X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=ghc%2Fcompiler%2Ftypecheck%2FInst.lhs;h=ccd8e434b832d5315bc0331034aa7aded3b9b8f5;hb=f53483a24f46fb3aa09052d8c00c0fc5d7d9dcca;hp=d0d44cfe907b7dde41bd2f727be7c43c672eaad0;hpb=373dd3e08a954f551b8fea7e342e7f056eff319a;p=ghc-hetmet.git diff --git a/ghc/compiler/typecheck/Inst.lhs b/ghc/compiler/typecheck/Inst.lhs index d0d44cf..ccd8e43 100644 --- a/ghc/compiler/typecheck/Inst.lhs +++ b/ghc/compiler/typecheck/Inst.lhs @@ -5,259 +5,140 @@ \begin{code} module Inst ( - LIE, emptyLIE, unitLIE, plusLIE, consLIE, zonkLIE, + LIE, emptyLIE, unitLIE, plusLIE, consLIE, plusLIEs, mkLIE, isEmptyLIE, lieToList, listToLIE, + showLIE, Inst, - pprInst, pprInsts, pprInstsInFull, tidyInst, tidyInsts, + pprInst, pprInsts, pprInstsInFull, tidyInsts, tidyMoreInsts, - newDictFromOld, newDicts, newClassDicts, newDictsAtLoc, - newMethod, newMethodWithGivenTy, newOverloadedLit, - newIPDict, instOverloadedFun, - instantiateFdClassTys, instFunDeps, instFunDepsOfTheta, - newFunDepFromDict, + newDictsFromOld, newDicts, cloneDict, + newMethod, newMethodFromName, newMethodWithGivenTy, + newMethodWith, newMethodAtLoc, + newOverloadedLit, newIPDict, + tcInstCall, tcInstDataCon, tcSyntaxName, - tyVarsOfInst, tyVarsOfInsts, tyVarsOfLIE, instLoc, getDictClassTys, - getDictPred_maybe, getMethodTheta_maybe, - getFunDeps, getFunDepsOfLIE, - getIPs, getIPsOfLIE, - getAllFunDeps, getAllFunDepsOfLIE, + tyVarsOfInst, tyVarsOfInsts, tyVarsOfLIE, + ipNamesOfInst, ipNamesOfInsts, fdPredsOfInst, fdPredsOfInsts, + instLoc, getDictClassTys, dictPred, lookupInst, lookupSimpleInst, LookupInstResult(..), - isDict, isClassDict, isMethod, - isTyVarDict, isStdClassTyVarDict, isMethodFor, notFunDep, + isDict, isClassDict, isMethod, + isLinearInst, linearInstType, isIPDict, isInheritableInst, + isTyVarDict, isStdClassTyVarDict, isMethodFor, instBindingRequired, instCanBeGeneralised, - zonkInst, zonkInsts, zonkFunDeps, zonkTvFunDeps, - instToId, instToIdBndr, ipToId, + zonkInst, zonkInsts, + instToId, instName, InstOrigin(..), InstLoc, pprInstLoc ) where #include "HsVersions.h" +import {-# SOURCE #-} TcExpr( tcExpr ) + import HsSyn ( HsLit(..), HsOverLit(..), HsExpr(..) ) -import RnHsSyn ( RenamedHsOverLit ) -import TcHsSyn ( TcExpr, TcId, +import TcHsSyn ( TcExpr, TcId, TcIdSet, TypecheckedHsExpr, mkHsTyApp, mkHsDictApp, mkHsConApp, zonkId ) -import TcMonad -import TcEnv ( TcIdSet, tcGetInstEnv, tcLookupGlobalId ) -import InstEnv ( InstLookupResult(..), lookupInstEnv ) -import TcType ( TcThetaType, - TcType, TcTauType, TcTyVarSet, - zonkTcTyVars, zonkTcType, zonkTcTypes, - zonkTcThetaType +import TcRnMonad +import TcEnv ( tcGetInstEnv, tcLookupId, tcLookupTyCon ) +import InstEnv ( InstLookupResult(..), lookupInstEnv ) +import TcMType ( zonkTcType, zonkTcTypes, zonkTcPredType, zapToType, + zonkTcThetaType, tcInstTyVar, tcInstType, tcInstTyVars + ) +import TcType ( Type, TcType, TcThetaType, TcTyVarSet, + SourceType(..), PredType, ThetaType, TyVarDetails(VanillaTv), + tcSplitForAllTys, tcSplitForAllTys, mkTyConApp, + tcSplitMethodTy, tcSplitPhiTy, mkGenTyConApp, + isIntTy,isFloatTy, isIntegerTy, isDoubleTy, + tcIsTyVarTy, mkPredTy, mkTyVarTy, mkTyVarTys, + tyVarsOfType, tyVarsOfTypes, tyVarsOfPred, tidyPred, + isClassPred, isTyVarClassPred, isLinearPred, predHasFDs, + getClassPredTys, getClassPredTys_maybe, mkPredName, + isInheritablePred, isIPPred, + tidyType, tidyTypes, tidyFreeTyVars, tcSplitSigmaTy ) import CoreFVs ( idFreeTyVars ) -import Class ( Class, FunDep ) -import FunDeps ( instantiateFdClassTys ) -import Id ( Id, idType, mkUserLocal, mkSysLocal ) +import Class ( Class ) +import DataCon ( DataCon,dataConSig ) +import Id ( Id, idName, idType, mkUserLocal, mkSysLocal, mkLocalId, setIdUnique ) import PrelInfo ( isStandardClass, isCcallishClass, isNoDictClass ) -import Name ( mkDictOcc, mkMethodOcc, mkIPOcc, getOccName, nameUnique ) -import PprType ( pprPred ) -import Type ( Type, PredType(..), - isTyVarTy, mkDictTy, mkPredTy, - splitForAllTys, splitSigmaTy, funArgTy, - splitMethodTy, splitRhoTy, classesOfPreds, - tyVarsOfType, tyVarsOfTypes, tyVarsOfPred, - tidyOpenType, tidyOpenTypes - ) -import Subst ( emptyInScopeSet, mkSubst, mkInScopeSet, - substTy, substClasses, mkTyVarSubst, mkTopTyVarSubst +import Name ( Name, mkMethodOcc, getOccName ) +import PprType ( pprPred, pprParendType ) +import Subst ( emptyInScopeSet, mkSubst, + substTy, substTyWith, substTheta, mkTyVarSubst, mkTopTyVarSubst ) import Literal ( inIntRange ) -import VarEnv ( TidyEnv, lookupSubstEnv, SubstResult(..) ) +import Var ( TyVar ) +import VarEnv ( TidyEnv, emptyTidyEnv, lookupSubstEnv, SubstResult(..) ) import VarSet ( elemVarSet, emptyVarSet, unionVarSet ) -import TysWiredIn ( isIntTy, - floatDataCon, isFloatTy, - doubleDataCon, isDoubleTy, - isIntegerTy, voidTy - ) -import PrelNames( Unique, hasKey, fromIntName, fromIntegerClassOpKey ) -import Maybe ( catMaybes ) -import Util ( thenCmp, zipWithEqual, mapAccumL ) -import Bag +import TysWiredIn ( floatDataCon, doubleDataCon ) +import PrelNames( fromIntegerName, fromRationalName, rationalTyConName ) +import Util ( equalLength ) +import BasicTypes( IPName(..), mapIPName, ipNameName ) +import UniqSupply( uniqsFromSupply ) import Outputable \end{code} -%************************************************************************ -%* * -\subsection[Inst-collections]{LIE: a collection of Insts} -%* * -%************************************************************************ - -\begin{code} -type LIE = Bag Inst - -isEmptyLIE = isEmptyBag -emptyLIE = emptyBag -unitLIE inst = unitBag inst -mkLIE insts = listToBag insts -plusLIE lie1 lie2 = lie1 `unionBags` lie2 -consLIE inst lie = inst `consBag` lie -plusLIEs lies = unionManyBags lies -lieToList = bagToList -listToLIE = listToBag - -zonkLIE :: LIE -> NF_TcM LIE -zonkLIE lie = mapBagNF_Tc zonkInst lie - -pprInsts :: [Inst] -> SDoc -pprInsts insts = parens (sep (punctuate comma (map pprInst insts))) - - -pprInstsInFull insts - = vcat (map go insts) - where - go inst = quotes (ppr inst) <+> pprInstLoc (instLoc inst) -\end{code} - -%************************************************************************ -%* * -\subsection[Inst-types]{@Inst@ types} -%* * -%************************************************************************ - -An @Inst@ is either a dictionary, an instance of an overloaded -literal, or an instance of an overloaded value. We call the latter a -``method'' even though it may not correspond to a class operation. -For example, we might have an instance of the @double@ function at -type Int, represented by - - Method 34 doubleId [Int] origin - -\begin{code} -data Inst - = Dict - Unique - TcPredType - InstLoc - - | Method - Unique - - TcId -- The overloaded function - -- This function will be a global, local, or ClassOpId; - -- inside instance decls (only) it can also be an InstId! - -- The id needn't be completely polymorphic. - -- You'll probably find its name (for documentation purposes) - -- inside the InstOrigin - - [TcType] -- The types to which its polymorphic tyvars - -- should be instantiated. - -- These types must saturate the Id's foralls. - - TcThetaType -- The (types of the) dictionaries to which the function - -- must be applied to get the method - - TcTauType -- The type of the method - - InstLoc - - -- INVARIANT: in (Method u f tys theta tau loc) - -- type of (f tys dicts(from theta)) = tau - - | LitInst - Unique - RenamedHsOverLit -- The literal from the occurrence site - TcType -- The type at which the literal is used - InstLoc - - | FunDep - Unique - Class -- the class from which this arises - [FunDep TcType] - InstLoc -\end{code} - -Ordering -~~~~~~~~ -@Insts@ are ordered by their class/type info, rather than by their -unique. This allows the context-reduction mechanism to use standard finite -maps to do their stuff. - -\begin{code} -instance Ord Inst where - compare = cmpInst - -instance Eq Inst where - (==) i1 i2 = case i1 `cmpInst` i2 of - EQ -> True - other -> False - -cmpInst (Dict _ pred1 _) (Dict _ pred2 _) = (pred1 `compare` pred2) -cmpInst (Dict _ _ _) other = LT - -cmpInst (Method _ _ _ _ _ _) (Dict _ _ _) = GT -cmpInst (Method _ id1 tys1 _ _ _) (Method _ id2 tys2 _ _ _) = (id1 `compare` id2) `thenCmp` (tys1 `compare` tys2) -cmpInst (Method _ _ _ _ _ _) other = LT - -cmpInst (LitInst _ lit1 ty1 _) (LitInst _ lit2 ty2 _) = (lit1 `compare` lit2) `thenCmp` (ty1 `compare` ty2) -cmpInst (LitInst _ _ _ _) (FunDep _ _ _ _) = LT -cmpInst (LitInst _ _ _ _) other = GT - -cmpInst (FunDep _ clas1 fds1 _) (FunDep _ clas2 fds2 _) = (clas1 `compare` clas2) `thenCmp` (fds1 `compare` fds2) -cmpInst (FunDep _ _ _ _) other = GT - --- and they can only have HsInt or HsFracs in them. -\end{code} - Selection ~~~~~~~~~ \begin{code} -instLoc (Dict u pred loc) = loc -instLoc (Method u _ _ _ _ loc) = loc -instLoc (LitInst u lit ty loc) = loc -instLoc (FunDep _ _ _ loc) = loc +instName :: Inst -> Name +instName inst = idName (instToId inst) -getDictPred_maybe (Dict _ p _) = Just p -getDictPred_maybe _ = Nothing +instToId :: Inst -> TcId +instToId (Dict id _ _) = id +instToId (Method id _ _ _ _ _) = id +instToId (LitInst id _ _ _) = id -getMethodTheta_maybe (Method _ _ _ theta _ _) = Just theta -getMethodTheta_maybe _ = Nothing +instLoc (Dict _ _ loc) = loc +instLoc (Method _ _ _ _ _ loc) = loc +instLoc (LitInst _ _ _ loc) = loc -getDictClassTys (Dict u (Class clas tys) _) = (clas, tys) +dictPred (Dict _ pred _ ) = pred +dictPred inst = pprPanic "dictPred" (ppr inst) -getFunDeps (FunDep _ clas fds _) = Just (clas, fds) -getFunDeps _ = Nothing +getDictClassTys (Dict _ pred _) = getClassPredTys pred -getFunDepsOfLIE lie = catMaybes (map getFunDeps (lieToList lie)) +-- fdPredsOfInst is used to get predicates that contain functional +-- dependencies; i.e. should participate in improvement +fdPredsOfInst (Dict _ pred _) | predHasFDs pred = [pred] + | otherwise = [] +fdPredsOfInst (Method _ _ _ theta _ _) = filter predHasFDs theta +fdPredsOfInst other = [] -getIPsOfPred (IParam n ty) = [(n, ty)] -getIPsOfPred _ = [] -getIPsOfTheta theta = concatMap getIPsOfPred theta +fdPredsOfInsts :: [Inst] -> [PredType] +fdPredsOfInsts insts = concatMap fdPredsOfInst insts -getIPs (Dict u (IParam n ty) loc) = [(n, ty)] -getIPs (Method u id _ theta t loc) = getIPsOfTheta theta -getIPs _ = [] +isInheritableInst (Dict _ pred _) = isInheritablePred pred +isInheritableInst (Method _ _ _ theta _ _) = all isInheritablePred theta +isInheritableInst other = True -getIPsOfLIE lie = concatMap getIPs (lieToList lie) -getAllFunDeps (FunDep _ clas fds _) = fds -getAllFunDeps inst = map (\(n,ty) -> ([], [ty])) (getIPs inst) +ipNamesOfInsts :: [Inst] -> [Name] +ipNamesOfInst :: Inst -> [Name] +-- Get the implicit parameters mentioned by these Insts +-- NB: ?x and %x get different Names +ipNamesOfInsts insts = [n | inst <- insts, n <- ipNamesOfInst inst] -getAllFunDepsOfLIE lie = concat (map getAllFunDeps (lieToList lie)) +ipNamesOfInst (Dict _ (IParam n _) _) = [ipNameName n] +ipNamesOfInst (Method _ _ _ theta _ _) = [ipNameName n | IParam n _ <- theta] +ipNamesOfInst other = [] tyVarsOfInst :: Inst -> TcTyVarSet +tyVarsOfInst (LitInst _ _ ty _) = tyVarsOfType ty tyVarsOfInst (Dict _ pred _) = tyVarsOfPred pred tyVarsOfInst (Method _ id tys _ _ _) = tyVarsOfTypes tys `unionVarSet` idFreeTyVars id -- The id might have free type variables; in the case of -- locally-overloaded class methods, for example -tyVarsOfInst (LitInst _ _ ty _) = tyVarsOfType ty -tyVarsOfInst (FunDep _ _ fds _) - = foldr unionVarSet emptyVarSet (map tyVarsOfFd fds) - where tyVarsOfFd (ts1, ts2) = - tyVarsOfTypes ts1 `unionVarSet` tyVarsOfTypes ts2 -tyVarsOfInsts insts - = foldr unionVarSet emptyVarSet (map tyVarsOfInst insts) -tyVarsOfLIE lie - = foldr unionVarSet emptyVarSet (map tyVarsOfInst insts) - where insts = lieToList lie +tyVarsOfInsts insts = foldr (unionVarSet . tyVarsOfInst) emptyVarSet insts +tyVarsOfLIE lie = tyVarsOfInsts (lieToList lie) \end{code} Predicates @@ -268,8 +149,16 @@ isDict (Dict _ _ _) = True isDict other = False isClassDict :: Inst -> Bool -isClassDict (Dict _ (Class _ _) _) = True -isClassDict other = False +isClassDict (Dict _ pred _) = isClassPred pred +isClassDict other = False + +isTyVarDict :: Inst -> Bool +isTyVarDict (Dict _ pred _) = isTyVarClassPred pred +isTyVarDict other = False + +isIPDict :: Inst -> Bool +isIPDict (Dict _ pred _) = isIPPred pred +isIPDict other = False isMethod :: Inst -> Bool isMethod (Method _ _ _ _ _ _) = True @@ -279,18 +168,21 @@ isMethodFor :: TcIdSet -> Inst -> Bool isMethodFor ids (Method uniq id tys _ _ loc) = id `elemVarSet` ids isMethodFor ids inst = False -isTyVarDict :: Inst -> Bool -isTyVarDict (Dict _ (Class _ tys) _) = all isTyVarTy tys -isTyVarDict other = False +isLinearInst :: Inst -> Bool +isLinearInst (Dict _ pred _) = isLinearPred pred +isLinearInst other = False + -- We never build Method Insts that have + -- linear implicit paramters in them. + -- Hence no need to look for Methods + -- See TcExpr.tcId + +linearInstType :: Inst -> TcType -- %x::t --> t +linearInstType (Dict _ (IParam _ ty) _) = ty -isStdClassTyVarDict (Dict _ (Class clas [ty]) _) - = isStandardClass clas && isTyVarTy ty -isStdClassTyVarDict other - = False -notFunDep :: Inst -> Bool -notFunDep (FunDep _ _ _ _) = False -notFunDep other = True +isStdClassTyVarDict (Dict _ pred _) = case getClassPredTys_maybe pred of + Just (clas, [ty]) -> isStandardClass clas && tcIsTyVarTy ty + other -> False \end{code} Two predicates which deal with the case where class constraints don't @@ -300,110 +192,170 @@ must be witnessed by an actual binding; the second tells whether an \begin{code} instBindingRequired :: Inst -> Bool -instBindingRequired (Dict _ (Class clas _) _) = not (isNoDictClass clas) -instBindingRequired (Dict _ (IParam _ _) _) = False -instBindingRequired other = True +instBindingRequired (Dict _ (ClassP clas _) _) = not (isNoDictClass clas) +instBindingRequired other = True instCanBeGeneralised :: Inst -> Bool -instCanBeGeneralised (Dict _ (Class clas _) _) = not (isCcallishClass clas) -instCanBeGeneralised other = True +instCanBeGeneralised (Dict _ (ClassP clas _) _) = not (isCcallishClass clas) +instCanBeGeneralised other = True \end{code} -Construction -~~~~~~~~~~~~ +%************************************************************************ +%* * +\subsection{Building dictionaries} +%* * +%************************************************************************ \begin{code} newDicts :: InstOrigin -> TcThetaType - -> NF_TcM (LIE, [TcId]) + -> TcM [Inst] newDicts orig theta - = tcGetInstLoc orig `thenNF_Tc` \ loc -> - newDictsAtLoc loc theta `thenNF_Tc` \ (dicts, ids) -> - returnNF_Tc (listToBag dicts, ids) + = getInstLoc orig `thenM` \ loc -> + newDictsAtLoc loc theta + +cloneDict :: Inst -> TcM Inst +cloneDict (Dict id ty loc) = newUnique `thenM` \ uniq -> + returnM (Dict (setIdUnique id uniq) ty loc) -newClassDicts :: InstOrigin - -> [(Class,[TcType])] - -> NF_TcM (LIE, [TcId]) -newClassDicts orig theta - = newDicts orig (map (uncurry Class) theta) +newDictsFromOld :: Inst -> TcThetaType -> TcM [Inst] +newDictsFromOld (Dict _ _ loc) theta = newDictsAtLoc loc theta -- Local function, similar to newDicts, -- but with slightly different interface newDictsAtLoc :: InstLoc -> TcThetaType - -> NF_TcM ([Inst], [TcId]) -newDictsAtLoc loc theta = - tcGetUniques (length theta) `thenNF_Tc` \ new_uniqs -> - let - mk_dict u pred = Dict u pred loc - dicts = zipWithEqual "newDictsAtLoc" mk_dict new_uniqs theta - in - returnNF_Tc (dicts, map instToId dicts) + -> TcM [Inst] +newDictsAtLoc inst_loc@(_,loc,_) theta + = newUniqueSupply `thenM` \ us -> + returnM (zipWith mk_dict (uniqsFromSupply us) theta) + where + mk_dict uniq pred = Dict (mkLocalId (mkPredName uniq loc pred) (mkPredTy pred)) pred inst_loc + +-- For vanilla implicit parameters, there is only one in scope +-- at any time, so we used to use the name of the implicit parameter itself +-- But with splittable implicit parameters there may be many in +-- scope, so we make up a new name. +newIPDict :: InstOrigin -> IPName Name -> Type + -> TcM (IPName Id, Inst) +newIPDict orig ip_name ty + = getInstLoc orig `thenM` \ inst_loc@(_,loc,_) -> + newUnique `thenM` \ uniq -> + let + pred = IParam ip_name ty + id = mkLocalId (mkPredName uniq loc pred) (mkPredTy pred) + in + returnM (mapIPName (\n -> id) ip_name, Dict id pred inst_loc) +\end{code} + + + +%************************************************************************ +%* * +\subsection{Building methods (calls of overloaded functions)} +%* * +%************************************************************************ + + +\begin{code} +tcInstCall :: InstOrigin -> TcType -> TcM (TypecheckedHsExpr -> TypecheckedHsExpr, TcType) +tcInstCall orig fun_ty -- fun_ty is usually a sigma-type + = tcInstType VanillaTv fun_ty `thenM` \ (tyvars, theta, tau) -> + newDicts orig theta `thenM` \ dicts -> + extendLIEs dicts `thenM_` + let + inst_fn e = mkHsDictApp (mkHsTyApp e (mkTyVarTys tyvars)) (map instToId dicts) + in + returnM (inst_fn, tau) + +tcInstDataCon :: InstOrigin -> DataCon + -> TcM ([TcType], -- Types to instantiate at + [Inst], -- Existential dictionaries to apply to + [TcType], -- Argument types of constructor + TcType, -- Result type + [TyVar]) -- Existential tyvars +tcInstDataCon orig data_con + = let + (tvs, stupid_theta, ex_tvs, ex_theta, arg_tys, tycon) = dataConSig data_con + -- We generate constraints for the stupid theta even when + -- pattern matching (as the Report requires) + in + tcInstTyVars VanillaTv (tvs ++ ex_tvs) `thenM` \ (all_tvs', ty_args', tenv) -> + let + stupid_theta' = substTheta tenv stupid_theta + ex_theta' = substTheta tenv ex_theta + arg_tys' = map (substTy tenv) arg_tys + + n_normal_tvs = length tvs + ex_tvs' = drop n_normal_tvs all_tvs' + result_ty = mkTyConApp tycon (take n_normal_tvs ty_args') + in + newDicts orig stupid_theta' `thenM` \ stupid_dicts -> + newDicts orig ex_theta' `thenM` \ ex_dicts -> + + -- Note that we return the stupid theta *only* in the LIE; + -- we don't otherwise use it at all + extendLIEs stupid_dicts `thenM_` -newDictFromOld :: Inst -> Class -> [TcType] -> NF_TcM Inst -newDictFromOld (Dict _ _ loc) clas tys - = tcGetUnique `thenNF_Tc` \ uniq -> - returnNF_Tc (Dict uniq (Class clas tys) loc) + returnM (ty_args', ex_dicts, arg_tys', result_ty, ex_tvs') +newMethodFromName :: InstOrigin -> TcType -> Name -> TcM TcId +newMethodFromName origin ty name + = tcLookupId name `thenM` \ id -> + -- Use tcLookupId not tcLookupGlobalId; the method is almost + -- always a class op, but with -fno-implicit-prelude GHC is + -- meant to find whatever thing is in scope, and that may + -- be an ordinary function. + newMethod origin id [ty] + newMethod :: InstOrigin -> TcId -> [TcType] - -> NF_TcM (LIE, TcId) + -> TcM Id newMethod orig id tys = -- Get the Id type and instantiate it at the specified types let - (tyvars, rho) = splitForAllTys (idType id) - rho_ty = substTy (mkTyVarSubst tyvars tys) rho - (pred, tau) = splitMethodTy rho_ty + (tyvars, rho) = tcSplitForAllTys (idType id) + rho_ty = substTyWith tyvars tys rho + (pred, tau) = tcSplitMethodTy rho_ty in - newMethodWithGivenTy orig id tys [pred] tau `thenNF_Tc` \ meth_inst -> - returnNF_Tc (unitLIE meth_inst, instToId meth_inst) - -instOverloadedFun orig v arg_tys theta tau --- This is where we introduce new functional dependencies into the LIE - = newMethodWithGivenTy orig v arg_tys theta tau `thenNF_Tc` \ inst -> - instFunDeps orig theta `thenNF_Tc` \ fds -> - returnNF_Tc (instToId inst, mkLIE (inst : fds)) - -instFunDeps orig theta - = tcGetUnique `thenNF_Tc` \ uniq -> - tcGetInstLoc orig `thenNF_Tc` \ loc -> - let ifd (Class clas tys) = - let fds = instantiateFdClassTys clas tys in - if null fds then Nothing else Just (FunDep uniq clas fds loc) - ifd _ = Nothing - in returnNF_Tc (catMaybes (map ifd theta)) - -instFunDepsOfTheta theta - = let ifd (Class clas tys) = instantiateFdClassTys clas tys - ifd (IParam n ty) = [([], [ty])] - in concat (map ifd theta) + newMethodWithGivenTy orig id tys [pred] tau newMethodWithGivenTy orig id tys theta tau - = tcGetInstLoc orig `thenNF_Tc` \ loc -> - newMethodWith id tys theta tau loc - -newMethodWith id tys theta tau loc - = tcGetUnique `thenNF_Tc` \ new_uniq -> - returnNF_Tc (Method new_uniq id tys theta tau loc) + = getInstLoc orig `thenM` \ loc -> + newMethodWith loc id tys theta tau `thenM` \ inst -> + extendLIE inst `thenM_` + returnM (instToId inst) + +-------------------------------------------- +-- newMethodWith and newMethodAtLoc do *not* drop the +-- Inst into the LIE; they just returns the Inst +-- This is important because they are used by TcSimplify +-- to simplify Insts + +newMethodWith inst_loc@(_,loc,_) id tys theta tau + = newUnique `thenM` \ new_uniq -> + let + meth_id = mkUserLocal (mkMethodOcc (getOccName id)) new_uniq tau loc + inst = Method meth_id id tys theta tau inst_loc + in + returnM inst newMethodAtLoc :: InstLoc -> Id -> [TcType] - -> NF_TcM (Inst, TcId) -newMethodAtLoc loc real_id tys -- Local function, similar to newMethod but with - -- slightly different interface + -> TcM Inst +newMethodAtLoc inst_loc real_id tys + -- This actually builds the Inst = -- Get the Id type and instantiate it at the specified types - tcGetUnique `thenNF_Tc` \ new_uniq -> let - (tyvars,rho) = splitForAllTys (idType real_id) - rho_ty = ASSERT( length tyvars == length tys ) + (tyvars,rho) = tcSplitForAllTys (idType real_id) + rho_ty = ASSERT( equalLength tyvars tys ) substTy (mkTopTyVarSubst tyvars tys) rho - (theta, tau) = splitRhoTy rho_ty - meth_inst = Method new_uniq real_id tys theta tau loc + (theta, tau) = tcSplitPhiTy rho_ty in - returnNF_Tc (meth_inst, instToId meth_inst) + newMethodWith inst_loc real_id tys theta tau \end{code} In newOverloadedLit we convert directly to an Int or Integer if we @@ -413,132 +365,114 @@ cases (the rest are caught in lookupInst). \begin{code} newOverloadedLit :: InstOrigin - -> RenamedHsOverLit + -> HsOverLit -> TcType - -> NF_TcM (TcExpr, LIE) -newOverloadedLit orig (HsIntegral i _) ty - | isIntTy ty && inIntRange i -- Short cut for Int - = returnNF_Tc (int_lit, emptyLIE) + -> TcM TcExpr +newOverloadedLit orig lit@(HsIntegral i fi) expected_ty + | fi /= fromIntegerName -- Do not generate a LitInst for rebindable + -- syntax. Reason: tcSyntaxName does unification + -- which is very inconvenient in tcSimplify + = tcSyntaxName orig expected_ty fromIntegerName fi `thenM` \ (expr, _) -> + returnM (HsApp expr (HsLit (HsInteger i))) - | isIntegerTy ty -- Short cut for Integer - = returnNF_Tc (integer_lit, emptyLIE) + | Just expr <- shortCutIntLit i expected_ty + = returnM expr - where - int_lit = HsLit (HsInt i) - integer_lit = HsLit (HsInteger i) + | otherwise + = newLitInst orig lit expected_ty + +newOverloadedLit orig lit@(HsFractional r fr) expected_ty + | fr /= fromRationalName -- c.f. HsIntegral case + = tcSyntaxName orig expected_ty fromRationalName fr `thenM` \ (expr, _) -> + mkRatLit r `thenM` \ rat_lit -> + returnM (HsApp expr rat_lit) + + | Just expr <- shortCutFracLit r expected_ty + = returnM expr -newOverloadedLit orig lit ty -- The general case - = tcGetInstLoc orig `thenNF_Tc` \ loc -> - tcGetUnique `thenNF_Tc` \ new_uniq -> + | otherwise + = newLitInst orig lit expected_ty + +newLitInst orig lit expected_ty + = getInstLoc orig `thenM` \ loc -> + newUnique `thenM` \ new_uniq -> + zapToType expected_ty `thenM_` + -- The expected type might be a 'hole' type variable, + -- in which case we must zap it to an ordinary type variable let - lit_inst = LitInst new_uniq lit ty loc + lit_inst = LitInst lit_id lit expected_ty loc + lit_id = mkSysLocal FSLIT("lit") new_uniq expected_ty in - returnNF_Tc (HsVar (instToId lit_inst), unitLIE lit_inst) -\end{code} - -\begin{code} -newFunDepFromDict dict - | isClassDict dict - = tcGetUnique `thenNF_Tc` \ uniq -> - let (clas, tys) = getDictClassTys dict - fds = instantiateFdClassTys clas tys - inst = FunDep uniq clas fds (instLoc dict) + extendLIE lit_inst `thenM_` + returnM (HsVar (instToId lit_inst)) + +shortCutIntLit :: Integer -> TcType -> Maybe TcExpr +shortCutIntLit i ty + | isIntTy ty && inIntRange i -- Short cut for Int + = Just (HsLit (HsInt i)) + | isIntegerTy ty -- Short cut for Integer + = Just (HsLit (HsInteger i)) + | otherwise = Nothing + +shortCutFracLit :: Rational -> TcType -> Maybe TcExpr +shortCutFracLit f ty + | isFloatTy ty + = Just (mkHsConApp floatDataCon [] [HsLit (HsFloatPrim f)]) + | isDoubleTy ty + = Just (mkHsConApp doubleDataCon [] [HsLit (HsDoublePrim f)]) + | otherwise = Nothing + +mkRatLit :: Rational -> TcM TcExpr +mkRatLit r + = tcLookupTyCon rationalTyConName `thenM` \ rat_tc -> + let + rational_ty = mkGenTyConApp rat_tc [] in - if null fds then returnNF_Tc Nothing else returnNF_Tc (Just inst) - | otherwise - = returnNF_Tc Nothing + returnM (HsLit (HsRat r rational_ty)) \end{code} -\begin{code} -newIPDict name ty loc - = tcGetUnique `thenNF_Tc` \ new_uniq -> - let d = Dict new_uniq (IParam name ty) loc in - returnNF_Tc d -\end{code} - -\begin{code} -instToId :: Inst -> TcId -instToId inst = instToIdBndr inst - -instToIdBndr :: Inst -> TcId -instToIdBndr (Dict u (Class clas tys) (_,loc,_)) - = mkUserLocal (mkDictOcc (getOccName clas)) u (mkDictTy clas tys) loc -instToIdBndr (Dict u (IParam n ty) (_,loc,_)) - = ipToId n ty loc - -instToIdBndr (Method u id tys theta tau (_,loc,_)) - = mkUserLocal (mkMethodOcc (getOccName id)) u tau loc - -instToIdBndr (LitInst u list ty loc) - = mkSysLocal SLIT("lit") u ty - -instToIdBndr (FunDep u clas fds _) - = mkSysLocal SLIT("FunDep") u voidTy - -ipToId n ty loc - = mkUserLocal (mkIPOcc (getOccName n)) (nameUnique n) (mkPredTy (IParam n ty)) loc -\end{code} +%************************************************************************ +%* * +\subsection{Zonking} +%* * +%************************************************************************ -Zonking -~~~~~~~ Zonking makes sure that the instance types are fully zonked, -but doesn't do the same for the Id in a Method. There's no +but doesn't do the same for any of the Ids in an Inst. There's no need, and it's a lot of extra work. \begin{code} -zonkPred :: TcPredType -> NF_TcM TcPredType -zonkPred (Class clas tys) - = zonkTcTypes tys `thenNF_Tc` \ new_tys -> - returnNF_Tc (Class clas new_tys) -zonkPred (IParam n ty) - = zonkTcType ty `thenNF_Tc` \ new_ty -> - returnNF_Tc (IParam n new_ty) - -zonkInst :: Inst -> NF_TcM Inst -zonkInst (Dict u pred loc) - = zonkPred pred `thenNF_Tc` \ new_pred -> - returnNF_Tc (Dict u new_pred loc) - -zonkInst (Method u id tys theta tau loc) - = zonkId id `thenNF_Tc` \ new_id -> +zonkInst :: Inst -> TcM Inst +zonkInst (Dict id pred loc) + = zonkTcPredType pred `thenM` \ new_pred -> + returnM (Dict id new_pred loc) + +zonkInst (Method m id tys theta tau loc) + = zonkId id `thenM` \ new_id -> -- Essential to zonk the id in case it's a local variable -- Can't use zonkIdOcc because the id might itself be -- an InstId, in which case it won't be in scope - zonkTcTypes tys `thenNF_Tc` \ new_tys -> - zonkTcThetaType theta `thenNF_Tc` \ new_theta -> - zonkTcType tau `thenNF_Tc` \ new_tau -> - returnNF_Tc (Method u new_id new_tys new_theta new_tau loc) - -zonkInst (LitInst u lit ty loc) - = zonkTcType ty `thenNF_Tc` \ new_ty -> - returnNF_Tc (LitInst u lit new_ty loc) + zonkTcTypes tys `thenM` \ new_tys -> + zonkTcThetaType theta `thenM` \ new_theta -> + zonkTcType tau `thenM` \ new_tau -> + returnM (Method m new_id new_tys new_theta new_tau loc) -zonkInst (FunDep u clas fds loc) - = zonkFunDeps fds `thenNF_Tc` \ fds' -> - returnNF_Tc (FunDep u clas fds' loc) +zonkInst (LitInst id lit ty loc) + = zonkTcType ty `thenM` \ new_ty -> + returnM (LitInst id lit new_ty loc) -zonkInsts insts = mapNF_Tc zonkInst insts - -zonkFunDeps fds = mapNF_Tc zonkFd fds - where - zonkFd (ts1, ts2) - = zonkTcTypes ts1 `thenNF_Tc` \ ts1' -> - zonkTcTypes ts2 `thenNF_Tc` \ ts2' -> - returnNF_Tc (ts1', ts2') - -zonkTvFunDeps fds = mapNF_Tc zonkFd fds - where - zonkFd (tvs1, tvs2) - = zonkTcTyVars tvs1 `thenNF_Tc` \ tvs1' -> - zonkTcTyVars tvs2 `thenNF_Tc` \ tvs2' -> - returnNF_Tc (tvs1', tvs2') +zonkInsts insts = mappM zonkInst insts \end{code} -Printing -~~~~~~~~ +%************************************************************************ +%* * +\subsection{Printing} +%* * +%************************************************************************ + ToDo: improve these pretty-printing things. The ``origin'' is really only relevant in error messages. @@ -546,6 +480,14 @@ relevant in error messages. instance Outputable Inst where ppr inst = pprInst inst +pprInsts :: [Inst] -> SDoc +pprInsts insts = parens (sep (punctuate comma (map pprInst insts))) + +pprInstsInFull insts + = vcat (map go insts) + where + go inst = quotes (ppr inst) <+> pprInstLoc (instLoc inst) + pprInst (LitInst u lit ty loc) = hsep [ppr lit, ptext SLIT("at"), ppr ty, show_uniq u] @@ -553,55 +495,41 @@ pprInst (Dict u pred loc) = pprPred pred <+> show_uniq u pprInst m@(Method u id tys theta tau loc) = hsep [ppr id, ptext SLIT("at"), - brackets (interppSP tys) {- , + brackets (sep (map pprParendType tys)) {- , ptext SLIT("theta"), ppr theta, ptext SLIT("tau"), ppr tau show_uniq u, ppr (instToId m) -}] -pprInst (FunDep _ clas fds loc) - = hsep [ppr clas, ppr fds] - -tidyPred :: TidyEnv -> TcPredType -> (TidyEnv, TcPredType) -tidyPred env (Class clas tys) - = (env', Class clas tys') - where - (env', tys') = tidyOpenTypes env tys -tidyPred env (IParam n ty) - = (env', IParam n ty') - where - (env', ty') = tidyOpenType env ty - -tidyInst :: TidyEnv -> Inst -> (TidyEnv, Inst) -tidyInst env (LitInst u lit ty loc) - = (env', LitInst u lit ty' loc) - where - (env', ty') = tidyOpenType env ty +show_uniq u = ifPprDebug (text "{-" <> ppr u <> text "-}") -tidyInst env (Dict u pred loc) - = (env', Dict u pred' loc) - where - (env', pred') = tidyPred env pred +tidyInst :: TidyEnv -> Inst -> Inst +tidyInst env (LitInst u lit ty loc) = LitInst u lit (tidyType env ty) loc +tidyInst env (Dict u pred loc) = Dict u (tidyPred env pred) loc +tidyInst env (Method u id tys theta tau loc) = Method u id (tidyTypes env tys) theta tau loc -tidyInst env (Method u id tys theta tau loc) - = (env', Method u id tys' theta tau loc) - -- Leave theta, tau alone cos we don't print them +tidyMoreInsts :: TidyEnv -> [Inst] -> (TidyEnv, [Inst]) +-- This function doesn't assume that the tyvars are in scope +-- so it works like tidyOpenType, returning a TidyEnv +tidyMoreInsts env insts + = (env', map (tidyInst env') insts) where - (env', tys') = tidyOpenTypes env tys - --- this case shouldn't arise... (we never print fundeps) -tidyInst env fd@(FunDep _ clas fds loc) - = (env, fd) + env' = tidyFreeTyVars env (tyVarsOfInsts insts) -tidyInsts env insts = mapAccumL tidyInst env insts +tidyInsts :: [Inst] -> (TidyEnv, [Inst]) +tidyInsts insts = tidyMoreInsts emptyTidyEnv insts -show_uniq u = ifPprDebug (text "{-" <> ppr u <> text "-}") +showLIE :: String -> TcM () -- Debugging +showLIE str + = do { lie_var <- getLIEVar ; + lie <- readMutVar lie_var ; + traceTc (text str <+> pprInstsInFull (lieToList lie)) } \end{code} %************************************************************************ %* * -\subsection[InstEnv-types]{Type declarations} +\subsection{Looking up Insts} %* * %************************************************************************ @@ -611,100 +539,87 @@ data LookupInstResult s | SimpleInst TcExpr -- Just a variable, type application, or literal | GenInst [Inst] TcExpr -- The expression and its needed insts -lookupInst :: Inst - -> NF_TcM (LookupInstResult s) +lookupInst :: Inst -> TcM (LookupInstResult s) +-- It's important that lookupInst does not put any new stuff into +-- the LIE. Instead, any Insts needed by the lookup are returned in +-- the LookupInstResult, where they can be further processed by tcSimplify --- Dictionaries -lookupInst dict@(Dict _ (Class clas tys) loc) - = tcGetInstEnv `thenNF_Tc` \ inst_env -> - case lookupInstEnv inst_env clas tys of +-- Dictionaries +lookupInst dict@(Dict _ (ClassP clas tys) loc) + = getDOpts `thenM` \ dflags -> + tcGetInstEnv `thenM` \ inst_env -> + case lookupInstEnv dflags inst_env clas tys of FoundInst tenv dfun_id - -> let - subst = mkSubst (mkInScopeSet (tyVarsOfTypes tys)) tenv - (tyvars, rho) = splitForAllTys (idType dfun_id) - ty_args = map subst_tv tyvars - dfun_rho = substTy subst rho - (theta, _) = splitRhoTy dfun_rho - ty_app = mkHsTyApp (HsVar dfun_id) ty_args - subst_tv tv = case lookupSubstEnv tenv tv of - Just (DoneTy ty) -> ty - -- tenv should bind all the tyvars + -> -- It's possible that not all the tyvars are in + -- the substitution, tenv. For example: + -- instance C X a => D X where ... + -- (presumably there's a functional dependency in class C) + -- Hence the mk_ty_arg to instantiate any un-substituted tyvars. + let + (tyvars, rho) = tcSplitForAllTys (idType dfun_id) + mk_ty_arg tv = case lookupSubstEnv tenv tv of + Just (DoneTy ty) -> returnM ty + Nothing -> tcInstTyVar VanillaTv tv `thenM` \ tc_tv -> + returnM (mkTyVarTy tc_tv) + in + mappM mk_ty_arg tyvars `thenM` \ ty_args -> + let + dfun_rho = substTy (mkTyVarSubst tyvars ty_args) rho + (theta, _) = tcSplitPhiTy dfun_rho + ty_app = mkHsTyApp (HsVar dfun_id) ty_args in if null theta then - returnNF_Tc (SimpleInst ty_app) + returnM (SimpleInst ty_app) else - newDictsAtLoc loc theta `thenNF_Tc` \ (dicts, dict_ids) -> + newDictsAtLoc loc theta `thenM` \ dicts -> let - rhs = mkHsDictApp ty_app dict_ids + rhs = mkHsDictApp ty_app (map instToId dicts) in - returnNF_Tc (GenInst dicts rhs) + returnM (GenInst dicts rhs) + + other -> returnM NoInstance - other -> returnNF_Tc NoInstance -lookupInst dict@(Dict _ _ loc) = returnNF_Tc NoInstance +lookupInst (Dict _ _ _) = returnM NoInstance -- Methods lookupInst inst@(Method _ id tys theta _ loc) - = newDictsAtLoc loc theta `thenNF_Tc` \ (dicts, dict_ids) -> - returnNF_Tc (GenInst dicts (mkHsDictApp (mkHsTyApp (HsVar id) tys) dict_ids)) + = newDictsAtLoc loc theta `thenM` \ dicts -> + returnM (GenInst dicts (mkHsDictApp (mkHsTyApp (HsVar id) tys) (map instToId dicts))) -- Literals -lookupInst inst@(LitInst u (HsIntegral i from_integer_name) ty loc) - | isIntTy ty && in_int_range -- Short cut for Int - = returnNF_Tc (GenInst [] int_lit) - -- GenInst, not SimpleInst, because int_lit is actually a constructor application - - | isIntegerTy ty -- Short cut for Integer - = returnNF_Tc (GenInst [] integer_lit) - - | in_int_range -- It's overloaded but small enough to fit into an Int - && from_integer_name `hasKey` fromIntegerClassOpKey -- And it's the built-in prelude fromInteger - -- (i.e. no funny business with user-defined - -- packages of numeric classes) - = -- So we can use the Prelude fromInt - tcLookupGlobalId fromIntName `thenNF_Tc` \ from_int -> - newMethodAtLoc loc from_int [ty] `thenNF_Tc` \ (method_inst, method_id) -> - returnNF_Tc (GenInst [method_inst] (HsApp (HsVar method_id) int_lit)) - - | otherwise -- Alas, it is overloaded and a big literal! - = tcLookupGlobalId from_integer_name `thenNF_Tc` \ from_integer -> - newMethodAtLoc loc from_integer [ty] `thenNF_Tc` \ (method_inst, method_id) -> - returnNF_Tc (GenInst [method_inst] (HsApp (HsVar method_id) integer_lit)) - where - in_int_range = inIntRange i - integer_lit = HsLit (HsInteger i) - int_lit = HsLit (HsInt i) - --- similar idea for overloaded floating point literals: if the literal is --- *definitely* a float or a double, generate the real thing here. +-- Look for short cuts first: if the literal is *definitely* a +-- int, integer, float or a double, generate the real thing here. -- This is essential (see nofib/spectral/nucleic). +-- [Same shortcut as in newOverloadedLit, but we +-- may have done some unification by now] -lookupInst inst@(LitInst u (HsFractional f from_rat_name) ty loc) - | isFloatTy ty = returnNF_Tc (GenInst [] float_lit) - | isDoubleTy ty = returnNF_Tc (GenInst [] double_lit) - | otherwise - = tcLookupGlobalId from_rat_name `thenNF_Tc` \ from_rational -> - newMethodAtLoc loc from_rational [ty] `thenNF_Tc` \ (method_inst, method_id) -> - let - rational_ty = funArgTy (idType method_id) - rational_lit = HsLit (HsRat f rational_ty) - in - returnNF_Tc (GenInst [method_inst] (HsApp (HsVar method_id) rational_lit)) - - where - floatprim_lit = HsLit (HsFloatPrim f) - float_lit = mkHsConApp floatDataCon [] [floatprim_lit] - doubleprim_lit = HsLit (HsDoublePrim f) - double_lit = mkHsConApp doubleDataCon [] [doubleprim_lit] +lookupInst inst@(LitInst u (HsIntegral i from_integer_name) ty loc) + | Just expr <- shortCutIntLit i ty + = returnM (GenInst [] expr) -- GenInst, not SimpleInst, because + -- expr may be a constructor application + | otherwise + = ASSERT( from_integer_name == fromIntegerName ) -- A LitInst invariant + tcLookupId fromIntegerName `thenM` \ from_integer -> + newMethodAtLoc loc from_integer [ty] `thenM` \ method_inst -> + returnM (GenInst [method_inst] + (HsApp (HsVar (instToId method_inst)) (HsLit (HsInteger i)))) --- there are no `instances' of functional dependencies or implicit params -lookupInst _ = returnNF_Tc NoInstance +lookupInst inst@(LitInst u (HsFractional f from_rat_name) ty loc) + | Just expr <- shortCutFracLit f ty + = returnM (GenInst [] expr) + | otherwise + = ASSERT( from_rat_name == fromRationalName ) -- A LitInst invariant + tcLookupId fromRationalName `thenM` \ from_rational -> + newMethodAtLoc loc from_rational [ty] `thenM` \ method_inst -> + mkRatLit f `thenM` \ rat_lit -> + returnM (GenInst [method_inst] (HsApp (HsVar (instToId method_inst)) rat_lit)) \end{code} There is a second, simpler interface, when you want an instance of a @@ -714,19 +629,84 @@ ambiguous dictionaries. \begin{code} lookupSimpleInst :: Class - -> [Type] -- Look up (c,t) - -> NF_TcM (Maybe [(Class,[Type])]) -- Here are the needed (c,t)s + -> [Type] -- Look up (c,t) + -> TcM (Maybe ThetaType) -- Here are the needed (c,t)s lookupSimpleInst clas tys - = tcGetInstEnv `thenNF_Tc` \ inst_env -> - case lookupInstEnv inst_env clas tys of + = getDOpts `thenM` \ dflags -> + tcGetInstEnv `thenM` \ inst_env -> + case lookupInstEnv dflags inst_env clas tys of FoundInst tenv dfun - -> returnNF_Tc (Just (substClasses (mkSubst emptyInScopeSet tenv) theta')) + -> returnM (Just (substTheta (mkSubst emptyInScopeSet tenv) theta)) where - (_, theta, _) = splitSigmaTy (idType dfun) - theta' = classesOfPreds theta + (_, rho) = tcSplitForAllTys (idType dfun) + (theta,_) = tcSplitPhiTy rho - other -> returnNF_Tc Nothing + other -> returnM Nothing \end{code} +%************************************************************************ +%* * + Re-mappable syntax +%* * +%************************************************************************ + + +Suppose we are doing the -fno-implicit-prelude thing, and we encounter +a do-expression. We have to find (>>) in the current environment, which is +done by the rename. Then we have to check that it has the same type as +Control.Monad.(>>). Or, more precisely, a compatible type. One 'customer' had +this: + + (>>) :: HB m n mn => m a -> n b -> mn b + +So the idea is to generate a local binding for (>>), thus: + + let then72 :: forall a b. m a -> m b -> m b + then72 = ...something involving the user's (>>)... + in + ...the do-expression... + +Now the do-expression can proceed using then72, which has exactly +the expected type. + +In fact tcSyntaxName just generates the RHS for then72, because we only +want an actual binding in the do-expression case. For literals, we can +just use the expression inline. + +\begin{code} +tcSyntaxName :: InstOrigin + -> TcType -- Type to instantiate it at + -> Name -> Name -- (Standard name, user name) + -> TcM (TcExpr, TcType) -- Suitable expression with its type + +-- NB: tcSyntaxName calls tcExpr, and hence can do unification. +-- So we do not call it from lookupInst, which is called from tcSimplify + +tcSyntaxName orig ty std_nm user_nm + | std_nm == user_nm + = newMethodFromName orig ty std_nm `thenM` \ id -> + returnM (HsVar id, idType id) + + | otherwise + = tcLookupId std_nm `thenM` \ std_id -> + let + -- C.f. newMethodAtLoc + ([tv], _, tau) = tcSplitSigmaTy (idType std_id) + tau1 = substTy (mkTopTyVarSubst [tv] [ty]) tau + in + addErrCtxtM (syntaxNameCtxt user_nm orig tau1) $ + tcExpr (HsVar user_nm) tau1 `thenM` \ user_fn -> + returnM (user_fn, tau1) + +syntaxNameCtxt name orig ty tidy_env + = getInstLoc orig `thenM` \ inst_loc -> + let + msg = vcat [ptext SLIT("When checking that") <+> quotes (ppr name) <+> + ptext SLIT("(needed by a syntactic construct)"), + nest 2 (ptext SLIT("has the required type:") <+> ppr (tidyType tidy_env ty)), + nest 2 (pprInstLoc inst_loc)] + in + returnM (tidy_env, msg) +\end{code}