X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=blobdiff_plain;f=compiler%2Ftypecheck%2FInst.lhs;h=13b8be80b8fdcd3f3bb9ea3de8237bba4bd7d0b2;hp=b0fe5f95cb8116df90697e653ea26a6c69962637;hb=4ba96c06f2b69ea1fe2b27718013713e94c1520c;hpb=0aa1d46a1e5c19553c410dc6ff65b29594a2499f diff --git a/compiler/typecheck/Inst.lhs b/compiler/typecheck/Inst.lhs index b0fe5f9..13b8be8 100644 --- a/compiler/typecheck/Inst.lhs +++ b/compiler/typecheck/Inst.lhs @@ -6,6 +6,13 @@ The @Inst@ type: dictionaries or method instances \begin{code} +{-# OPTIONS -w #-} +-- The above warning supression flag is a temporary kludge. +-- While working on this module you are encouraged to remove it and fix +-- any warnings in the module. See +-- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings +-- for details + module Inst ( Inst, @@ -17,7 +24,7 @@ module Inst ( newDictBndr, newDictBndrs, newDictBndrsO, instCall, instStupidTheta, cloneDict, - shortCutFracLit, shortCutIntLit, newIPDict, + shortCutFracLit, shortCutIntLit, shortCutStringLit, newIPDict, newMethod, newMethodFromName, newMethodWithGivenTy, tcInstClassOp, tcSyntaxName, isHsVar, @@ -26,24 +33,34 @@ module Inst ( ipNamesOfInst, ipNamesOfInsts, fdPredsOfInst, fdPredsOfInsts, getDictClassTys, dictPred, - lookupSimpleInst, LookupInstResult(..), lookupPred, + lookupSimpleInst, LookupInstResult(..), tcExtendLocalInstEnv, tcGetInstEnvs, getOverlapFlag, + isAbstractableInst, isEqInst, isDict, isClassDict, isMethod, isImplicInst, isIPDict, isInheritableInst, isMethodOrLit, - isTyVarDict, isMethodFor, getDefaultableDicts, + isTyVarDict, isMethodFor, zonkInst, zonkInsts, - instToId, instToVar, instName, + instToId, instToVar, instType, instName, + + InstOrigin(..), InstLoc, pprInstLoc, - InstOrigin(..), InstLoc, pprInstLoc + mkWantedCo, mkGivenCo, + fromWantedCo, fromGivenCo, + eitherEqInst, mkEqInst, mkEqInsts, mkWantedEqInst, + finalizeEqInst, writeWantedCoercion, + eqInstType, updateEqInstCoercion, + eqInstCoercion, + eqInstLeftTy, eqInstRightTy ) where #include "HsVersions.h" import {-# SOURCE #-} TcExpr( tcPolyExpr ) -import {-# SOURCE #-} TcUnify( unifyType ) +import {-# SOURCE #-} TcUnify( boxyUnify, unifyType ) +import FastString(FastString) import HsSyn import TcHsSyn import TcRnMonad @@ -53,6 +70,7 @@ import FunDeps import TcMType import TcType import Type +import TypeRep import Class import Unify import Module @@ -76,6 +94,9 @@ import DynFlags import Maybes import Util import Outputable +import Data.List +import TypeRep +import Class \end{code} @@ -83,10 +104,12 @@ Selection ~~~~~~~~~ \begin{code} instName :: Inst -> Name +instName (EqInst {tci_name = name}) = name instName inst = Var.varName (instToVar inst) instToId :: Inst -> TcId -instToId inst = ASSERT2( isId id, ppr inst ) id +instToId inst = WARN( not (isId id), ppr inst ) + id where id = instToVar inst @@ -101,25 +124,33 @@ instToVar (Dict {tci_name = nm, tci_pred = pred}) instToVar (ImplicInst {tci_name = nm, tci_tyvars = tvs, tci_given = givens, tci_wanted = wanteds}) = mkLocalId nm (mkImplicTy tvs givens wanteds) +instToVar i@(EqInst {}) + = eitherEqInst i id (\(TyVarTy covar) -> covar) instType :: Inst -> Type -instType (LitInst {tci_ty = ty}) = ty -instType (Method {tci_id = id}) = idType id +instType (LitInst {tci_ty = ty}) = ty +instType (Method {tci_id = id}) = idType id instType (Dict {tci_pred = pred}) = mkPredTy pred instType imp@(ImplicInst {}) = mkImplicTy (tci_tyvars imp) (tci_given imp) (tci_wanted imp) +-- instType i@(EqInst {tci_co = co}) = eitherEqInst i TyVarTy id +instType (EqInst {tci_left = ty1, tci_right = ty2}) = mkPredTy (EqPred ty1 ty2) mkImplicTy tvs givens wanteds -- The type of an implication constraint = ASSERT( all isDict givens ) -- pprTrace "mkImplicTy" (ppr givens) $ - mkForAllTys tvs $ - mkPhiTy (map dictPred givens) $ - if isSingleton wanteds then - instType (head wanteds) - else - mkTupleTy Boxed (length wanteds) (map instType wanteds) + -- See [Equational Constraints in Implication Constraints] + let dict_wanteds = filter (not . isEqInst) wanteds + in + mkForAllTys tvs $ + mkPhiTy (map dictPred givens) $ + if isSingleton dict_wanteds then + instType (head dict_wanteds) + else + mkTupleTy Boxed (length dict_wanteds) (map instType dict_wanteds) dictPred (Dict {tci_pred = pred}) = pred +dictPred (EqInst {tci_left=ty1,tci_right=ty2}) = EqPred ty1 ty2 dictPred inst = pprPanic "dictPred" (ppr inst) getDictClassTys (Dict {tci_pred = pred}) = getClassPredTys pred @@ -136,6 +167,7 @@ fdPredsOfInst (Method {tci_theta = theta}) = theta fdPredsOfInst (ImplicInst {tci_given = gs, tci_wanted = ws}) = fdPredsOfInsts (gs ++ ws) fdPredsOfInst (LitInst {}) = [] +fdPredsOfInst (EqInst {}) = [] fdPredsOfInsts :: [Inst] -> [PredType] fdPredsOfInsts insts = concatMap fdPredsOfInst insts @@ -161,12 +193,15 @@ ipNamesOfInst other = [] tyVarsOfInst :: Inst -> TcTyVarSet tyVarsOfInst (LitInst {tci_ty = ty}) = tyVarsOfType ty tyVarsOfInst (Dict {tci_pred = pred}) = tyVarsOfPred pred -tyVarsOfInst (Method {tci_oid = id, tci_tys = tys}) = tyVarsOfTypes tys `unionVarSet` idFreeTyVars id +tyVarsOfInst (Method {tci_oid = id, tci_tys = tys}) = tyVarsOfTypes tys `unionVarSet` varTypeTyVars id -- The id might have free type variables; in the case of -- locally-overloaded class methods, for example tyVarsOfInst (ImplicInst {tci_tyvars = tvs, tci_given = givens, tci_wanted = wanteds}) - = (tyVarsOfInsts givens `unionVarSet` tyVarsOfInsts wanteds) `minusVarSet` mkVarSet tvs - + = (tyVarsOfInsts givens `unionVarSet` tyVarsOfInsts wanteds) + `minusVarSet` mkVarSet tvs + `unionVarSet` unionVarSets (map varTypeTyVars tvs) + -- Remember the free tyvars of a coercion +tyVarsOfInst (EqInst {tci_left = ty1, tci_right = ty2}) = tyVarsOfType ty1 `unionVarSet` tyVarsOfType ty2 tyVarsOfInsts insts = foldr (unionVarSet . tyVarsOfInst) emptyVarSet insts tyVarsOfLIE lie = tyVarsOfInsts (lieToList lie) @@ -175,6 +210,14 @@ tyVarsOfLIE lie = tyVarsOfInsts (lieToList lie) Predicates ~~~~~~~~~~ \begin{code} + +isAbstractableInst :: Inst -> Bool +isAbstractableInst inst = isDict inst || isEqInst inst + +isEqInst :: Inst -> Bool +isEqInst (EqInst {}) = True +isEqInst other = False + isDict :: Inst -> Bool isDict (Dict {}) = True isDict other = False @@ -208,26 +251,6 @@ isMethodOrLit (LitInst {}) = True isMethodOrLit other = False \end{code} -\begin{code} -getDefaultableDicts :: [Inst] -> ([(Inst, Class, TcTyVar)], TcTyVarSet) --- Look for free dicts of the form (C tv), even inside implications --- *and* the set of tyvars mentioned by all *other* constaints --- This disgustingly ad-hoc function is solely to support defaulting -getDefaultableDicts insts - = (concat ps, unionVarSets tvs) - where - (ps, tvs) = mapAndUnzip get insts - get d@(Dict {tci_pred = ClassP cls [ty]}) - | Just tv <- tcGetTyVar_maybe ty = ([(d,cls,tv)], emptyVarSet) - | otherwise = ([], tyVarsOfType ty) - get (ImplicInst {tci_tyvars = tvs, tci_wanted = wanteds}) - = ([ up | up@(_,_,tv) <- ups, not (tv `elemVarSet` tv_set)], - ftvs `minusVarSet` tv_set) - where - tv_set = mkVarSet tvs - (ups, ftvs) = getDefaultableDicts wanteds - get inst = ([], tyVarsOfInst inst) -\end{code} %************************************************************************ %* * @@ -249,6 +272,15 @@ newDictBndrs :: InstLoc -> TcThetaType -> TcM [Inst] newDictBndrs inst_loc theta = mapM (newDictBndr inst_loc) theta newDictBndr :: InstLoc -> TcPredType -> TcM Inst +newDictBndr inst_loc pred@(EqPred ty1 ty2) + = do { uniq <- newUnique + ; let name = mkPredName uniq inst_loc pred + ; return (EqInst {tci_name = name, + tci_loc = inst_loc, + tci_left = ty1, + tci_right = ty2, + tci_co = mkGivenCo $ TyVarTy (Var.mkCoVar name (PredTy pred))}) + } newDictBndr inst_loc pred = do { uniq <- newUnique ; let name = mkPredName uniq inst_loc pred @@ -260,12 +292,11 @@ instCall :: InstOrigin -> [TcType] -> TcThetaType -> TcM HsWrapper -- (instCall o tys theta) -- (a) Makes fresh dictionaries as necessary for the constraints (theta) -- (b) Throws these dictionaries into the LIE --- (c) Eeturns an HsWrapper ([.] tys dicts) +-- (c) Returns an HsWrapper ([.] tys dicts) instCall orig tys theta = do { loc <- getInstLoc orig - ; (dicts, dict_app) <- instCallDicts loc theta - ; extendLIEs dicts + ; dict_app <- instCallDicts loc theta ; return (dict_app <.> mkWpTyApps tys) } ---------------- @@ -274,35 +305,47 @@ instStupidTheta :: InstOrigin -> TcThetaType -> TcM () -- Used exclusively for the 'stupid theta' of a data constructor instStupidTheta orig theta = do { loc <- getInstLoc orig - ; (dicts, _) <- instCallDicts loc theta - ; extendLIEs dicts } + ; _co <- instCallDicts loc theta -- Discard the coercion + ; return () } ---------------- -instCallDicts :: InstLoc -> TcThetaType -> TcM ([Inst], HsWrapper) +instCallDicts :: InstLoc -> TcThetaType -> TcM HsWrapper +-- Instantiates the TcTheta, puts all constraints thereby generated +-- into the LIE, and returns a HsWrapper to enclose the call site. -- This is the key place where equality predicates -- are unleashed into the world -instCallDicts loc [] = return ([], idHsWrapper) +instCallDicts loc [] = return idHsWrapper + +-- instCallDicts loc (EqPred ty1 ty2 : preds) +-- = do { unifyType ty1 ty2 -- For now, we insist that they unify right away +-- -- Later on, when we do associated types, +-- -- unifyType :: Type -> Type -> TcM ([Inst], Coercion) +-- ; (dicts, co_fn) <- instCallDicts loc preds +-- ; return (dicts, co_fn <.> WpTyApp ty1) } +-- -- We use type application to apply the function to the +-- -- coercion; here ty1 *is* the appropriate identity coercion instCallDicts loc (EqPred ty1 ty2 : preds) - = do { unifyType ty1 ty2 -- For now, we insist that they unify right away - -- Later on, when we do associated types, - -- unifyType :: Type -> Type -> TcM ([Inst], Coercion) - ; (dicts, co_fn) <- instCallDicts loc preds - ; return (dicts, co_fn <.> WpTyApp ty1) } - -- We use type application to apply the function to the - -- coercion; here ty1 *is* the appropriate identity coercion + = do { traceTc (text "instCallDicts" <+> ppr (EqPred ty1 ty2)) + ; coi <- boxyUnify ty1 ty2 +-- ; coi <- unifyType ty1 ty2 + ; let co = fromCoI coi ty1 + ; co_fn <- instCallDicts loc preds + ; return (co_fn <.> WpTyApp co) } instCallDicts loc (pred : preds) = do { uniq <- newUnique ; let name = mkPredName uniq loc pred dict = Dict {tci_name = name, tci_pred = pred, tci_loc = loc} - ; (dicts, co_fn) <- instCallDicts loc preds - ; return (dict:dicts, co_fn <.> WpApp (instToId dict)) } + ; extendLIE dict + ; co_fn <- instCallDicts loc preds + ; return (co_fn <.> WpApp (instToId dict)) } ------------- -cloneDict :: Inst -> TcM Inst -- Only used for linear implicit params +cloneDict :: Inst -> TcM Inst cloneDict dict@(Dict nm ty loc) = do { uniq <- newUnique ; return (dict {tci_name = setNameUnique nm uniq}) } +cloneDict eq@(EqInst {}) = return eq cloneDict other = pprPanic "cloneDict" (ppr other) -- For vanilla implicit parameters, there is only one in scope @@ -326,18 +369,17 @@ newIPDict orig ip_name ty \begin{code} mkPredName :: Unique -> InstLoc -> PredType -> Name mkPredName uniq loc pred_ty - = mkInternalName uniq occ (srcSpanStart (instLocSpan loc)) + = mkInternalName uniq occ (instLocSpan loc) where occ = case pred_ty of ClassP cls _ -> mkDictOcc (getOccName cls) IParam ip _ -> getOccName (ipNameName ip) EqPred ty _ -> mkEqPredCoOcc baseOcc where - -- we use the outermost tycon of the lhs, which must be a type - -- function, as the base name for an equality + -- we use the outermost tycon of the lhs, if there is one, to + -- improve readability of Core code baseOcc = case splitTyConApp_maybe ty of - Nothing -> - pprPanic "Inst.mkPredName:" (ppr ty) + Nothing -> mkOccName tcName "$" Just (tc, _) -> getOccName tc \end{code} @@ -411,7 +453,7 @@ newMethod inst_loc id tys meth_id = mkUserLocal (mkMethodOcc (getOccName id)) new_uniq tau loc inst = Method {tci_id = meth_id, tci_oid = id, tci_tys = tys, tci_theta = theta, tci_loc = inst_loc} - loc = srcSpanStart (instLocSpan inst_loc) + loc = instLocSpan inst_loc in returnM inst \end{code} @@ -435,6 +477,12 @@ shortCutFracLit f ty where mk_lit con lit = HsApp (nlHsVar (dataConWrapId con)) (nlHsLit lit) +shortCutStringLit :: FastString -> TcType -> Maybe (HsExpr TcId) +shortCutStringLit s ty + | isStringTy ty -- Short cut for String + = Just (HsLit (HsString s)) + | otherwise = Nothing + mkIntegerLit :: Integer -> TcM (LHsExpr TcId) mkIntegerLit i = tcMetaTy integerTyConName `thenM` \ integer_ty -> @@ -447,6 +495,12 @@ mkRatLit r getSrcSpanM `thenM` \ span -> returnM (L span $ HsLit (HsRat r rat_ty)) +mkStrLit :: FastString -> TcM (LHsExpr TcId) +mkStrLit s + = --tcMetaTy stringTyConName `thenM` \ string_ty -> + getSrcSpanM `thenM` \ span -> + returnM (L span $ HsLit (HsString s)) + isHsVar :: HsExpr Name -> Name -> Bool isHsVar (HsVar f) g = f==g isHsVar other g = False @@ -488,6 +542,15 @@ zonkInst implic@(ImplicInst {}) ; wanteds' <- zonkInsts (tci_wanted implic) ; return (implic {tci_given = givens',tci_wanted = wanteds'}) } +zonkInst eqinst@(EqInst {tci_left = ty1, tci_right = ty2}) + = do { co' <- eitherEqInst eqinst + (\covar -> return (mkWantedCo covar)) + (\co -> zonkTcType co >>= \coercion -> return (mkGivenCo coercion)) + ; ty1' <- zonkTcType ty1 + ; ty2' <- zonkTcType ty2 + ; return (eqinst {tci_co = co',tci_left=ty1',tci_right=ty2}) + } + zonkInsts insts = mappM zonkInst insts \end{code} @@ -523,6 +586,10 @@ pprInsts insts = brackets (interpp'SP insts) pprInst, pprInstInFull :: Inst -> SDoc -- Debugging: print the evidence :: type +pprInst i@(EqInst {tci_left = ty1, tci_right = ty2, tci_co = co}) + = eitherEqInst i + (\covar -> text "Wanted" <+> ppr (TyVarTy covar) <+> dcolon <+> ppr (EqPred ty1 ty2)) + (\co -> text "Given" <+> ppr co <+> dcolon <+> ppr (EqPred ty1 ty2)) pprInst inst = ppr (instName inst) <+> dcolon <+> (braces (ppr (instType inst)) $$ ifPprDebug implic_stuff) @@ -530,9 +597,15 @@ pprInst inst = ppr (instName inst) <+> dcolon implic_stuff | isImplicInst inst = ppr (tci_reft inst) | otherwise = empty +pprInstInFull inst@(EqInst {}) = pprInst inst pprInstInFull inst = sep [quotes (pprInst inst), nest 2 (pprInstArising inst)] tidyInst :: TidyEnv -> Inst -> Inst +tidyInst env eq@(EqInst {tci_left = lty, tci_right = rty, tci_co = co}) = + eq { tci_left = tidyType env lty + , tci_right = tidyType env rty + , tci_co = either Left (Right . tidyType env) co + } tidyInst env lit@(LitInst {tci_ty = ty}) = lit {tci_ty = tidyType env ty} tidyInst env dict@(Dict {tci_pred = pred}) = dict {tci_pred = tidyPred env pred} tidyInst env meth@(Method {tci_tys = tys}) = meth {tci_tys = tidyTypes env tys} @@ -609,7 +682,7 @@ addLocalInst home_ie ispec -- Check for duplicate instance decls ; let { (matches, _) = lookupInstEnv inst_envs cls tys' ; dup_ispecs = [ dup_ispec - | (_, dup_ispec) <- matches + | (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. @@ -624,8 +697,8 @@ addLocalInst home_ie ispec getOverlapFlag :: TcM OverlapFlag getOverlapFlag = do { dflags <- getDOpts - ; let overlap_ok = dopt Opt_AllowOverlappingInstances dflags - incoherent_ok = dopt Opt_AllowIncoherentInstances dflags + ; let overlap_ok = dopt Opt_OverlappingInstances dflags + incoherent_ok = dopt Opt_IncoherentInstances dflags overlap_flag | incoherent_ok = Incoherent | overlap_ok = OverlapOk | otherwise = NoOverlap @@ -666,18 +739,20 @@ data LookupInstResult | GenInst [Inst] (LHsExpr TcId) -- The expression and its needed insts lookupSimpleInst :: Inst -> TcM LookupInstResult --- This is "simple" in tthat it returns NoInstance for implication constraints +-- This is "simple" in that it returns NoInstance for implication constraints -- 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 +lookupSimpleInst (EqInst {}) = return NoInstance + --------------------- Implications ------------------------ lookupSimpleInst (ImplicInst {}) = return NoInstance --------------------- Methods ------------------------ lookupSimpleInst (Method {tci_oid = id, tci_tys = tys, tci_theta = theta, tci_loc = loc}) - = do { (dicts, dict_app) <- instCallDicts loc theta + = do { (dict_app, dicts) <- getLIE $ instCallDicts loc theta ; let co_fn = dict_app <.> mkWpTyApps tys ; return (GenInst dicts (L span $ HsWrap co_fn (HsVar id))) } where @@ -714,24 +789,25 @@ lookupSimpleInst (LitInst {tci_lit = HsFractional f from_rat_name, tci_ty = ty, returnM (GenInst [method_inst] (mkHsApp (L (instLocSpan loc) (HsVar (instToId method_inst))) rat_lit)) +lookupSimpleInst (LitInst {tci_lit = HsIsString s from_string_name, tci_ty = ty, tci_loc = loc}) + | Just expr <- shortCutStringLit s ty + = returnM (GenInst [] (noLoc expr)) + | otherwise + = ASSERT( from_string_name `isHsVar` fromStringName ) -- A LitInst invariant + tcLookupId fromStringName `thenM` \ from_string -> + tcInstClassOp loc from_string [ty] `thenM` \ method_inst -> + mkStrLit s `thenM` \ string_lit -> + returnM (GenInst [method_inst] + (mkHsApp (L (instLocSpan loc) + (HsVar (instToId method_inst))) string_lit)) + --------------------- Dictionaries ------------------------ lookupSimpleInst (Dict {tci_pred = pred, tci_loc = 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 + Just (dfun_id, mb_inst_tys) -> do + { use_stage <- getStage ; checkWellStaged (ptext SLIT("instance for") <+> quotes (ppr pred)) (topIdLvl dfun_id) use_stage @@ -740,36 +816,32 @@ lookupSimpleInst (Dict {tci_pred = pred, tci_loc = loc}) -- 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 + -- Hence mb_inst_tys :: Either TyVar TcType + + ; let inst_tv (Left tv) = do { tv' <- tcInstTyVar tv; return (mkTyVarTy tv') } + inst_tv (Right ty) = return ty + ; tys <- mappM inst_tv mb_inst_tys ; 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 + (theta, _) = tcSplitPhiTy (applyTys (idType dfun_id) tys) src_loc = instLocSpan loc dfun = HsVar dfun_id - tys = map (substTyVar tenv') tyvars ; if null theta then returnM (GenInst [] (L src_loc $ HsWrap (mkWpTyApps tys) dfun)) else do - { (dicts, dict_app) <- instCallDicts loc theta + { (dict_app, dicts) <- getLIE $ instCallDicts loc theta -- !!! ; let co_fn = dict_app <.> mkWpTyApps tys ; returnM (GenInst dicts (L src_loc $ HsWrap co_fn dfun)) }}}} --------------- -lookupPred :: TcPredType -> TcM (Maybe (TvSubst, DFunId)) +lookupPred :: TcPredType -> TcM (Maybe (DFunId, [Either TyVar TcType])) -- 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)], []) + ([(ispec, inst_tys)], []) -> do { let dfun_id = is_dfun ispec ; traceTc (text "lookupInst success" <+> vcat [text "dict" <+> ppr pred, @@ -777,7 +849,7 @@ lookupPred pred@(ClassP clas tys) <+> ppr (idType dfun_id) ]) -- Record that this dfun is needed ; record_dfun_usage dfun_id - ; return (Just (tenv, dfun_id)) } ; + ; return (Just (dfun_id, inst_tys)) } ; (matches, unifs) -> do { traceTc (text "lookupInst fail" <+> @@ -885,3 +957,92 @@ syntaxNameCtxt name orig ty tidy_env in returnM (tidy_env, msg) \end{code} + +%************************************************************************ +%* * + EqInsts +%* * +%************************************************************************ + +\begin{code} +mkGivenCo :: Coercion -> Either TcTyVar Coercion +mkGivenCo = Right + +mkWantedCo :: TcTyVar -> Either TcTyVar Coercion +mkWantedCo = Left + +fromGivenCo :: Either TcTyVar Coercion -> Coercion +fromGivenCo (Right co) = co +fromGivenCo _ = panic "fromGivenCo: not a wanted coercion" + +fromWantedCo :: String -> Either TcTyVar Coercion -> TcTyVar +fromWantedCo _ (Left covar) = covar +fromWantedCo msg _ = panic ("fromWantedCo: not a wanted coercion: " ++ msg) + +eitherEqInst :: Inst -- given or wanted EqInst + -> (TcTyVar -> a) -- result if wanted + -> (Coercion -> a) -- result if given + -> a +eitherEqInst (EqInst {tci_co = either_co}) withWanted withGiven + = case either_co of + Left covar -> withWanted covar + Right co -> withGiven co + +mkEqInsts :: [PredType] -> [Either TcTyVar Coercion] -> TcM [Inst] +mkEqInsts preds cos = zipWithM mkEqInst preds cos + +mkEqInst :: PredType -> Either TcTyVar Coercion -> TcM Inst +mkEqInst (EqPred ty1 ty2) co + = do { uniq <- newUnique + ; src_span <- getSrcSpanM + ; err_ctxt <- getErrCtxt + ; let loc = InstLoc EqOrigin src_span err_ctxt + name = mkName uniq src_span + inst = EqInst {tci_left = ty1, tci_right = ty2, tci_co = co, tci_loc = loc, tci_name = name} + ; return inst + } + where mkName uniq src_span = mkInternalName uniq (mkVarOcc "co") src_span + +mkWantedEqInst :: PredType -> TcM Inst +mkWantedEqInst pred@(EqPred ty1 ty2) + = do { cotv <- newMetaTyVar TauTv (mkCoKind ty1 ty2) + ; mkEqInst pred (Left cotv) + } + +-- type inference: +-- We want to promote the wanted EqInst to a given EqInst +-- in the signature context. +-- This means we have to give the coercion a name +-- and fill it in as its own name. +finalizeEqInst + :: Inst -- wanted + -> TcM Inst -- given +finalizeEqInst wanted@(EqInst {tci_left = ty1, tci_right = ty2, tci_name = name}) + = do { let var = Var.mkCoVar name (PredTy $ EqPred ty1 ty2) + ; writeWantedCoercion wanted (TyVarTy var) + ; let given = wanted { tci_co = mkGivenCo $ TyVarTy var } + ; return given + } + +writeWantedCoercion + :: Inst -- wanted EqInst + -> Coercion -- coercion to fill the hole with + -> TcM () +writeWantedCoercion wanted co + = do { let cotv = fromWantedCo "writeWantedCoercion" $ tci_co wanted + ; writeMetaTyVar cotv co + } + +eqInstType :: Inst -> TcType +eqInstType inst = eitherEqInst inst mkTyVarTy id + +eqInstCoercion :: Inst -> Either TcTyVar Coercion +eqInstCoercion = tci_co + +eqInstLeftTy, eqInstRightTy :: Inst -> TcType +eqInstLeftTy = tci_left +eqInstRightTy = tci_right + +updateEqInstCoercion :: (Either TcTyVar Coercion -> Either TcTyVar Coercion) -> Inst -> Inst +updateEqInstCoercion f inst = inst {tci_co = f $ tci_co inst} +\end{code}