds)
+ where
+ f (L loc1 (FunBind (L loc2 op_name) fix matches fvs)) | op_name == sel_name
+ = Just (L loc1 (FunBind (L loc2 meth_name) fix matches fvs))
+ f _other = Nothing
+\end{code}
-superClassErr class_name sc
- = ptext SLIT("Illegal superclass constraint") <+> quotes (ppr sc)
- <+> ptext SLIT("in declaration for class") <+> quotes (ppr class_name)
-defltMethCtxt class_name
- = ptext SLIT("When checking the default methods for class") <+> quotes (ppr class_name)
+%************************************************************************
+%* *
+\subsection{Extracting generic instance declaration from class declarations}
+%* *
+%************************************************************************
+
+@getGenericInstances@ extracts the generic instance declarations from a class
+declaration. For exmaple
+
+ class C a where
+ op :: a -> a
+
+ op{ x+y } (Inl v) = ...
+ op{ x+y } (Inr v) = ...
+ op{ x*y } (v :*: w) = ...
+ op{ 1 } Unit = ...
+
+gives rise to the instance declarations
+
+ instance C (x+y) where
+ op (Inl v) = ...
+ op (Inr v) = ...
+
+ instance C (x*y) where
+ op (v :*: w) = ...
+
+ instance C 1 where
+ op Unit = ...
+
+
+\begin{code}
+getGenericInstances :: [LTyClDecl Name] -> TcM [InstInfo]
+getGenericInstances class_decls
+ = do { gen_inst_infos <- mappM (addLocM get_generics) class_decls
+ ; let { gen_inst_info = concat gen_inst_infos }
+
+ -- Return right away if there is no generic stuff
+ ; if null gen_inst_info then returnM []
+ else do
+
+ -- Otherwise print it out
+ { dflags <- getDOpts
+ ; ioToTcRn (dumpIfSet_dyn dflags Opt_D_dump_deriv "Generic instances"
+ (vcat (map pprInstInfoDetails gen_inst_info)))
+ ; returnM gen_inst_info }}
+
+get_generics decl@(ClassDecl {tcdLName = class_name, tcdMeths = def_methods})
+ | null generic_binds
+ = returnM [] -- The comon case: no generic default methods
+
+ | otherwise -- A source class decl with generic default methods
+ = recoverM (returnM []) $
+ tcAddDeclCtxt decl $
+ tcLookupLocatedClass class_name `thenM` \ clas ->
+
+ -- Group by type, and
+ -- make an InstInfo out of each group
+ let
+ groups = groupWith listToBag generic_binds
+ in
+ mappM (mkGenericInstance clas) groups `thenM` \ inst_infos ->
+
+ -- Check that there is only one InstInfo for each type constructor
+ -- The main way this can fail is if you write
+ -- f {| a+b |} ... = ...
+ -- f {| x+y |} ... = ...
+ -- Then at this point we'll have an InstInfo for each
+ let
+ tc_inst_infos :: [(TyCon, InstInfo)]
+ tc_inst_infos = [(simpleInstInfoTyCon i, i) | i <- inst_infos]
+
+ bad_groups = [group | group <- equivClassesByUniq get_uniq tc_inst_infos,
+ group `lengthExceeds` 1]
+ get_uniq (tc,_) = getUnique tc
+ in
+ mappM (addErrTc . dupGenericInsts) bad_groups `thenM_`
+
+ -- Check that there is an InstInfo for each generic type constructor
+ let
+ missing = genericTyConNames `minusList` [tyConName tc | (tc,_) <- tc_inst_infos]
+ in
+ checkTc (null missing) (missingGenericInstances missing) `thenM_`
+
+ returnM inst_infos
+ where
+ generic_binds :: [(HsType Name, LHsBind Name)]
+ generic_binds = getGenericBinds def_methods
+
+
+---------------------------------
+getGenericBinds :: LHsBinds Name -> [(HsType Name, LHsBind Name)]
+ -- Takes a group of method bindings, finds the generic ones, and returns
+ -- them in finite map indexed by the type parameter in the definition.
+getGenericBinds binds = concat (map getGenericBind (bagToList binds))
+
+getGenericBind (L loc (FunBind id infixop (MatchGroup matches ty) fvs))
+ = groupWith wrap (mapCatMaybes maybeGenericMatch matches)
+ where
+ wrap ms = L loc (FunBind id infixop (MatchGroup ms ty) fvs)
+getGenericBind _
+ = []
+
+groupWith :: ([a] -> b) -> [(HsType Name, a)] -> [(HsType Name, b)]
+groupWith op [] = []
+groupWith op ((t,v):prs) = (t, op (v:vs)) : groupWith op rest
+ where
+ vs = map snd this
+ (this,rest) = partition same_t prs
+ same_t (t',v) = t `eqPatType` t'
+
+eqPatLType :: LHsType Name -> LHsType Name -> Bool
+eqPatLType t1 t2 = unLoc t1 `eqPatType` unLoc t2
+
+eqPatType :: HsType Name -> HsType Name -> Bool
+-- A very simple equality function, only for
+-- type patterns in generic function definitions.
+eqPatType (HsTyVar v1) (HsTyVar v2) = v1==v2
+eqPatType (HsAppTy s1 t1) (HsAppTy s2 t2) = s1 `eqPatLType` s2 && t2 `eqPatLType` t2
+eqPatType (HsOpTy s1 op1 t1) (HsOpTy s2 op2 t2) = s1 `eqPatLType` s2 && t2 `eqPatLType` t2 && unLoc op1 == unLoc op2
+eqPatType (HsNumTy n1) (HsNumTy n2) = n1 == n2
+eqPatType (HsParTy t1) t2 = unLoc t1 `eqPatType` t2
+eqPatType t1 (HsParTy t2) = t1 `eqPatType` unLoc t2
+eqPatType _ _ = False
+
+---------------------------------
+mkGenericInstance :: Class
+ -> (HsType Name, LHsBinds Name)
+ -> TcM InstInfo
+
+mkGenericInstance clas (hs_ty, binds)
+ -- Make a generic instance declaration
+ -- For example: instance (C a, C b) => C (a+b) where { binds }
+
+ = -- Extract the universally quantified type variables
+ -- and wrap them as forall'd tyvars, so that kind inference
+ -- works in the standard way
+ let
+ sig_tvs = map (noLoc.UserTyVar) (nameSetToList (extractHsTyVars (noLoc hs_ty)))
+ hs_forall_ty = noLoc $ mkExplicitHsForAllTy sig_tvs (noLoc []) (noLoc hs_ty)
+ in
+ -- Type-check the instance type, and check its form
+ tcHsSigType GenPatCtxt hs_forall_ty `thenM` \ forall_inst_ty ->
+ let
+ (tyvars, inst_ty) = tcSplitForAllTys forall_inst_ty
+ in
+ checkTc (validGenericInstanceType inst_ty)
+ (badGenericInstanceType binds) `thenM_`
+
+ -- Make the dictionary function.
+ getSrcSpanM `thenM` \ span ->
+ getOverlapFlag `thenM` \ overlap_flag ->
+ newDFunName clas [inst_ty] (srcSpanStart span) `thenM` \ dfun_name ->
+ let
+ inst_theta = [mkClassPred clas [mkTyVarTy tv] | tv <- tyvars]
+ dfun_id = mkDictFunId dfun_name tyvars inst_theta clas [inst_ty]
+ ispec = mkLocalInstance dfun_id overlap_flag
+ in
+ returnM (InstInfo { iSpec = ispec, iBinds = VanillaInst binds [] })
+\end{code}
+
+
+%************************************************************************
+%* *
+ Error messages
+%* *
+%************************************************************************
+
+\begin{code}
+tcAddDeclCtxt decl thing_inside
+ = addErrCtxt ctxt thing_inside
+ where
+ thing = case decl of
+ ClassDecl {} -> "class"
+ TySynonym {} -> "type synonym"
+ TyData {tcdND = NewType} -> "newtype"
+ TyData {tcdND = DataType} -> "data type"
+
+ ctxt = hsep [ptext SLIT("In the"), text thing,
+ ptext SLIT("declaration for"), quotes (ppr (tcdName decl))]
+
+defltMethCtxt clas
+ = ptext SLIT("When checking the default methods for class") <+> quotes (ppr clas)
methodCtxt sel_id
= ptext SLIT("In the definition for method") <+> quotes (ppr sel_id)
-badMethodErr bndr clas
+badMethodErr clas op
= hsep [ptext SLIT("Class"), quotes (ppr clas),
- ptext SLIT("does not have a method"), quotes (ppr bndr)]
-
-omittedMethodWarn sel_id clas
- = sep [ptext SLIT("No explicit method nor default method for") <+> quotes (ppr sel_id),
- ptext SLIT("in an instance declaration for") <+> quotes (ppr clas)]
+ ptext SLIT("does not have a method"), quotes (ppr op)]
+
+omittedMethodWarn sel_id
+ = ptext SLIT("No explicit method nor default method for") <+> quotes (ppr sel_id)
+
+badGenericInstance sel_id because
+ = sep [ptext SLIT("Can't derive generic code for") <+> quotes (ppr sel_id),
+ because]
+
+notSimple inst_tys
+ = vcat [ptext SLIT("because the instance type(s)"),
+ nest 2 (ppr inst_tys),
+ ptext SLIT("is not a simple type of form (T a b c)")]
+
+notGeneric tycon
+ = vcat [ptext SLIT("because the instance type constructor") <+> quotes (ppr tycon) <+>
+ ptext SLIT("was not compiled with -fgenerics")]
+
+badGenericInstanceType binds
+ = vcat [ptext SLIT("Illegal type pattern in the generic bindings"),
+ nest 4 (ppr binds)]
+
+missingGenericInstances missing
+ = ptext SLIT("Missing type patterns for") <+> pprQuotedList missing
+
+dupGenericInsts tc_inst_infos
+ = vcat [ptext SLIT("More than one type pattern for a single generic type constructor:"),
+ nest 4 (vcat (map ppr_inst_ty tc_inst_infos)),
+ ptext SLIT("All the type patterns for a generic type constructor must be identical")
+ ]
+ where
+ ppr_inst_ty (_,inst) = ppr (simpleInstInfoTy inst)
+
+mixedGenericErr op
+ = ptext SLIT("Can't mix generic and non-generic equations for class method") <+> quotes (ppr op)
\end{code}
projects / ghc-hetmet.git / blobdiff