X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=ghc%2Fcompiler%2Ftypecheck%2FTcInstDcls.lhs;h=76b87cee041eec3810d108241ab64896239ebdeb;hb=75c431d16d01cb3b01f8d81d0520f43b4f9bac50;hp=f171f16c1a41a45e7368ace7acff60e6743f635b;hpb=5e3f005d3012472e422d4ffd7dca5c21a80fca80;p=ghc-hetmet.git diff --git a/ghc/compiler/typecheck/TcInstDcls.lhs b/ghc/compiler/typecheck/TcInstDcls.lhs index f171f16..76b87ce 100644 --- a/ghc/compiler/typecheck/TcInstDcls.lhs +++ b/ghc/compiler/typecheck/TcInstDcls.lhs @@ -4,79 +4,75 @@ \section[TcInstDecls]{Typechecking instance declarations} \begin{code} -module TcInstDcls ( tcInstDecls1, tcInstDecls2, tcAddDeclCtxt ) where +module TcInstDcls ( tcInstDecls1, tcIfaceInstDecls1, addInstDFuns, + tcInstDecls2, initInstEnv, tcAddDeclCtxt ) where #include "HsVersions.h" import CmdLineOpts ( DynFlag(..) ) -import HsSyn ( HsDecl(..), InstDecl(..), TyClDecl(..), HsType(..), +import HsSyn ( InstDecl(..), TyClDecl(..), HsType(..), MonoBinds(..), HsExpr(..), HsLit(..), Sig(..), HsTyVarBndr(..), - andMonoBindList, collectMonoBinders, isClassDecl, toHsType + andMonoBindList, collectMonoBinders, + isClassDecl, toHsType ) -import RnHsSyn ( RenamedHsBinds, RenamedInstDecl, RenamedHsDecl, +import RnHsSyn ( RenamedHsBinds, RenamedInstDecl, RenamedMonoBinds, RenamedTyClDecl, RenamedHsType, extractHsTyVars, maybeGenericMatch ) import TcHsSyn ( TcMonoBinds, mkHsConApp ) import TcBinds ( tcSpecSigs ) -import TcClassDcl ( tcMethodBind, badMethodErr ) +import TcClassDcl ( tcMethodBind, mkMethodBind, badMethodErr ) import TcMonad -import TcMType ( tcInstSigTyVars, checkValidTheta, checkValidInstHead, instTypeErr, +import TcMType ( tcInstType, checkValidTheta, checkValidInstHead, instTypeErr, UserTypeCtxt(..), SourceTyCtxt(..) ) -import TcType ( tcSplitDFunTy, mkClassPred, mkTyVarTy, mkTyVarTys, - tcSplitSigmaTy, tcSplitPredTy_maybe, getClassPredTys, +import TcType ( mkClassPred, mkTyVarTy, tcSplitForAllTys, + tcSplitSigmaTy, getClassPredTys, tcSplitPredTy_maybe, TyVarDetails(..) ) -import Inst ( InstOrigin(..), - newDicts, instToId, +import Inst ( InstOrigin(..), newDicts, instToId, LIE, mkLIE, emptyLIE, plusLIE, plusLIEs ) import TcDeriv ( tcDeriving ) -import TcEnv ( TcEnv, tcExtendGlobalValEnv, - tcExtendTyVarEnvForMeths, - tcAddImportedIdInfo, tcLookupClass, +import TcEnv ( tcExtendGlobalValEnv, tcExtendLocalValEnv2, + tcLookupId, tcLookupClass, tcExtendTyVarEnv2, InstInfo(..), pprInstInfo, simpleInstInfoTyCon, - simpleInstInfoTy, newDFunName, - isLocalThing, + simpleInstInfoTy, newDFunName ) import InstEnv ( InstEnv, extendInstEnv ) import PprType ( pprClassPred ) -import TcMonoType ( tcHsTyVars, kcHsSigType, tcHsType, tcHsSigType ) +import TcMonoType ( tcSigPolyId, tcHsTyVars, kcHsSigType, tcHsType, tcHsSigType ) import TcUnify ( checkSigTyVars ) -import TcSimplify ( tcSimplifyCheck ) -import HscTypes ( HomeSymbolTable, DFunId, - ModDetails(..), PackageInstEnv, PersistentRenamerState +import TcSimplify ( tcSimplifyCheck, tcSimplifyTop ) +import HscTypes ( HomeSymbolTable, DFunId, FixityEnv, + PersistentCompilerState(..), PersistentRenamerState, + ModDetails(..) ) - -import Subst ( substTy, substTheta ) +import Subst ( mkTyVarSubst, substTheta ) import DataCon ( classDataCon ) import Class ( Class, classBigSig ) import Var ( idName, idType ) -import VarSet ( emptyVarSet ) import Id ( setIdLocalExported ) -import MkId ( mkDictFunId ) +import MkId ( mkDictFunId, unsafeCoerceId, rUNTIME_ERROR_ID ) import FunDeps ( checkInstFDs ) import Generics ( validGenericInstanceType ) import Module ( Module, foldModuleEnv ) import Name ( getSrcLoc ) import NameSet ( unitNameSet, emptyNameSet, nameSetToList ) -import PrelInfo ( eRROR_ID ) import TyCon ( TyCon ) -import Subst ( mkTopTyVarSubst, substTheta ) import TysWiredIn ( genericTyCons ) -import Name ( Name ) import SrcLoc ( SrcLoc ) import Unique ( Uniquable(..) ) -import Util ( lengthExceeds ) -import BasicTypes ( NewOrData(..), Fixity ) +import Util ( lengthExceeds, isSingleton ) +import BasicTypes ( NewOrData(..) ) +import UnicodeUtil ( stringToUtf8 ) import ErrUtils ( dumpIfSet_dyn ) import ListSetOps ( Assoc, emptyAssoc, plusAssoc_C, mapAssoc, - assocElts, extendAssoc_C, - equivClassesByUniq, minusList + assocElts, extendAssoc_C, equivClassesByUniq, minusList ) -import List ( partition ) +import Maybe ( catMaybes ) import Outputable +import FastString \end{code} Typechecking instance declarations is done in two passes. The first @@ -162,70 +158,70 @@ and $dbinds_super$ bind the superclass dictionaries sd1 \ldots sdm. Gather up the instance declarations from their various sources \begin{code} -tcInstDecls1 :: PackageInstEnv - -> PersistentRenamerState - -> HomeSymbolTable -- Contains instances - -> TcEnv -- Contains IdInfo for dfun ids - -> (Name -> Maybe Fixity) -- for deriving Show and Read - -> Module -- Module for deriving - -> [RenamedHsDecl] - -> TcM (PackageInstEnv, InstEnv, [InstInfo], RenamedHsBinds) - -tcInstDecls1 inst_env0 prs hst unf_env get_fixity this_mod decls - = let - inst_decls = [inst_decl | InstD inst_decl <- decls] - tycl_decls = [decl | TyClD decl <- decls] - clas_decls = filter isClassDecl tycl_decls - in +tcInstDecls1 -- Deal with source-code instance decls + :: PersistentRenamerState + -> InstEnv -- Imported instance envt + -> FixityEnv -- for deriving Show and Read + -> Module -- Module for deriving + -> [RenamedTyClDecl] -- For deriving stuff + -> [RenamedInstDecl] -- Source code instance decls + -> TcM (InstEnv, -- the full inst env + [InstInfo], -- instance decls to process; contains all dfuns + -- for this module + RenamedHsBinds) -- derived instances + +tcInstDecls1 prs inst_env get_fixity this_mod + tycl_decls inst_decls +-- The incoming inst_env includes all the imported instances already + = checkNoErrsTc $ + -- Stop if addInstInfos etc discovers any errors + -- (they recover, so that we get more than one error each round) -- (1) Do the ordinary instance declarations - mapNF_Tc tcInstDecl1 inst_decls `thenNF_Tc` \ inst_infos -> + mapNF_Tc tcLocalInstDecl1 inst_decls `thenNF_Tc` \ local_inst_infos -> + let + local_inst_info = catMaybes local_inst_infos + clas_decls = filter isClassDecl tycl_decls + in -- (2) Instances from generic class declarations getGenericInstances clas_decls `thenTc` \ generic_inst_info -> -- Next, construct the instance environment so far, consisting of - -- a) cached non-home-package InstEnv (gotten from pcs) pcs_insts pcs - -- b) imported instance decls (not in the home package) inst_env1 - -- c) other modules in this package (gotten from hst) inst_env2 - -- d) local instance decls inst_env3 - -- e) generic instances inst_env4 - -- The result of (b) replaces the cached InstEnv in the PCS - let - (local_inst_info, imported_inst_info) - = partition (isLocalThing this_mod . iDFunId) (concat inst_infos) - - imported_dfuns = map (tcAddImportedIdInfo unf_env . iDFunId) - imported_inst_info - hst_dfuns = foldModuleEnv ((++) . md_insts) [] hst - in - --- pprTrace "tcInstDecls" (vcat [ppr imported_dfuns, ppr hst_dfuns]) $ - - addInstDFuns inst_env0 imported_dfuns `thenNF_Tc` \ inst_env1 -> - addInstDFuns inst_env1 hst_dfuns `thenNF_Tc` \ inst_env2 -> - addInstInfos inst_env2 local_inst_info `thenNF_Tc` \ inst_env3 -> - addInstInfos inst_env3 generic_inst_info `thenNF_Tc` \ inst_env4 -> + -- a) imported instance decls (from this module) inst_env1 + -- b) local instance decls inst_env2 + -- c) generic instances final_inst_env + addInstInfos inst_env local_inst_info `thenNF_Tc` \ inst_env1 -> + addInstInfos inst_env1 generic_inst_info `thenNF_Tc` \ inst_env2 -> -- (3) Compute instances from "deriving" clauses; -- note that we only do derivings for things in this module; -- we ignore deriving decls from interfaces! -- This stuff computes a context for the derived instance decl, so it - -- needs to know about all the instances possible; hecne inst_env4 - tcDeriving prs this_mod inst_env4 get_fixity tycl_decls - `thenTc` \ (deriv_inst_info, deriv_binds) -> - addInstInfos inst_env4 deriv_inst_info `thenNF_Tc` \ final_inst_env -> + -- needs to know about all the instances possible; hence inst_env4 + tcDeriving prs this_mod inst_env2 + get_fixity tycl_decls `thenTc` \ (deriv_inst_info, deriv_binds) -> + addInstInfos inst_env2 deriv_inst_info `thenNF_Tc` \ final_inst_env -> - returnTc (inst_env1, - final_inst_env, + returnTc (final_inst_env, generic_inst_info ++ deriv_inst_info ++ local_inst_info, deriv_binds) +initInstEnv :: PersistentCompilerState -> HomeSymbolTable -> NF_TcM InstEnv +-- Initialise the instance environment from the +-- persistent compiler state and the home symbol table +initInstEnv pcs hst + = let + pkg_inst_env = pcs_insts pcs + hst_dfuns = foldModuleEnv ((++) . md_insts) [] hst + in + addInstDFuns pkg_inst_env hst_dfuns + addInstInfos :: InstEnv -> [InstInfo] -> NF_TcM InstEnv addInstInfos inst_env infos = addInstDFuns inst_env (map iDFunId infos) addInstDFuns :: InstEnv -> [DFunId] -> NF_TcM InstEnv addInstDFuns inst_env dfuns - = getDOptsTc `thenTc` \ dflags -> + = getDOptsTc `thenNF_Tc` \ dflags -> let (inst_env', errs) = extendInstEnv dflags inst_env dfuns in @@ -237,12 +233,31 @@ addInstDFuns inst_env dfuns \end{code} \begin{code} -tcInstDecl1 :: RenamedInstDecl -> NF_TcM [InstInfo] --- Deal with a single instance declaration --- Type-check all the stuff before the "where" -tcInstDecl1 decl@(InstDecl poly_ty binds uprags maybe_dfun_name src_loc) - = -- Prime error recovery, set source location - recoverNF_Tc (returnNF_Tc []) $ +tcIfaceInstDecls1 :: [RenamedInstDecl] -> NF_TcM [DFunId] +tcIfaceInstDecls1 decls = mapNF_Tc tcIfaceInstDecl1 decls + +tcIfaceInstDecl1 :: RenamedInstDecl -> NF_TcM DFunId + -- An interface-file instance declaration + -- Should be in scope by now, because we should + -- have sucked in its interface-file definition + -- So it will be replete with its unfolding etc +tcIfaceInstDecl1 decl@(InstDecl poly_ty binds uprags (Just dfun_name) src_loc) + = tcLookupId dfun_name + + +tcLocalInstDecl1 :: RenamedInstDecl + -> NF_TcM (Maybe InstInfo) -- Nothing if there was an error + -- A source-file instance declaration + -- Type-check all the stuff before the "where" + -- + -- We check for respectable instance type, and context + -- but only do this for non-imported instance decls. + -- Imported ones should have been checked already, and may indeed + -- contain something illegal in normal Haskell, notably + -- instance CCallable [Char] +tcLocalInstDecl1 decl@(InstDecl poly_ty binds uprags Nothing src_loc) + = -- Prime error recovery, set source location + recoverNF_Tc (returnNF_Tc Nothing) $ tcAddSrcLoc src_loc $ tcAddErrCtxt (instDeclCtxt poly_ty) $ @@ -252,29 +267,14 @@ tcInstDecl1 decl@(InstDecl poly_ty binds uprags maybe_dfun_name src_loc) tcHsType poly_ty `thenTc` \ poly_ty' -> let (tyvars, theta, tau) = tcSplitSigmaTy poly_ty' - (clas,inst_tys) = case tcSplitPredTy_maybe tau of { Just st -> getClassPredTys st } - -- The checkValidInstHead makes sure these splits succeed - in - (case maybe_dfun_name of - Nothing -> -- A source-file instance declaration - -- Check for respectable instance type, and context - -- but only do this for non-imported instance decls. - -- Imported ones should have been checked already, and may indeed - -- contain something illegal in normal Haskell, notably - -- instance CCallable [Char] - checkValidTheta InstThetaCtxt theta `thenTc_` - checkValidInstHead tau `thenTc_` - checkTc (checkInstFDs theta clas inst_tys) - (instTypeErr (pprClassPred clas inst_tys) msg) `thenTc_` - newDFunName clas inst_tys src_loc - - Just dfun_name -> -- An interface-file instance declaration - returnNF_Tc dfun_name - ) `thenNF_Tc` \ dfun_name -> - let - dfun_id = mkDictFunId dfun_name clas tyvars inst_tys theta in - returnTc [InstInfo { iDFunId = dfun_id, iBinds = binds, iPrags = uprags }] + checkValidTheta InstThetaCtxt theta `thenTc_` + checkValidInstHead tau `thenTc` \ (clas,inst_tys) -> + checkTc (checkInstFDs theta clas inst_tys) + (instTypeErr (pprClassPred clas inst_tys) msg) `thenTc_` + newDFunName clas inst_tys src_loc `thenNF_Tc` \ dfun_name -> + returnTc (Just (InstInfo { iDFunId = mkDictFunId dfun_name clas tyvars inst_tys theta, + iBinds = binds, iPrags = uprags })) where msg = parens (ptext SLIT("the instance types do not agree with the functional dependencies of the class")) \end{code} @@ -320,7 +320,7 @@ getGenericInstances class_decls if null gen_inst_info then returnTc [] else - getDOptsTc `thenTc` \ dflags -> + getDOptsTc `thenNF_Tc` \ dflags -> ioToTc (dumpIfSet_dyn dflags Opt_D_dump_deriv "Generic instances" (vcat (map pprInstInfo gen_inst_info))) `thenNF_Tc_` @@ -414,12 +414,10 @@ mkGenericInstance clas loc (hs_ty, binds) newDFunName clas [inst_ty] loc `thenNF_Tc` \ dfun_name -> let inst_theta = [mkClassPred clas [mkTyVarTy tv] | tv <- tyvars] - inst_tys = [inst_ty] - dfun_id = mkDictFunId dfun_name clas tyvars inst_tys inst_theta + dfun_id = mkDictFunId dfun_name clas tyvars [inst_ty] inst_theta in - returnTc (InstInfo { iDFunId = dfun_id, - iBinds = binds, iPrags = [] }) + returnTc (InstInfo { iDFunId = dfun_id, iBinds = binds, iPrags = [] }) \end{code} @@ -512,100 +510,88 @@ First comes the easy case of a non-local instance decl. \begin{code} -tcInstDecl2 :: InstInfo -> NF_TcM (LIE, TcMonoBinds) --- tcInstDecl2 is called *only* on InstInfos +tcInstDecl2 :: InstInfo -> TcM (LIE, TcMonoBinds) -tcInstDecl2 (InstInfo { iDFunId = dfun_id, - iBinds = monobinds, iPrags = uprags }) +tcInstDecl2 (NewTypeDerived { iDFunId = dfun_id }) + = tcInstType InstTv (idType dfun_id) `thenNF_Tc` \ (inst_tyvars', dfun_theta', inst_head') -> + newDicts InstanceDeclOrigin dfun_theta' `thenNF_Tc` \ rep_dicts -> + let + rep_dict_id = ASSERT( isSingleton rep_dicts ) + instToId (head rep_dicts) -- Derived newtypes have just one dict arg + + body = TyLam inst_tyvars' $ + DictLam [rep_dict_id] $ + (HsVar unsafeCoerceId `TyApp` [idType rep_dict_id, inst_head']) + `HsApp` + (HsVar rep_dict_id) + -- You might wonder why we have the 'coerce'. It's because the + -- type equality mechanism isn't clever enough; see comments with Type.eqType. + -- So Lint complains if we don't have this. + in + returnTc (emptyLIE, VarMonoBind dfun_id body) + +tcInstDecl2 (InstInfo { iDFunId = dfun_id, iBinds = monobinds, iPrags = uprags }) = -- Prime error recovery recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyMonoBinds)) $ tcAddSrcLoc (getSrcLoc dfun_id) $ tcAddErrCtxt (instDeclCtxt (toHsType (idType dfun_id))) $ - - -- Instantiate the instance decl with tc-style type variables let - (inst_tyvars, dfun_theta, clas, inst_tys) = tcSplitDFunTy (idType dfun_id) + inst_ty = idType dfun_id + (inst_tyvars, _) = tcSplitForAllTys inst_ty + -- The tyvars of the instance decl scope over the 'where' part + -- Those tyvars are inside the dfun_id's type, which is a bit + -- bizarre, but OK so long as you realise it! in - tcInstSigTyVars InstTv inst_tyvars `thenNF_Tc` \ inst_tyvars' -> - let - tenv = mkTopTyVarSubst inst_tyvars (mkTyVarTys inst_tyvars') - inst_tys' = map (substTy tenv) inst_tys - dfun_theta' = substTheta tenv dfun_theta - origin = InstanceDeclOrigin + -- Instantiate the instance decl with tc-style type variables + tcInstType InstTv inst_ty `thenNF_Tc` \ (inst_tyvars', dfun_theta', inst_head') -> + let + Just pred = tcSplitPredTy_maybe inst_head' + (clas, inst_tys') = getClassPredTys pred (class_tyvars, sc_theta, _, op_items) = classBigSig clas - sel_names = [idName sel_id | (sel_id, _) <- op_items] - -- Instantiate the super-class context with inst_tys - sc_theta' = substTheta (mkTopTyVarSubst class_tyvars inst_tys') sc_theta - - -- Find any definitions in monobinds that aren't from the class - bad_bndrs = collectMonoBinders monobinds `minusList` sel_names + sc_theta' = substTheta (mkTyVarSubst class_tyvars inst_tys') sc_theta + origin = InstanceDeclOrigin in - -- Check that all the method bindings come from this class - mapTc (addErrTc . badMethodErr clas) bad_bndrs `thenNF_Tc_` - -- Create dictionary Ids from the specified instance contexts. - newDicts origin sc_theta' `thenNF_Tc` \ sc_dicts -> - newDicts origin dfun_theta' `thenNF_Tc` \ dfun_arg_dicts -> - newDicts origin [mkClassPred clas inst_tys'] `thenNF_Tc` \ [this_dict] -> - - tcExtendTyVarEnvForMeths inst_tyvars inst_tyvars' ( - -- The type variable from the dict fun actually scope - -- over the bindings. They were gotten from - -- the original instance declaration - + newDicts origin sc_theta' `thenNF_Tc` \ sc_dicts -> + newDicts origin dfun_theta' `thenNF_Tc` \ dfun_arg_dicts -> + newDicts origin [pred] `thenNF_Tc` \ [this_dict] -> -- Default-method Ids may be mentioned in synthesised RHSs, -- but they'll already be in the environment. - mapAndUnzip3Tc (tcMethodBind clas origin inst_tyvars' inst_tys' - dfun_theta' - monobinds uprags True) - op_items - ) `thenTc` \ (method_binds_s, insts_needed_s, meth_insts) -> + -- Check that all the method bindings come from this class + mkMethodBinds clas inst_tys' op_items monobinds `thenTc` \ (meth_insts, meth_infos) -> + + let -- These insts are in scope; quite a few, eh? + avail_insts = [this_dict] ++ dfun_arg_dicts ++ + sc_dicts ++ meth_insts + + xtve = inst_tyvars `zip` inst_tyvars' + tc_meth = tcMethodBind xtve inst_tyvars' dfun_theta' avail_insts + in + mapAndUnzipTc tc_meth meth_infos `thenTc` \ (meth_binds_s, meth_lie_s) -> + + -- Figure out bindings for the superclass context + tcSuperClasses inst_tyvars' dfun_arg_dicts sc_dicts + `thenTc` \ (zonked_inst_tyvars, sc_binds_inner, sc_binds_outer) -> -- Deal with SPECIALISE instance pragmas by making them -- look like SPECIALISE pragmas for the dfun let - dfun_prags = [SpecSig (idName dfun_id) ty loc | SpecInstSig ty loc <- uprags] + spec_prags = [ SpecSig (idName dfun_id) ty loc + | SpecInstSig ty loc <- uprags] in + tcExtendGlobalValEnv [dfun_id] ( - tcSpecSigs dfun_prags + tcExtendTyVarEnv2 xtve $ + tcExtendLocalValEnv2 [(idName sel_id, tcSigPolyId sig) + | (sel_id, sig, _) <- meth_infos] $ + -- Map sel_id to the local method name we are using + tcSpecSigs spec_prags ) `thenTc` \ (prag_binds, prag_lie) -> - -- Check the overloading constraints of the methods and superclasses - let - -- These insts are in scope; quite a few, eh? - avail_insts = [this_dict] ++ - dfun_arg_dicts ++ - sc_dicts ++ - meth_insts - - methods_lie = plusLIEs insts_needed_s - in - - -- Simplify the constraints from methods - tcAddErrCtxt methodCtxt ( - tcSimplifyCheck - (ptext SLIT("instance declaration context")) - inst_tyvars' - avail_insts - methods_lie - ) `thenTc` \ (const_lie1, lie_binds1) -> - - -- Figure out bindings for the superclass context - tcAddErrCtxt superClassCtxt ( - tcSimplifyCheck - (ptext SLIT("instance declaration context")) - inst_tyvars' - dfun_arg_dicts -- NB! Don't include this_dict here, else the sc_dicts - -- get bound by just selecting from this_dict!! - (mkLIE sc_dicts) - ) `thenTc` \ (const_lie2, lie_binds2) -> - - checkSigTyVars inst_tyvars' emptyVarSet `thenNF_Tc` \ zonked_inst_tyvars -> - -- Create the result bindings let local_dfun_id = setIdLocalExported dfun_id @@ -633,8 +619,8 @@ tcInstDecl2 (InstInfo { iDFunId = dfun_id, -- emit an error message. This in turn means that we don't -- mention the constructor, which doesn't exist for CCallable, CReturnable -- Hardly beautiful, but only three extra lines. - HsApp (TyApp (HsVar eRROR_ID) [idType this_dict_id]) - (HsLit (HsString msg)) + HsApp (TyApp (HsVar rUNTIME_ERROR_ID) [idType this_dict_id]) + (HsLit (HsStringPrim (mkFastString (stringToUtf8 msg)))) | otherwise -- The common case = mkHsConApp dict_constr inst_tys' (map HsVar scs_and_meths) @@ -646,26 +632,102 @@ tcInstDecl2 (InstInfo { iDFunId = dfun_id, -- than needing to be repeated here. where - msg = _PK_ ("Compiler error: bad dictionary " ++ showSDoc (ppr clas)) - - dict_bind = VarMonoBind this_dict_id dict_rhs - method_binds = andMonoBindList method_binds_s - - main_bind - = AbsBinds - zonked_inst_tyvars - (map instToId dfun_arg_dicts) - [(inst_tyvars', local_dfun_id, this_dict_id)] - inlines - (lie_binds1 `AndMonoBinds` - lie_binds2 `AndMonoBinds` - method_binds `AndMonoBinds` - dict_bind) + msg = "Compiler error: bad dictionary " ++ showSDoc (ppr clas) + + dict_bind = VarMonoBind this_dict_id dict_rhs + meth_binds = andMonoBindList meth_binds_s + all_binds = sc_binds_inner `AndMonoBinds` meth_binds `AndMonoBinds` dict_bind + + main_bind = AbsBinds + zonked_inst_tyvars + (map instToId dfun_arg_dicts) + [(inst_tyvars', local_dfun_id, this_dict_id)] + inlines all_binds in - returnTc (const_lie1 `plusLIE` const_lie2 `plusLIE` prag_lie, - main_bind `AndMonoBinds` prag_binds) + returnTc (plusLIEs meth_lie_s `plusLIE` prag_lie, + main_bind `AndMonoBinds` prag_binds `AndMonoBinds` sc_binds_outer) +\end{code} + +Superclass loops +~~~~~~~~~~~~~~~~ +We have to be very, very careful when generating superclasses, lest we +accidentally build a loop. Here's an example: + + class S a + + class S a => C a where { opc :: a -> a } + class S b => D b where { opd :: b -> b } + + instance C Int where + opc = opd + + instance D Int where + opd = opc + +From (instance C Int) we get the constraint set {ds1:S Int, dd:D Int} +Simplifying, we may well get: + $dfCInt = :C ds1 (opd dd) + dd = $dfDInt + ds1 = $p1 dd +Notice that we spot that we can extract ds1 from dd. + +Alas! Alack! We can do the same for (instance D Int): + + $dfDInt = :D ds2 (opc dc) + dc = $dfCInt + ds2 = $p1 dc + +And now we've defined the superclass in terms of itself. + + +Solution: treat the superclass context separately, and simplify it +all the way down to nothing on its own. Don't toss any 'free' parts +out to be simplified together with other bits of context. +Hence the tcSimplifyTop below. + +At a more basic level, don't include this_dict in the context wrt +which we simplify sc_dicts, else sc_dicts get bound by just selecting +from this_dict!! + +\begin{code} +tcSuperClasses inst_tyvars' dfun_arg_dicts sc_dicts + = tcAddErrCtxt superClassCtxt $ + tcSimplifyCheck doc inst_tyvars' + dfun_arg_dicts + (mkLIE sc_dicts) `thenTc` \ (sc_lie, sc_binds1) -> + + -- It's possible that the superclass stuff might have done unification + checkSigTyVars inst_tyvars' `thenTc` \ zonked_inst_tyvars -> + + -- We must simplify this all the way down + -- lest we build superclass loops + -- See notes about superclass loops above + tcSimplifyTop sc_lie `thenTc` \ sc_binds2 -> + + returnTc (zonked_inst_tyvars, sc_binds1, sc_binds2) + + where + doc = ptext SLIT("instance declaration superclass context") \end{code} +\begin{code} +mkMethodBinds clas inst_tys' op_items monobinds + = -- Check that all the method bindings come from this class + mapTc (addErrTc . badMethodErr clas) bad_bndrs `thenNF_Tc_` + + -- Make the method bindings + mapAndUnzipTc mk_method_bind op_items + + where + mk_method_bind op_item = mkMethodBind InstanceDeclOrigin clas + inst_tys' monobinds op_item + + -- Find any definitions in monobinds that aren't from the class + sel_names = [idName sel_id | (sel_id, _) <- op_items] + bad_bndrs = collectMonoBinders monobinds `minusList` sel_names +\end{code} + + ------------------------------ Inlining dfuns unconditionally ------------------------------