X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=ghc%2Fcompiler%2Ftypecheck%2FInst.lhs;h=8768e202505aacb50fb35ec6a0f8ff06cffdbadb;hb=ac10f8408520a30e8437496d320b8b86afda2e8f;hp=ed0e6656a4320673db530102a132fadc5fa66ca7;hpb=aaed11810cfb0f8890376142740e731cdf84c001;p=ghc-hetmet.git diff --git a/ghc/compiler/typecheck/Inst.lhs b/ghc/compiler/typecheck/Inst.lhs index ed0e665..8768e20 100644 --- a/ghc/compiler/typecheck/Inst.lhs +++ b/ghc/compiler/typecheck/Inst.lhs @@ -5,190 +5,92 @@ \begin{code} module Inst ( - LIE, emptyLIE, unitLIE, plusLIE, consLIE, zonkLIE, - plusLIEs, mkLIE, isEmptyLIE, lieToList, listToLIE, - Inst, - pprInst, pprInsts, pprInstsInFull, tidyInsts, tidyMoreInsts, - newDictsFromOld, newDicts, cloneDict, - newMethod, newMethodWithGivenTy, newMethodAtLoc, - newOverloadedLit, newIPDict, tcInstCall, + pprInstances, pprDictsTheta, pprDictsInFull, -- User error messages + showLIE, pprInst, pprInsts, pprInstInFull, -- Debugging messages + + tidyInsts, tidyMoreInsts, + + newDicts, newDictAtLoc, newDictsAtLoc, cloneDict, + shortCutFracLit, shortCutIntLit, newIPDict, + newMethod, newMethodFromName, newMethodWithGivenTy, + tcInstClassOp, tcInstStupidTheta, + tcSyntaxName, isHsVar, tyVarsOfInst, tyVarsOfInsts, tyVarsOfLIE, - ipNamesOfInst, ipNamesOfInsts, predsOfInst, predsOfInsts, + ipNamesOfInst, ipNamesOfInsts, fdPredsOfInst, fdPredsOfInsts, instLoc, getDictClassTys, dictPred, - lookupInst, lookupSimpleInst, LookupInstResult(..), + lookupInst, LookupInstResult(..), lookupPred, + tcExtendLocalInstEnv, tcGetInstEnvs, getOverlapFlag, isDict, isClassDict, isMethod, - isLinearInst, linearInstType, - isTyVarDict, isStdClassTyVarDict, isMethodFor, - instBindingRequired, instCanBeGeneralised, + isLinearInst, linearInstType, isIPDict, isInheritableInst, + isTyVarDict, isMethodFor, zonkInst, zonkInsts, instToId, instName, - InstOrigin(..), InstLoc, pprInstLoc + InstOrigin(..), InstLoc(..), pprInstLoc ) where #include "HsVersions.h" -import HsSyn ( HsLit(..), HsOverLit(..), HsExpr(..) ) -import TcHsSyn ( TcExpr, TcId, TypecheckedHsExpr, - mkHsTyApp, mkHsDictApp, mkHsConApp, zonkId - ) -import TcMonad -import TcEnv ( TcIdSet, tcGetInstEnv, tcLookupId ) -import InstEnv ( InstLookupResult(..), lookupInstEnv ) -import TcMType ( zonkTcType, zonkTcTypes, zonkTcPredType, - zonkTcThetaType, tcInstTyVar, tcInstType, +import {-# SOURCE #-} TcExpr( tcPolyExpr ) + +import HsSyn ( HsLit(..), HsOverLit(..), HsExpr(..), LHsExpr, mkHsApp, + nlHsLit, nlHsVar ) +import TcHsSyn ( mkHsTyApp, mkHsDictApp, zonkId ) +import TcRnMonad +import TcEnv ( tcLookupId, checkWellStaged, topIdLvl, tcMetaTy ) +import InstEnv ( DFunId, InstEnv, Instance(..), OverlapFlag(..), + lookupInstEnv, extendInstEnv, pprInstances, + instanceHead, instanceDFunId, setInstanceDFunId ) +import FunDeps ( checkFunDeps ) +import TcMType ( zonkTcType, zonkTcTypes, zonkTcPredType, zonkTcThetaType, + tcInstTyVar, tcInstSkolType ) -import TcType ( Type, TcType, TcThetaType, TcPredType, TcTauType, TcTyVarSet, - SourceType(..), PredType, ThetaType, TyVarDetails(VanillaTv), - tcSplitForAllTys, tcSplitForAllTys, - tcSplitMethodTy, tcSplitPhiTy, tcFunArgTy, +import TcType ( Type, TcType, TcThetaType, TcTyVarSet, TcPredType, + BoxyRhoType, + PredType(..), SkolemInfo(..), typeKind, mkSigmaTy, + tcSplitForAllTys, applyTys, + tcSplitPhiTy, tcSplitDFunHead, isIntTy,isFloatTy, isIntegerTy, isDoubleTy, - tcIsTyVarTy, mkPredTy, mkTyVarTy, mkTyVarTys, + mkPredTy, mkTyVarTys, tyVarsOfType, tyVarsOfTypes, tyVarsOfPred, tidyPred, - isClassPred, isTyVarClassPred, isLinearPred, - getClassPredTys, getClassPredTys_maybe, mkPredName, - tidyType, tidyTypes, tidyFreeTyVars, - tcCmpType, tcCmpTypes, tcCmpPred + isClassPred, isTyVarClassPred, isLinearPred, + getClassPredTys, mkPredName, + isInheritablePred, isIPPred, + tidyType, tidyTypes, tidyFreeTyVars, tcSplitSigmaTy, + pprPred, pprParendType, pprTheta ) +import Type ( TvSubst, substTy, substTyVar, substTyWith, substTheta, zipTopTvSubst, + notElemTvSubst, extendTvSubstList ) +import Unify ( tcMatchTys ) +import Kind ( isSubKind ) +import Packages ( isHomeModule ) +import HscTypes ( ExternalPackageState(..) ) import CoreFVs ( idFreeTyVars ) -import Class ( Class ) -import Id ( Id, idName, idType, mkUserLocal, mkSysLocal, mkLocalId, setIdUnique ) -import PrelInfo ( isStandardClass, isCcallishClass, isNoDictClass ) -import Name ( Name, mkMethodOcc, getOccName ) -import PprType ( pprPred, pprParendType ) -import Subst ( emptyInScopeSet, mkSubst, - substTy, substTyWith, substTheta, mkTyVarSubst, mkTopTyVarSubst - ) +import DataCon ( DataCon, dataConTyVars, dataConStupidTheta, dataConName, dataConWrapId ) +import Id ( Id, idName, idType, mkUserLocal, mkLocalId ) +import Name ( Name, mkMethodOcc, getOccName, getSrcLoc, nameModule, + isInternalName, setNameUnique ) +import NameSet ( addOneToNameSet ) import Literal ( inIntRange ) -import VarEnv ( TidyEnv, lookupSubstEnv, SubstResult(..) ) -import VarSet ( elemVarSet, emptyVarSet, unionVarSet ) +import Var ( TyVar, tyVarKind, setIdType ) +import VarEnv ( TidyEnv, emptyTidyEnv ) +import VarSet ( elemVarSet, emptyVarSet, unionVarSet, mkVarSet ) import TysWiredIn ( floatDataCon, doubleDataCon ) -import PrelNames( fromIntegerName, fromRationalName ) -import Util ( thenCmp, equalLength ) +import PrelNames ( integerTyConName, fromIntegerName, fromRationalName, rationalTyConName ) import BasicTypes( IPName(..), mapIPName, ipNameName ) - -import Bag +import UniqSupply( uniqsFromSupply ) +import SrcLoc ( mkSrcSpan, noLoc, unLoc, Located(..) ) +import DynFlags ( DynFlag(..), dopt ) +import Maybes ( isJust ) 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 - Id - TcPredType - InstLoc - - | Method - Id - - 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 - Id - HsOverLit -- The literal from the occurrence site - TcType -- The type at which the literal is used - 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 `tcCmpPred` pred2 -cmpInst (Dict _ _ _) other = LT - -cmpInst (Method _ _ _ _ _ _) (Dict _ _ _) = GT -cmpInst (Method _ id1 tys1 _ _ _) (Method _ id2 tys2 _ _ _) = (id1 `compare` id2) `thenCmp` (tys1 `tcCmpTypes` tys2) -cmpInst (Method _ _ _ _ _ _) other = LT - -cmpInst (LitInst _ lit1 ty1 _) (LitInst _ lit2 ty2 _) = (lit1 `compare` lit2) `thenCmp` (ty1 `tcCmpType` ty2) -cmpInst (LitInst _ _ _ _) other = GT - --- and they can only have HsInt or HsFracs in them. -\end{code} - Selection ~~~~~~~~~ @@ -197,48 +99,55 @@ instName :: Inst -> Name instName inst = idName (instToId inst) instToId :: Inst -> TcId -instToId (Dict id _ _) = id -instToId (Method id _ _ _ _ _) = id -instToId (LitInst id _ _ _) = id +instToId (LitInst nm _ ty _) = mkLocalId nm ty +instToId (Dict nm pred _) = mkLocalId nm (mkPredTy pred) +instToId (Method id _ _ _ _) = id -instLoc (Dict _ _ loc) = loc -instLoc (Method _ _ _ _ _ loc) = loc -instLoc (LitInst _ _ _ loc) = loc +instLoc (Dict _ _ loc) = loc +instLoc (Method _ _ _ _ loc) = loc +instLoc (LitInst _ _ _ loc) = loc dictPred (Dict _ pred _ ) = pred dictPred inst = pprPanic "dictPred" (ppr inst) getDictClassTys (Dict _ pred _) = getClassPredTys pred -predsOfInsts :: [Inst] -> [PredType] -predsOfInsts insts = concatMap predsOfInst insts +-- fdPredsOfInst is used to get predicates that contain functional +-- dependencies *or* might do so. The "might do" part is because +-- a constraint (C a b) might have a superclass with FDs +-- Leaving these in is really important for the call to fdPredsOfInsts +-- in TcSimplify.inferLoop, because the result is fed to 'grow', +-- which is supposed to be conservative +fdPredsOfInst (Dict _ pred _) = [pred] +fdPredsOfInst (Method _ _ _ theta _) = theta +fdPredsOfInst other = [] -- LitInsts etc + +fdPredsOfInsts :: [Inst] -> [PredType] +fdPredsOfInsts insts = concatMap fdPredsOfInst insts + +isInheritableInst (Dict _ pred _) = isInheritablePred pred +isInheritableInst (Method _ _ _ theta _) = all isInheritablePred theta +isInheritableInst other = True -predsOfInst (Dict _ pred _) = [pred] -predsOfInst (Method _ _ _ theta _ _) = theta -predsOfInst (LitInst _ _ _ _) = [] - -- The last case is is really a big cheat - -- LitInsts to give rise to a (Num a) or (Fractional a) predicate - -- But Num and Fractional have only one parameter and no functional - -- dependencies, so I think no caller of predsOfInst will care. 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] -ipNamesOfInst (Dict _ (IParam n _) _) = [ipNameName n] -ipNamesOfInst (Method _ _ _ theta _ _) = [ipNameName n | IParam n _ <- theta] -ipNamesOfInst other = [] +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 +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 + tyVarsOfInsts insts = foldr (unionVarSet . tyVarsOfInst) emptyVarSet insts tyVarsOfLIE lie = tyVarsOfInsts (lieToList lie) \end{code} @@ -258,13 +167,17 @@ 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 -isMethod other = False +isMethod (Method {}) = True +isMethod other = False isMethodFor :: TcIdSet -> Inst -> Bool -isMethodFor ids (Method uniq id tys _ _ loc) = id `elemVarSet` ids -isMethodFor ids inst = False +isMethodFor ids (Method uniq id tys _ loc) = id `elemVarSet` ids +isMethodFor ids inst = False isLinearInst :: Inst -> Bool isLinearInst (Dict _ pred _) = isLinearPred pred @@ -276,27 +189,8 @@ isLinearInst other = False linearInstType :: Inst -> TcType -- %x::t --> t linearInstType (Dict _ (IParam _ ty) _) = ty - - -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 -necessarily result in bindings. The first tells whether an @Inst@ -must be witnessed by an actual binding; the second tells whether an -@Inst@ can be generalised over. - -\begin{code} -instBindingRequired :: Inst -> Bool -instBindingRequired (Dict _ (ClassP clas _) _) = not (isNoDictClass clas) -instBindingRequired other = True - -instCanBeGeneralised :: Inst -> Bool -instCanBeGeneralised (Dict _ (ClassP clas _) _) = not (isCcallishClass clas) -instCanBeGeneralised other = True -\end{code} %************************************************************************ @@ -308,46 +202,49 @@ instCanBeGeneralised other = True \begin{code} newDicts :: InstOrigin -> TcThetaType - -> NF_TcM [Inst] + -> TcM [Inst] newDicts orig theta - = tcGetInstLoc orig `thenNF_Tc` \ loc -> + = getInstLoc orig `thenM` \ loc -> newDictsAtLoc loc theta -cloneDict :: Inst -> NF_TcM Inst -cloneDict (Dict id ty loc) = tcGetUnique `thenNF_Tc` \ uniq -> - returnNF_Tc (Dict (setIdUnique id uniq) ty loc) - -newDictsFromOld :: Inst -> TcThetaType -> NF_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] -newDictsAtLoc inst_loc@(_,loc,_) theta - = tcGetUniques `thenNF_Tc` \ new_uniqs -> - returnNF_Tc (zipWith mk_dict new_uniqs theta) +cloneDict :: Inst -> TcM Inst +cloneDict (Dict nm ty loc) = newUnique `thenM` \ uniq -> + returnM (Dict (setNameUnique nm uniq) ty loc) + +newDictAtLoc :: InstLoc -> TcPredType -> TcM Inst +newDictAtLoc inst_loc pred + = do { uniq <- newUnique + ; return (mkDict inst_loc uniq pred) } + +newDictsAtLoc :: InstLoc -> TcThetaType -> TcM [Inst] +newDictsAtLoc inst_loc theta + = newUniqueSupply `thenM` \ us -> + returnM (zipWith (mkDict inst_loc) (uniqsFromSupply us) theta) + +mkDict inst_loc uniq pred + = Dict name pred inst_loc where - mk_dict uniq pred = Dict (mkLocalId (mkPredName uniq loc pred) (mkPredTy pred)) pred inst_loc + name = mkPredName uniq (instLocSrcLoc inst_loc) pred -- 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 - -> NF_TcM (IPName Id, Inst) + -> TcM (IPName Id, Inst) newIPDict orig ip_name ty - = tcGetInstLoc orig `thenNF_Tc` \ inst_loc@(_,loc,_) -> - tcGetUnique `thenNF_Tc` \ uniq -> + = getInstLoc orig `thenM` \ inst_loc -> + newUnique `thenM` \ uniq -> let pred = IParam ip_name ty - id = mkLocalId (mkPredName uniq loc pred) (mkPredTy pred) + name = mkPredName uniq (instLocSrcLoc inst_loc) pred + dict = Dict name pred inst_loc in - returnNF_Tc (mapIPName (\n -> id) ip_name, Dict id pred inst_loc) + returnM (mapIPName (\n -> instToId dict) ip_name, dict) \end{code} + %************************************************************************ %* * \subsection{Building methods (calls of overloaded functions)} @@ -356,93 +253,120 @@ newIPDict orig ip_name ty \begin{code} -tcInstCall :: InstOrigin -> TcType -> NF_TcM (TypecheckedHsExpr -> TypecheckedHsExpr, LIE, TcType) -tcInstCall orig fun_ty -- fun_ty is usually a sigma-type - = tcInstType VanillaTv fun_ty `thenNF_Tc` \ (tyvars, theta, tau) -> - newDicts orig theta `thenNF_Tc` \ dicts -> - let - inst_fn e = mkHsDictApp (mkHsTyApp e (mkTyVarTys tyvars)) (map instToId dicts) - in - returnNF_Tc (inst_fn, mkLIE dicts, tau) - -newMethod :: InstOrigin - -> TcId - -> [TcType] - -> NF_TcM Inst -newMethod orig id tys - = -- Get the Id type and instantiate it at the specified types - let - (tyvars, rho) = tcSplitForAllTys (idType id) - rho_ty = substTyWith tyvars tys rho - (pred, tau) = tcSplitMethodTy rho_ty - in - newMethodWithGivenTy orig id tys [pred] tau - -newMethodWithGivenTy orig id tys theta tau - = tcGetInstLoc orig `thenNF_Tc` \ loc -> - newMethodWith loc id tys theta tau - -newMethodWith inst_loc@(_,loc,_) id tys theta tau - = tcGetUnique `thenNF_Tc` \ new_uniq -> - let - meth_id = mkUserLocal (mkMethodOcc (getOccName id)) new_uniq tau loc +tcInstStupidTheta :: DataCon -> [TcType] -> TcM () +-- Instantiate the "stupid theta" of the data con, and throw +-- the constraints into the constraint set +tcInstStupidTheta data_con inst_tys + | null stupid_theta + = return () + | otherwise + = do { stupid_dicts <- newDicts (OccurrenceOf (dataConName data_con)) + (substTheta tenv stupid_theta) + ; extendLIEs stupid_dicts } + where + stupid_theta = dataConStupidTheta data_con + tenv = zipTopTvSubst (dataConTyVars data_con) inst_tys + +newMethodFromName :: InstOrigin -> BoxyRhoType -> 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. + getInstLoc origin `thenM` \ loc -> + tcInstClassOp loc id [ty] `thenM` \ inst -> + extendLIE inst `thenM_` + returnM (instToId inst) + +newMethodWithGivenTy orig id tys + = getInstLoc orig `thenM` \ loc -> + newMethod loc id tys `thenM` \ inst -> + extendLIE inst `thenM_` + returnM (instToId inst) + +-------------------------------------------- +-- tcInstClassOp, and newMethod 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 + +-- NB: the kind of the type variable to be instantiated +-- might be a sub-kind of the type to which it is applied, +-- notably when the latter is a type variable of kind ?? +-- Hence the call to checkKind +-- A worry: is this needed anywhere else? +tcInstClassOp :: InstLoc -> Id -> [TcType] -> TcM Inst +tcInstClassOp inst_loc sel_id tys + = let + (tyvars, _rho) = tcSplitForAllTys (idType sel_id) in - returnNF_Tc (Method meth_id id tys theta tau inst_loc) - -newMethodAtLoc :: InstLoc - -> Id -> [TcType] - -> NF_TcM (Inst, TcId) -newMethodAtLoc inst_loc real_id tys - -- This actually builds the Inst - = -- Get the Id type and instantiate it at the specified types + zipWithM_ checkKind tyvars tys `thenM_` + newMethod inst_loc sel_id tys + +checkKind :: TyVar -> TcType -> TcM () +-- Ensure that the type has a sub-kind of the tyvar +checkKind tv ty + = do { let ty1 = ty + -- ty1 <- zonkTcType ty + ; if typeKind ty1 `isSubKind` tyVarKind tv + then return () + else + + pprPanic "checkKind: adding kind constraint" + (vcat [ppr tv <+> ppr (tyVarKind tv), + ppr ty <+> ppr ty1 <+> ppr (typeKind ty1)]) + } +-- do { tv1 <- tcInstTyVar tv +-- ; unifyType ty1 (mkTyVarTy tv1) } } + + +--------------------------- +newMethod inst_loc id tys + = newUnique `thenM` \ new_uniq -> let - (tyvars,rho) = tcSplitForAllTys (idType real_id) - rho_ty = ASSERT( equalLength tyvars tys ) - substTy (mkTopTyVarSubst tyvars tys) rho - (theta, tau) = tcSplitPhiTy rho_ty + (theta,tau) = tcSplitPhiTy (applyTys (idType id) tys) + meth_id = mkUserLocal (mkMethodOcc (getOccName id)) new_uniq tau loc + inst = Method meth_id id tys theta inst_loc + loc = instLocSrcLoc inst_loc in - newMethodWith inst_loc real_id tys theta tau `thenNF_Tc` \ meth_inst -> - returnNF_Tc (meth_inst, instToId meth_inst) + returnM inst \end{code} -In newOverloadedLit we convert directly to an Int or Integer if we -know that's what we want. This may save some time, by not -temporarily generating overloaded literals, but it won't catch all -cases (the rest are caught in lookupInst). - \begin{code} -newOverloadedLit :: InstOrigin - -> HsOverLit - -> TcType - -> NF_TcM (TcExpr, LIE) -newOverloadedLit orig lit ty - | Just expr <- shortCutLit lit ty - = returnNF_Tc (expr, emptyLIE) - - | otherwise - = tcGetInstLoc orig `thenNF_Tc` \ loc -> - tcGetUnique `thenNF_Tc` \ new_uniq -> - let - lit_inst = LitInst lit_id lit ty loc - lit_id = mkSysLocal FSLIT("lit") new_uniq ty - in - returnNF_Tc (HsVar (instToId lit_inst), unitLIE lit_inst) - -shortCutLit :: HsOverLit -> TcType -> Maybe TcExpr -shortCutLit (HsIntegral i fi) ty - | isIntTy ty && inIntRange i && fi == fromIntegerName -- Short cut for Int +shortCutIntLit :: Integer -> TcType -> Maybe (HsExpr TcId) +shortCutIntLit i ty + | isIntTy ty && inIntRange i -- Short cut for Int = Just (HsLit (HsInt i)) - | isIntegerTy ty && fi == fromIntegerName -- Short cut for Integer - = Just (HsLit (HsInteger i)) - -shortCutLit (HsFractional f fr) ty - | isFloatTy ty && fr == fromRationalName - = Just (mkHsConApp floatDataCon [] [HsLit (HsFloatPrim f)]) - | isDoubleTy ty && fr == fromRationalName - = Just (mkHsConApp doubleDataCon [] [HsLit (HsDoublePrim f)]) - -shortCutLit lit ty - = Nothing + | isIntegerTy ty -- Short cut for Integer + = Just (HsLit (HsInteger i ty)) + | otherwise = Nothing + +shortCutFracLit :: Rational -> TcType -> Maybe (HsExpr TcId) +shortCutFracLit f ty + | isFloatTy ty + = Just (mk_lit floatDataCon (HsFloatPrim f)) + | isDoubleTy ty + = Just (mk_lit doubleDataCon (HsDoublePrim f)) + | otherwise = Nothing + where + mk_lit con lit = HsApp (nlHsVar (dataConWrapId con)) (nlHsLit lit) + +mkIntegerLit :: Integer -> TcM (LHsExpr TcId) +mkIntegerLit i + = tcMetaTy integerTyConName `thenM` \ integer_ty -> + getSrcSpanM `thenM` \ span -> + returnM (L span $ HsLit (HsInteger i integer_ty)) + +mkRatLit :: Rational -> TcM (LHsExpr TcId) +mkRatLit r + = tcMetaTy rationalTyConName `thenM` \ rat_ty -> + getSrcSpanM `thenM` \ span -> + returnM (L span $ HsLit (HsRat r rat_ty)) + +isHsVar :: HsExpr Name -> Name -> Bool +isHsVar (HsVar f) g = f==g +isHsVar other g = False \end{code} @@ -452,32 +376,29 @@ shortCutLit lit ty %* * %************************************************************************ -Zonking makes sure that the instance types are fully zonked, -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. +Zonking makes sure that the instance types are fully zonked. \begin{code} -zonkInst :: Inst -> NF_TcM Inst -zonkInst (Dict id pred loc) - = zonkTcPredType pred `thenNF_Tc` \ new_pred -> - returnNF_Tc (Dict id new_pred loc) +zonkInst :: Inst -> TcM Inst +zonkInst (Dict name pred loc) + = zonkTcPredType pred `thenM` \ new_pred -> + returnM (Dict name new_pred loc) -zonkInst (Method m id tys theta tau loc) - = zonkId id `thenNF_Tc` \ new_id -> +zonkInst (Method m id tys theta 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 m new_id new_tys new_theta new_tau loc) + zonkTcTypes tys `thenM` \ new_tys -> + zonkTcThetaType theta `thenM` \ new_theta -> + returnM (Method m new_id new_tys new_theta loc) -zonkInst (LitInst id lit ty loc) - = zonkTcType ty `thenNF_Tc` \ new_ty -> - returnNF_Tc (LitInst id lit new_ty loc) +zonkInst (LitInst nm lit ty loc) + = zonkTcType ty `thenM` \ new_ty -> + returnM (LitInst nm lit new_ty loc) -zonkInsts insts = mapNF_Tc zonkInst insts +zonkInsts insts = mappM zonkInst insts \end{code} @@ -494,25 +415,38 @@ relevant in error messages. instance Outputable Inst where ppr inst = pprInst inst -pprInst (LitInst u lit ty loc) - = hsep [ppr lit, ptext SLIT("at"), ppr ty, show_uniq u] +pprDictsTheta :: [Inst] -> SDoc +-- Print in type-like fashion (Eq a, Show b) +pprDictsTheta dicts = pprTheta (map dictPred dicts) + +pprDictsInFull :: [Inst] -> SDoc +-- Print in type-like fashion, but with source location +pprDictsInFull dicts + = vcat (map go dicts) + where + go dict = sep [quotes (ppr (dictPred dict)), nest 2 (pprInstLoc (instLoc dict))] + +pprInsts :: [Inst] -> SDoc +-- Debugging: print the evidence :: type +pprInsts insts = brackets (interpp'SP insts) -pprInst (Dict u pred loc) = pprPred pred <+> show_uniq u +pprInst, pprInstInFull :: Inst -> SDoc +-- Debugging: print the evidence :: type +pprInst (LitInst nm lit ty loc) = ppr nm <+> dcolon <+> ppr ty +pprInst (Dict nm pred loc) = ppr nm <+> dcolon <+> pprPred pred -pprInst m@(Method u id tys theta tau loc) - = hsep [ppr id, ptext SLIT("at"), - brackets (sep (map pprParendType tys)) {- , - ptext SLIT("theta"), ppr theta, - ptext SLIT("tau"), ppr tau - show_uniq u, - ppr (instToId m) -}] +pprInst m@(Method inst_id id tys theta loc) + = ppr inst_id <+> dcolon <+> + braces (sep [ppr id <+> ptext SLIT("at"), + brackets (sep (map pprParendType tys))]) -show_uniq u = ifPprDebug (text "{-" <> ppr u <> text "-}") +pprInstInFull inst + = sep [quotes (pprInst inst), nest 2 (pprInstLoc (instLoc inst))] 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 (LitInst nm lit ty loc) = LitInst nm lit (tidyType env ty) loc +tidyInst env (Dict nm pred loc) = Dict nm (tidyPred env pred) loc +tidyInst env (Method u id tys theta loc) = Method u id (tidyTypes env tys) theta loc tidyMoreInsts :: TidyEnv -> [Inst] -> (TidyEnv, [Inst]) -- This function doesn't assume that the tyvars are in scope @@ -524,118 +458,333 @@ tidyMoreInsts env insts tidyInsts :: [Inst] -> (TidyEnv, [Inst]) tidyInsts insts = tidyMoreInsts emptyTidyEnv insts + +showLIE :: SDoc -> TcM () -- Debugging +showLIE str + = do { lie_var <- getLIEVar ; + lie <- readMutVar lie_var ; + traceTc (str <+> vcat (map pprInstInFull (lieToList lie))) } \end{code} %************************************************************************ %* * + Extending the instance environment +%* * +%************************************************************************ + +\begin{code} +tcExtendLocalInstEnv :: [Instance] -> TcM a -> TcM a + -- Add new locally-defined instances +tcExtendLocalInstEnv dfuns thing_inside + = do { traceDFuns dfuns + ; env <- getGblEnv + ; inst_env' <- foldlM addLocalInst (tcg_inst_env env) dfuns + ; let env' = env { tcg_insts = dfuns ++ tcg_insts env, + tcg_inst_env = inst_env' } + ; setGblEnv env' thing_inside } + +addLocalInst :: InstEnv -> Instance -> TcM InstEnv +-- Check that the proposed new instance is OK, +-- and then add it to the home inst env +addLocalInst home_ie ispec + = do { -- Instantiate the dfun type so that we extend the instance + -- envt with completely fresh template variables + -- This is important because the template variables must + -- not overlap with anything in the things being looked up + -- (since we do unification). + -- We use tcInstSkolType because we don't want to allocate fresh + -- *meta* type variables. + let dfun = instanceDFunId ispec + ; (tvs', theta', tau') <- tcInstSkolType (InstSkol dfun) (idType dfun) + ; let (cls, tys') = tcSplitDFunHead tau' + dfun' = setIdType dfun (mkSigmaTy tvs' theta' tau') + ispec' = setInstanceDFunId ispec dfun' + + -- Load imported instances, so that we report + -- duplicates correctly + ; eps <- getEps + ; let inst_envs = (eps_inst_env eps, home_ie) + + -- Check functional dependencies + ; case checkFunDeps inst_envs ispec' of + Just specs -> funDepErr ispec' specs + Nothing -> return () + + -- Check for duplicate instance decls + ; let { (matches, _) = lookupInstEnv inst_envs cls tys' + ; dup_ispecs = [ dup_ispec + | (_, dup_ispec) <- matches + , let (_,_,_,dup_tys) = instanceHead dup_ispec + , isJust (tcMatchTys (mkVarSet tvs') tys' dup_tys)] } + -- Find memebers of the match list which ispec itself matches. + -- If the match is 2-way, it's a duplicate + ; case dup_ispecs of + dup_ispec : _ -> dupInstErr ispec' dup_ispec + [] -> return () + + -- OK, now extend the envt + ; return (extendInstEnv home_ie ispec') } + +getOverlapFlag :: TcM OverlapFlag +getOverlapFlag + = do { dflags <- getDOpts + ; let overlap_ok = dopt Opt_AllowOverlappingInstances dflags + incoherent_ok = dopt Opt_AllowIncoherentInstances dflags + overlap_flag | incoherent_ok = Incoherent + | overlap_ok = OverlapOk + | otherwise = NoOverlap + + ; return overlap_flag } + +traceDFuns ispecs + = traceTc (hang (text "Adding instances:") 2 (vcat (map pp ispecs))) + where + pp ispec = ppr (instanceDFunId ispec) <+> colon <+> ppr ispec + -- Print the dfun name itself too + +funDepErr ispec ispecs + = addDictLoc ispec $ + addErr (hang (ptext SLIT("Functional dependencies conflict between instance declarations:")) + 2 (pprInstances (ispec:ispecs))) +dupInstErr ispec dup_ispec + = addDictLoc ispec $ + addErr (hang (ptext SLIT("Duplicate instance declarations:")) + 2 (pprInstances [ispec, dup_ispec])) + +addDictLoc ispec thing_inside + = setSrcSpan (mkSrcSpan loc loc) thing_inside + where + loc = getSrcLoc ispec +\end{code} + + +%************************************************************************ +%* * \subsection{Looking up Insts} %* * %************************************************************************ \begin{code} -data LookupInstResult s +data LookupInstResult = NoInstance - | SimpleInst TcExpr -- Just a variable, type application, or literal - | GenInst [Inst] TcExpr -- The expression and its needed insts + | SimpleInst (LHsExpr TcId) -- Just a variable, type application, or literal + | GenInst [Inst] (LHsExpr TcId) -- The expression and its needed insts -lookupInst :: Inst - -> NF_TcM (LookupInstResult s) +lookupInst :: Inst -> TcM LookupInstResult +-- 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 _ (ClassP clas tys) loc) - = getDOptsTc `thenNF_Tc` \ dflags -> - tcGetInstEnv `thenNF_Tc` \ inst_env -> - case lookupInstEnv dflags inst_env clas tys of - - FoundInst tenv dfun_id - -> -- 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) -> returnNF_Tc ty - Nothing -> tcInstTyVar VanillaTv tv `thenNF_Tc` \ tc_tv -> - returnTc (mkTyVarTy tc_tv) - in - mapNF_Tc mk_ty_arg tyvars `thenNF_Tc` \ 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) - else - newDictsAtLoc loc theta `thenNF_Tc` \ dicts -> - let - rhs = mkHsDictApp ty_app (map instToId dicts) - in - returnNF_Tc (GenInst dicts rhs) - - other -> returnNF_Tc NoInstance - -lookupInst dict@(Dict _ _ loc) = returnNF_Tc NoInstance -- Methods -lookupInst inst@(Method _ id tys theta _ loc) - = newDictsAtLoc loc theta `thenNF_Tc` \ dicts -> - returnNF_Tc (GenInst dicts (mkHsDictApp (mkHsTyApp (HsVar id) tys) (map instToId dicts))) +lookupInst inst@(Method _ id tys theta loc) + = newDictsAtLoc loc theta `thenM` \ dicts -> + returnM (GenInst dicts (mkHsDictApp (mkHsTyApp (L span (HsVar id)) tys) (map instToId dicts))) + where + span = instLocSrcSpan loc -- Literals -- 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). +-- 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 lit ty loc) - | Just expr <- shortCutLit lit ty - = returnNF_Tc (GenInst [] expr) -- GenInst, not SimpleInst, because +lookupInst inst@(LitInst _nm (HsIntegral i from_integer_name) ty loc) + | Just expr <- shortCutIntLit i ty + = returnM (GenInst [] (noLoc expr)) -- GenInst, not SimpleInst, because -- expr may be a constructor application + | otherwise + = ASSERT( from_integer_name `isHsVar` fromIntegerName ) -- A LitInst invariant + tcLookupId fromIntegerName `thenM` \ from_integer -> + tcInstClassOp loc from_integer [ty] `thenM` \ method_inst -> + mkIntegerLit i `thenM` \ integer_lit -> + returnM (GenInst [method_inst] + (mkHsApp (L (instLocSrcSpan loc) + (HsVar (instToId method_inst))) integer_lit)) + +lookupInst inst@(LitInst _nm (HsFractional f from_rat_name) ty loc) + | Just expr <- shortCutFracLit f ty + = returnM (GenInst [] (noLoc expr)) -lookupInst inst@(LitInst u (HsIntegral i from_integer_name) ty loc) - = tcLookupId 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) (HsLit (HsInteger i)))) - + | otherwise + = ASSERT( from_rat_name `isHsVar` fromRationalName ) -- A LitInst invariant + tcLookupId fromRationalName `thenM` \ from_rational -> + tcInstClassOp loc from_rational [ty] `thenM` \ method_inst -> + mkRatLit f `thenM` \ rat_lit -> + returnM (GenInst [method_inst] (mkHsApp (L (instLocSrcSpan loc) + (HsVar (instToId method_inst))) rat_lit)) -lookupInst inst@(LitInst u (HsFractional f from_rat_name) ty loc) - = tcLookupId from_rat_name `thenNF_Tc` \ from_rational -> - newMethodAtLoc loc from_rational [ty] `thenNF_Tc` \ (method_inst, method_id) -> - let - rational_ty = tcFunArgTy (idType method_id) - rational_lit = HsLit (HsRat f rational_ty) - in - returnNF_Tc (GenInst [method_inst] (HsApp (HsVar method_id) rational_lit)) +-- Dictionaries +lookupInst (Dict _ pred loc) + = do { mb_result <- lookupPred pred + ; case mb_result of { + Nothing -> return NoInstance ; + Just (tenv, dfun_id) -> do + + -- tenv is a substitution that instantiates the dfun_id + -- to match the requested result type. + -- + -- We ASSUME that the dfun is quantified over the very same tyvars + -- that are bound by the tenv. + -- + -- However, the dfun + -- might have some tyvars that *only* appear in arguments + -- dfun :: forall a b. C a b, Ord b => D [a] + -- We instantiate b to a flexi type variable -- it'll presumably + -- become fixed later via functional dependencies + { use_stage <- getStage + ; checkWellStaged (ptext SLIT("instance for") <+> quotes (ppr pred)) + (topIdLvl dfun_id) use_stage + + -- 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 open_tvs to instantiate any un-substituted tyvars. + ; let (tyvars, rho) = tcSplitForAllTys (idType dfun_id) + open_tvs = filter (`notElemTvSubst` tenv) tyvars + ; open_tvs' <- mappM tcInstTyVar open_tvs + ; let + tenv' = extendTvSubstList tenv open_tvs (mkTyVarTys open_tvs') + -- Since the open_tvs' are freshly made, they cannot possibly be captured by + -- any nested for-alls in rho. So the in-scope set is unchanged + dfun_rho = substTy tenv' rho + (theta, _) = tcSplitPhiTy dfun_rho + ty_app = mkHsTyApp (L (instLocSrcSpan loc) (HsVar dfun_id)) + (map (substTyVar tenv') tyvars) + ; if null theta then + returnM (SimpleInst ty_app) + else do + { dicts <- newDictsAtLoc loc theta + ; let rhs = mkHsDictApp ty_app (map instToId dicts) + ; returnM (GenInst dicts rhs) + }}}} + +--------------- +lookupPred :: TcPredType -> TcM (Maybe (TvSubst, DFunId)) +-- Look up a class constraint in the instance environment +lookupPred pred@(ClassP clas tys) + = do { eps <- getEps + ; tcg_env <- getGblEnv + ; let inst_envs = (eps_inst_env eps, tcg_inst_env tcg_env) + ; case lookupInstEnv inst_envs clas tys of { + ([(tenv, ispec)], []) + -> do { let dfun_id = is_dfun ispec + ; traceTc (text "lookupInst success" <+> + vcat [text "dict" <+> ppr pred, + text "witness" <+> ppr dfun_id + <+> ppr (idType dfun_id) ]) + -- Record that this dfun is needed + ; record_dfun_usage dfun_id + ; return (Just (tenv, dfun_id)) } ; + + (matches, unifs) + -> do { traceTc (text "lookupInst fail" <+> + vcat [text "dict" <+> ppr pred, + text "matches" <+> ppr matches, + text "unifs" <+> ppr unifs]) + -- In the case of overlap (multiple matches) we report + -- NoInstance here. That has the effect of making the + -- context-simplifier return the dict as an irreducible one. + -- Then it'll be given to addNoInstanceErrs, which will do another + -- lookupInstEnv to get the detailed info about what went wrong. + ; return Nothing } + }} + +lookupPred ip_pred = return Nothing + +record_dfun_usage dfun_id + = do { gbl <- getGblEnv + ; let dfun_name = idName dfun_id + dfun_mod = nameModule dfun_name + ; if isInternalName dfun_name || -- Internal name => defined in this module + not (isHomeModule (tcg_home_mods gbl) dfun_mod) + then return () -- internal, or in another package + else do { tcg_env <- getGblEnv + ; updMutVar (tcg_inst_uses tcg_env) + (`addOneToNameSet` idName dfun_id) }} + + +tcGetInstEnvs :: TcM (InstEnv, InstEnv) +-- Gets both the external-package inst-env +-- and the home-pkg inst env (includes module being compiled) +tcGetInstEnvs = do { eps <- getEps; env <- getGblEnv; + return (eps_inst_env eps, tcg_inst_env env) } \end{code} -There is a second, simpler interface, when you want an instance of a -class at a given nullary type constructor. It just returns the -appropriate dictionary if it exists. It is used only when resolving -ambiguous dictionaries. + + +%************************************************************************ +%* * + 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} -lookupSimpleInst :: Class - -> [Type] -- Look up (c,t) - -> NF_TcM (Maybe ThetaType) -- Here are the needed (c,t)s - -lookupSimpleInst clas tys - = getDOptsTc `thenNF_Tc` \ dflags -> - tcGetInstEnv `thenNF_Tc` \ inst_env -> - case lookupInstEnv dflags inst_env clas tys of - FoundInst tenv dfun - -> returnNF_Tc (Just (substTheta (mkSubst emptyInScopeSet tenv) theta)) - where - (_, rho) = tcSplitForAllTys (idType dfun) - (theta,_) = tcSplitPhiTy rho - - other -> returnNF_Tc Nothing +tcSyntaxName :: InstOrigin + -> TcType -- Type to instantiate it at + -> (Name, HsExpr Name) -- (Standard name, user name) + -> TcM (Name, HsExpr TcId) -- (Standard name, suitable expression) +-- *** NOW USED ONLY FOR CmdTop (sigh) *** +-- 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, HsVar user_nm) + | std_nm == user_nm + = newMethodFromName orig ty std_nm `thenM` \ id -> + returnM (std_nm, HsVar id) + +tcSyntaxName orig ty (std_nm, user_nm_expr) + = tcLookupId std_nm `thenM` \ std_id -> + let + -- C.f. newMethodAtLoc + ([tv], _, tau) = tcSplitSigmaTy (idType std_id) + sigma1 = substTyWith [tv] [ty] tau + -- Actually, the "tau-type" might be a sigma-type in the + -- case of locally-polymorphic methods. + in + addErrCtxtM (syntaxNameCtxt user_nm_expr orig sigma1) $ + + -- Check that the user-supplied thing has the + -- same type as the standard one. + -- Tiresome jiggling because tcCheckSigma takes a located expression + getSrcSpanM `thenM` \ span -> + tcPolyExpr (L span user_nm_expr) sigma1 `thenM` \ expr -> + returnM (std_nm, unLoc expr) + +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}