{- (c) The University of Glasgow 2006 (c) The GRASP/AQUA Project, Glasgow University, 1992-1998 Monadic type operations This module contains monadic operations over types that contain mutable type variables -} {-# LANGUAGE CPP, TupleSections, MultiWayIf #-} module TcMType ( TcTyVar, TcKind, TcType, TcTauType, TcThetaType, TcTyVarSet, -------------------------------- -- Creating new mutable type variables newFlexiTyVar, newFlexiTyVarTy, -- Kind -> TcM TcType newFlexiTyVarTys, -- Int -> Kind -> TcM [TcType] newOpenFlexiTyVarTy, newOpenTypeKind, newMetaKindVar, newMetaKindVars, newMetaTyVarTyAtLevel, cloneMetaTyVar, newFmvTyVar, newFskTyVar, readMetaTyVar, writeMetaTyVar, newMetaDetails, isFilledMetaTyVar, isUnfilledMetaTyVar, -------------------------------- -- Expected types ExpType(..), ExpSigmaType, ExpRhoType, mkCheckExpType, newInferExpType, newInferExpTypeInst, newInferExpTypeNoInst, readExpType, readExpType_maybe, expTypeToType, checkingExpType_maybe, checkingExpType, tauifyExpType, inferResultToType, -------------------------------- -- Creating fresh type variables for pm checking genInstSkolTyVarsX, -------------------------------- -- Creating new evidence variables newEvVar, newEvVars, newDict, newWanted, newWanteds, cloneWanted, cloneWC, emitWanted, emitWantedEq, emitWantedEvVar, emitWantedEvVars, newTcEvBinds, addTcEvBind, newCoercionHole, fillCoercionHole, isFilledCoercionHole, unpackCoercionHole, unpackCoercionHole_maybe, checkCoercionHole, -------------------------------- -- Instantiation newMetaTyVars, newMetaTyVarX, newMetaTyVarsX, newMetaSigTyVars, newMetaSigTyVarX, newSigTyVar, newWildCardX, tcInstType, tcInstSkolTyVars,tcInstSkolTyVarsX, tcInstSuperSkolTyVarsX, tcSkolDFunType, tcSuperSkolTyVars, instSkolTyCoVars, freshenTyVarBndrs, freshenCoVarBndrsX, -------------------------------- -- Zonking and tidying zonkTidyTcType, zonkTidyOrigin, tidyEvVar, tidyCt, tidySkolemInfo, skolemiseRuntimeUnk, zonkTcTyVar, zonkTcTyVars, zonkTcTyVarToTyVar, zonkSigTyVarPairs, zonkTyCoVarsAndFV, zonkTcTypeAndFV, zonkTyCoVarsAndFVList, zonkTcTypeAndSplitDepVars, zonkTcTypesAndSplitDepVars, zonkQuantifiedTyVar, defaultTyVar, quantifyTyVars, zonkTcTyCoVarBndr, zonkTcTyVarBinder, zonkTcType, zonkTcTypes, zonkCo, zonkTyCoVarKind, zonkTcTypeMapper, zonkEvVar, zonkWC, zonkSimples, zonkId, zonkCoVar, zonkCt, zonkSkolemInfo, tcGetGlobalTyCoVars, ------------------------------ -- Levity polymorphism ensureNotLevPoly, checkForLevPoly, checkForLevPolyX, formatLevPolyErr ) where #include "HsVersions.h" -- friends: import GhcPrelude import TyCoRep import TcType import Type import Kind import Coercion import Class import Var -- others: import TcRnMonad -- TcType, amongst others import TcEvidence import Id import Name import VarSet import TysWiredIn import TysPrim import VarEnv import NameEnv import PrelNames import Util import Outputable import FastString import SrcLoc import Bag import Pair import UniqSet import qualified GHC.LanguageExtensions as LangExt import Control.Monad import Maybes import Data.List ( mapAccumL ) import Control.Arrow ( second ) {- ************************************************************************ * * Kind variables * * ************************************************************************ -} mkKindName :: Unique -> Name mkKindName unique = mkSystemName unique kind_var_occ kind_var_occ :: OccName -- Just one for all MetaKindVars -- They may be jiggled by tidying kind_var_occ = mkOccName tvName "k" newMetaKindVar :: TcM TcKind newMetaKindVar = do { uniq <- newUnique ; details <- newMetaDetails TauTv ; let kv = mkTcTyVar (mkKindName uniq) liftedTypeKind details ; return (mkTyVarTy kv) } newMetaKindVars :: Int -> TcM [TcKind] newMetaKindVars n = mapM (\ _ -> newMetaKindVar) (nOfThem n ()) {- ************************************************************************ * * Evidence variables; range over constraints we can abstract over * * ************************************************************************ -} newEvVars :: TcThetaType -> TcM [EvVar] newEvVars theta = mapM newEvVar theta -------------- newEvVar :: TcPredType -> TcRnIf gbl lcl EvVar -- Creates new *rigid* variables for predicates newEvVar ty = do { name <- newSysName (predTypeOccName ty) ; return (mkLocalIdOrCoVar name ty) } newWanted :: CtOrigin -> Maybe TypeOrKind -> PredType -> TcM CtEvidence -- Deals with both equality and non-equality predicates newWanted orig t_or_k pty = do loc <- getCtLocM orig t_or_k d <- if isEqPred pty then HoleDest <$> newCoercionHole pty else EvVarDest <$> newEvVar pty return $ CtWanted { ctev_dest = d , ctev_pred = pty , ctev_nosh = WDeriv , ctev_loc = loc } newWanteds :: CtOrigin -> ThetaType -> TcM [CtEvidence] newWanteds orig = mapM (newWanted orig Nothing) cloneWanted :: Ct -> TcM CtEvidence cloneWanted ct = newWanted (ctEvOrigin ev) Nothing (ctEvPred ev) where ev = ctEvidence ct cloneWC :: WantedConstraints -> TcM WantedConstraints cloneWC wc@(WC { wc_simple = simples, wc_impl = implics }) = do { simples' <- mapBagM clone_one simples ; implics' <- mapBagM clone_implic implics ; return (wc { wc_simple = simples', wc_impl = implics' }) } where clone_one ct = do { ev <- cloneWanted ct; return (mkNonCanonical ev) } clone_implic implic@(Implic { ic_wanted = inner_wanted }) = do { inner_wanted' <- cloneWC inner_wanted ; return (implic { ic_wanted = inner_wanted' }) } -- | Emits a new Wanted. Deals with both equalities and non-equalities. emitWanted :: CtOrigin -> TcPredType -> TcM EvTerm emitWanted origin pty = do { ev <- newWanted origin Nothing pty ; emitSimple $ mkNonCanonical ev ; return $ ctEvTerm ev } -- | Emits a new equality constraint emitWantedEq :: CtOrigin -> TypeOrKind -> Role -> TcType -> TcType -> TcM Coercion emitWantedEq origin t_or_k role ty1 ty2 = do { hole <- newCoercionHole pty ; loc <- getCtLocM origin (Just t_or_k) ; emitSimple $ mkNonCanonical $ CtWanted { ctev_pred = pty, ctev_dest = HoleDest hole , ctev_nosh = WDeriv, ctev_loc = loc } ; return (HoleCo hole) } where pty = mkPrimEqPredRole role ty1 ty2 -- | Creates a new EvVar and immediately emits it as a Wanted. -- No equality predicates here. emitWantedEvVar :: CtOrigin -> TcPredType -> TcM EvVar emitWantedEvVar origin ty = do { new_cv <- newEvVar ty ; loc <- getCtLocM origin Nothing ; let ctev = CtWanted { ctev_dest = EvVarDest new_cv , ctev_pred = ty , ctev_nosh = WDeriv , ctev_loc = loc } ; emitSimple $ mkNonCanonical ctev ; return new_cv } emitWantedEvVars :: CtOrigin -> [TcPredType] -> TcM [EvVar] emitWantedEvVars orig = mapM (emitWantedEvVar orig) newDict :: Class -> [TcType] -> TcM DictId newDict cls tys = do { name <- newSysName (mkDictOcc (getOccName cls)) ; return (mkLocalId name (mkClassPred cls tys)) } predTypeOccName :: PredType -> OccName predTypeOccName ty = case classifyPredType ty of ClassPred cls _ -> mkDictOcc (getOccName cls) EqPred _ _ _ -> mkVarOccFS (fsLit "co") IrredPred _ -> mkVarOccFS (fsLit "irred") {- ************************************************************************ * * Coercion holes * * ************************************************************************ -} newCoercionHole :: TcPredType -> TcM CoercionHole newCoercionHole pred_ty = do { co_var <- newEvVar pred_ty ; traceTc "New coercion hole:" (ppr co_var) ; ref <- newMutVar Nothing ; return $ CoercionHole { ch_co_var = co_var, ch_ref = ref } } -- | Put a value in a coercion hole fillCoercionHole :: CoercionHole -> Coercion -> TcM () fillCoercionHole (CoercionHole { ch_ref = ref, ch_co_var = cv }) co = do { #if defined(DEBUG) ; cts <- readTcRef ref ; whenIsJust cts $ \old_co -> pprPanic "Filling a filled coercion hole" (ppr cv $$ ppr co $$ ppr old_co) #endif ; traceTc "Filling coercion hole" (ppr cv <+> text ":=" <+> ppr co) ; writeTcRef ref (Just co) } -- | Is a coercion hole filled in? isFilledCoercionHole :: CoercionHole -> TcM Bool isFilledCoercionHole (CoercionHole { ch_ref = ref }) = isJust <$> readTcRef ref -- | Retrieve the contents of a coercion hole. Panics if the hole -- is unfilled unpackCoercionHole :: CoercionHole -> TcM Coercion unpackCoercionHole hole = do { contents <- unpackCoercionHole_maybe hole ; case contents of Just co -> return co Nothing -> pprPanic "Unfilled coercion hole" (ppr hole) } -- | Retrieve the contents of a coercion hole, if it is filled unpackCoercionHole_maybe :: CoercionHole -> TcM (Maybe Coercion) unpackCoercionHole_maybe (CoercionHole { ch_ref = ref }) = readTcRef ref -- | Check that a coercion is appropriate for filling a hole. (The hole -- itself is needed only for printing. NB: This must be /lazy/ in the coercion, -- as it's used in TcHsSyn in the presence of knots. -- Always returns the checked coercion, but this return value is necessary -- so that the input coercion is forced only when the output is forced. checkCoercionHole :: CoVar -> Coercion -> TcM Coercion checkCoercionHole cv co | debugIsOn = do { cv_ty <- zonkTcType (varType cv) -- co is already zonked, but cv might not be ; return $ ASSERT2( ok cv_ty , (text "Bad coercion hole" <+> ppr cv <> colon <+> vcat [ ppr t1, ppr t2, ppr role , ppr cv_ty ]) ) co } | otherwise = return co where (Pair t1 t2, role) = coercionKindRole co ok cv_ty | EqPred cv_rel cv_t1 cv_t2 <- classifyPredType cv_ty = t1 `eqType` cv_t1 && t2 `eqType` cv_t2 && role == eqRelRole cv_rel | otherwise = False {- ************************************************************************ * Expected types * ************************************************************************ Note [ExpType] ~~~~~~~~~~~~~~ An ExpType is used as the "expected type" when type-checking an expression. An ExpType can hold a "hole" that can be filled in by the type-checker. This allows us to have one tcExpr that works in both checking mode and synthesis mode (that is, bidirectional type-checking). Previously, this was achieved by using ordinary unification variables, but we don't need or want that generality. (For example, #11397 was caused by doing the wrong thing with unification variables.) Instead, we observe that these holes should 1. never be nested 2. never appear as the type of a variable 3. be used linearly (never be duplicated) By defining ExpType, separately from Type, we can achieve goals 1 and 2 statically. See also [wiki:Typechecking] Note [TcLevel of ExpType] ~~~~~~~~~~~~~~~~~~~~~~~~~ Consider data G a where MkG :: G Bool foo MkG = True This is a classic untouchable-variable / ambiguous GADT return type scenario. But, with ExpTypes, we'll be inferring the type of the RHS. And, because there is only one branch of the case, we won't trigger Note [Case branches must never infer a non-tau type] of TcMatches. We thus must track a TcLevel in an Inferring ExpType. If we try to fill the ExpType and find that the TcLevels don't work out, we fill the ExpType with a tau-tv at the low TcLevel, hopefully to be worked out later by some means. This is triggered in test gadt/gadt-escape1. -} -- actual data definition is in TcType -- | Make an 'ExpType' suitable for inferring a type of kind * or #. newInferExpTypeNoInst :: TcM ExpSigmaType newInferExpTypeNoInst = newInferExpType False newInferExpTypeInst :: TcM ExpRhoType newInferExpTypeInst = newInferExpType True newInferExpType :: Bool -> TcM ExpType newInferExpType inst = do { u <- newUnique ; tclvl <- getTcLevel ; traceTc "newOpenInferExpType" (ppr u <+> ppr inst <+> ppr tclvl) ; ref <- newMutVar Nothing ; return (Infer (IR { ir_uniq = u, ir_lvl = tclvl , ir_ref = ref, ir_inst = inst })) } -- | Extract a type out of an ExpType, if one exists. But one should always -- exist. Unless you're quite sure you know what you're doing. readExpType_maybe :: ExpType -> TcM (Maybe TcType) readExpType_maybe (Check ty) = return (Just ty) readExpType_maybe (Infer (IR { ir_ref = ref})) = readMutVar ref -- | Extract a type out of an ExpType. Otherwise, panics. readExpType :: ExpType -> TcM TcType readExpType exp_ty = do { mb_ty <- readExpType_maybe exp_ty ; case mb_ty of Just ty -> return ty Nothing -> pprPanic "Unknown expected type" (ppr exp_ty) } -- | Returns the expected type when in checking mode. checkingExpType_maybe :: ExpType -> Maybe TcType checkingExpType_maybe (Check ty) = Just ty checkingExpType_maybe _ = Nothing -- | Returns the expected type when in checking mode. Panics if in inference -- mode. checkingExpType :: String -> ExpType -> TcType checkingExpType _ (Check ty) = ty checkingExpType err et = pprPanic "checkingExpType" (text err $$ ppr et) tauifyExpType :: ExpType -> TcM ExpType -- ^ Turn a (Infer hole) type into a (Check alpha), -- where alpha is a fresh unification variable tauifyExpType (Check ty) = return (Check ty) -- No-op for (Check ty) tauifyExpType (Infer inf_res) = do { ty <- inferResultToType inf_res ; return (Check ty) } -- | Extracts the expected type if there is one, or generates a new -- TauTv if there isn't. expTypeToType :: ExpType -> TcM TcType expTypeToType (Check ty) = return ty expTypeToType (Infer inf_res) = inferResultToType inf_res inferResultToType :: InferResult -> TcM Type inferResultToType (IR { ir_uniq = u, ir_lvl = tc_lvl , ir_ref = ref }) = do { rr <- newMetaTyVarTyAtLevel tc_lvl runtimeRepTy ; tau <- newMetaTyVarTyAtLevel tc_lvl (tYPE rr) -- See Note [TcLevel of ExpType] ; writeMutVar ref (Just tau) ; traceTc "Forcing ExpType to be monomorphic:" (ppr u <+> text ":=" <+> ppr tau) ; return tau } {- ********************************************************************* * * SkolemTvs (immutable) * * ********************************************************************* -} tcInstType :: ([TyVar] -> TcM (TCvSubst, [TcTyVar])) -- ^ How to instantiate the type variables -> Id -- ^ Type to instantiate -> TcM ([(Name, TcTyVar)], TcThetaType, TcType) -- ^ Result -- (type vars, preds (incl equalities), rho) tcInstType inst_tyvars id = case tcSplitForAllTys (idType id) of ([], rho) -> let -- There may be overloading despite no type variables; -- (?x :: Int) => Int -> Int (theta, tau) = tcSplitPhiTy rho in return ([], theta, tau) (tyvars, rho) -> do { (subst, tyvars') <- inst_tyvars tyvars ; let (theta, tau) = tcSplitPhiTy (substTyAddInScope subst rho) tv_prs = map tyVarName tyvars `zip` tyvars' ; return (tv_prs, theta, tau) } tcSkolDFunType :: DFunId -> TcM ([TcTyVar], TcThetaType, TcType) -- Instantiate a type signature with skolem constants. -- We could give them fresh names, but no need to do so tcSkolDFunType dfun = do { (tv_prs, theta, tau) <- tcInstType tcInstSuperSkolTyVars dfun ; return (map snd tv_prs, theta, tau) } tcSuperSkolTyVars :: [TyVar] -> (TCvSubst, [TcTyVar]) -- Make skolem constants, but do *not* give them new names, as above -- Moreover, make them "super skolems"; see comments with superSkolemTv -- see Note [Kind substitution when instantiating] -- Precondition: tyvars should be ordered by scoping tcSuperSkolTyVars = mapAccumL tcSuperSkolTyVar emptyTCvSubst tcSuperSkolTyVar :: TCvSubst -> TyVar -> (TCvSubst, TcTyVar) tcSuperSkolTyVar subst tv = (extendTvSubstWithClone subst tv new_tv, new_tv) where kind = substTyUnchecked subst (tyVarKind tv) new_tv = mkTcTyVar (tyVarName tv) kind superSkolemTv -- | Given a list of @['TyVar']@, skolemize the type variables, -- returning a substitution mapping the original tyvars to the -- skolems, and the list of newly bound skolems. See also -- tcInstSkolTyVars' for a precondition. The resulting -- skolems are non-overlappable; see Note [Overlap and deriving] -- for an example where this matters. tcInstSkolTyVars :: [TyVar] -> TcM (TCvSubst, [TcTyVar]) tcInstSkolTyVars = tcInstSkolTyVarsX emptyTCvSubst tcInstSkolTyVarsX :: TCvSubst -> [TyVar] -> TcM (TCvSubst, [TcTyVar]) tcInstSkolTyVarsX = tcInstSkolTyVars' False tcInstSuperSkolTyVars :: [TyVar] -> TcM (TCvSubst, [TcTyVar]) tcInstSuperSkolTyVars = tcInstSuperSkolTyVarsX emptyTCvSubst tcInstSuperSkolTyVarsX :: TCvSubst -> [TyVar] -> TcM (TCvSubst, [TcTyVar]) tcInstSuperSkolTyVarsX subst = tcInstSkolTyVars' True subst tcInstSkolTyVars' :: Bool -> TCvSubst -> [TyVar] -> TcM (TCvSubst, [TcTyVar]) -- Precondition: tyvars should be ordered (kind vars first) -- see Note [Kind substitution when instantiating] -- Get the location from the monad; this is a complete freshening operation tcInstSkolTyVars' overlappable subst tvs = do { loc <- getSrcSpanM ; lvl <- getTcLevel ; instSkolTyCoVarsX (mkTcSkolTyVar lvl loc overlappable) subst tvs } mkTcSkolTyVar :: TcLevel -> SrcSpan -> Bool -> TcTyCoVarMaker gbl lcl mkTcSkolTyVar lvl loc overlappable old_name kind = do { uniq <- newUnique ; let name = mkInternalName uniq (getOccName old_name) loc ; return (mkTcTyVar name kind details) } where details = SkolemTv (pushTcLevel lvl) overlappable -- NB: skolems bump the level ------------------ freshenTyVarBndrs :: [TyVar] -> TcRnIf gbl lcl (TCvSubst, [TyVar]) -- ^ Give fresh uniques to a bunch of TyVars, but they stay -- as TyVars, rather than becoming TcTyVars -- Used in FamInst.newFamInst, and Inst.newClsInst freshenTyVarBndrs = instSkolTyCoVars mk_tv where mk_tv old_name kind = do { uniq <- newUnique ; return (mkTyVar (setNameUnique old_name uniq) kind) } freshenCoVarBndrsX :: TCvSubst -> [CoVar] -> TcRnIf gbl lcl (TCvSubst, [CoVar]) -- ^ Give fresh uniques to a bunch of CoVars -- Used in FamInst.newFamInst freshenCoVarBndrsX subst = instSkolTyCoVarsX mk_cv subst where mk_cv old_name kind = do { uniq <- newUnique ; return (mkCoVar (setNameUnique old_name uniq) kind) } ------------------ type TcTyCoVarMaker gbl lcl = Name -> Kind -> TcRnIf gbl lcl TyCoVar -- The TcTyCoVarMaker should make a fresh Name, based on the old one -- Freshness is critical. See Note [Skolems in zonkSyntaxExpr] in TcHsSyn instSkolTyCoVars :: TcTyCoVarMaker gbl lcl -> [TyVar] -> TcRnIf gbl lcl (TCvSubst, [TyCoVar]) instSkolTyCoVars mk_tcv = instSkolTyCoVarsX mk_tcv emptyTCvSubst instSkolTyCoVarsX :: TcTyCoVarMaker gbl lcl -> TCvSubst -> [TyCoVar] -> TcRnIf gbl lcl (TCvSubst, [TyCoVar]) instSkolTyCoVarsX mk_tcv = mapAccumLM (instSkolTyCoVarX mk_tcv) instSkolTyCoVarX :: TcTyCoVarMaker gbl lcl -> TCvSubst -> TyCoVar -> TcRnIf gbl lcl (TCvSubst, TyCoVar) instSkolTyCoVarX mk_tcv subst tycovar = do { new_tcv <- mk_tcv old_name kind ; let subst1 | isTyVar new_tcv = extendTvSubstWithClone subst tycovar new_tcv | otherwise = extendCvSubstWithClone subst tycovar new_tcv ; return (subst1, new_tcv) } where old_name = tyVarName tycovar kind = substTyUnchecked subst (tyVarKind tycovar) newFskTyVar :: TcType -> TcM TcTyVar newFskTyVar fam_ty = do { uniq <- newUnique ; ref <- newMutVar Flexi ; let details = MetaTv { mtv_info = FlatSkolTv , mtv_ref = ref , mtv_tclvl = fmvTcLevel } name = mkMetaTyVarName uniq (fsLit "fsk") ; return (mkTcTyVar name (typeKind fam_ty) details) } {- Note [Kind substitution when instantiating] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ When we instantiate a bunch of kind and type variables, first we expect them to be topologically sorted. Then we have to instantiate the kind variables, build a substitution from old variables to the new variables, then instantiate the type variables substituting the original kind. Exemple: If we want to instantiate [(k1 :: *), (k2 :: *), (a :: k1 -> k2), (b :: k1)] we want [(?k1 :: *), (?k2 :: *), (?a :: ?k1 -> ?k2), (?b :: ?k1)] instead of the buggous [(?k1 :: *), (?k2 :: *), (?a :: k1 -> k2), (?b :: k1)] ************************************************************************ * * MetaTvs (meta type variables; mutable) * * ************************************************************************ -} newSigTyVar :: Name -> Kind -> TcM TcTyVar newSigTyVar name kind = do { details <- newMetaDetails SigTv ; return (mkTcTyVar name kind details) } newFmvTyVar :: TcType -> TcM TcTyVar -- Very like newMetaTyVar, except sets mtv_tclvl to one less -- so that the fmv is untouchable. newFmvTyVar fam_ty = do { uniq <- newUnique ; ref <- newMutVar Flexi ; let details = MetaTv { mtv_info = FlatMetaTv , mtv_ref = ref , mtv_tclvl = fmvTcLevel } name = mkMetaTyVarName uniq (fsLit "s") ; return (mkTcTyVar name (typeKind fam_ty) details) } newMetaDetails :: MetaInfo -> TcM TcTyVarDetails newMetaDetails info = do { ref <- newMutVar Flexi ; tclvl <- getTcLevel ; return (MetaTv { mtv_info = info , mtv_ref = ref , mtv_tclvl = tclvl }) } cloneMetaTyVar :: TcTyVar -> TcM TcTyVar cloneMetaTyVar tv = ASSERT( isTcTyVar tv ) do { uniq <- newUnique ; ref <- newMutVar Flexi ; let name' = setNameUnique (tyVarName tv) uniq details' = case tcTyVarDetails tv of details@(MetaTv {}) -> details { mtv_ref = ref } _ -> pprPanic "cloneMetaTyVar" (ppr tv) ; return (mkTcTyVar name' (tyVarKind tv) details') } -- Works for both type and kind variables readMetaTyVar :: TyVar -> TcM MetaDetails readMetaTyVar tyvar = ASSERT2( isMetaTyVar tyvar, ppr tyvar ) readMutVar (metaTyVarRef tyvar) isFilledMetaTyVar :: TyVar -> TcM Bool -- True of a filled-in (Indirect) meta type variable isFilledMetaTyVar tv | MetaTv { mtv_ref = ref } <- tcTyVarDetails tv = do { details <- readMutVar ref ; return (isIndirect details) } | otherwise = return False isUnfilledMetaTyVar :: TyVar -> TcM Bool -- True of a un-filled-in (Flexi) meta type variable isUnfilledMetaTyVar tv | MetaTv { mtv_ref = ref } <- tcTyVarDetails tv = do { details <- readMutVar ref ; return (isFlexi details) } | otherwise = return False -------------------- -- Works with both type and kind variables writeMetaTyVar :: TcTyVar -> TcType -> TcM () -- Write into a currently-empty MetaTyVar writeMetaTyVar tyvar ty | not debugIsOn = writeMetaTyVarRef tyvar (metaTyVarRef tyvar) ty -- Everything from here on only happens if DEBUG is on | not (isTcTyVar tyvar) = WARN( True, text "Writing to non-tc tyvar" <+> ppr tyvar ) return () | MetaTv { mtv_ref = ref } <- tcTyVarDetails tyvar = writeMetaTyVarRef tyvar ref ty | otherwise = WARN( True, text "Writing to non-meta tyvar" <+> ppr tyvar ) return () -------------------- writeMetaTyVarRef :: TcTyVar -> TcRef MetaDetails -> TcType -> TcM () -- Here the tyvar is for error checking only; -- the ref cell must be for the same tyvar writeMetaTyVarRef tyvar ref ty | not debugIsOn = do { traceTc "writeMetaTyVar" (ppr tyvar <+> dcolon <+> ppr (tyVarKind tyvar) <+> text ":=" <+> ppr ty) ; writeTcRef ref (Indirect ty) } -- Everything from here on only happens if DEBUG is on | otherwise = do { meta_details <- readMutVar ref; -- Zonk kinds to allow the error check to work ; zonked_tv_kind <- zonkTcType tv_kind ; zonked_ty_kind <- zonkTcType ty_kind ; let kind_check_ok = isPredTy tv_kind -- Don't check kinds for updates -- to coercion variables. Why not?? || isConstraintKind zonked_tv_kind || tcEqKind zonked_ty_kind zonked_tv_kind -- Hack alert! isConstraintKind: see TcHsType -- Note [Extra-constraint holes in partial type signatures] kind_msg = hang (text "Ill-kinded update to meta tyvar") 2 ( ppr tyvar <+> text "::" <+> (ppr tv_kind $$ ppr zonked_tv_kind) <+> text ":=" <+> ppr ty <+> text "::" <+> (ppr ty_kind $$ ppr zonked_ty_kind) ) ; traceTc "writeMetaTyVar" (ppr tyvar <+> text ":=" <+> ppr ty) -- Check for double updates ; MASSERT2( isFlexi meta_details, double_upd_msg meta_details ) -- Check for level OK -- See Note [Level check when unifying] ; MASSERT2( level_check_ok, level_check_msg ) -- Check Kinds ok ; MASSERT2( kind_check_ok, kind_msg ) -- Do the write ; writeMutVar ref (Indirect ty) } where tv_kind = tyVarKind tyvar ty_kind = typeKind ty tv_lvl = tcTyVarLevel tyvar ty_lvl = tcTypeLevel ty level_check_ok = isFlattenTyVar tyvar || not (ty_lvl `strictlyDeeperThan` tv_lvl) level_check_msg = ppr ty_lvl $$ ppr tv_lvl $$ ppr tyvar $$ ppr ty double_upd_msg details = hang (text "Double update of meta tyvar") 2 (ppr tyvar $$ ppr details) {- Note [Level check when unifying] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ When unifying alpha:lvl := ty we expect that the TcLevel of 'ty' will be <= lvl. However, during unflatting we do fuv:l := ty:(l+1) which is usually wrong; hence the check isFmmvTyVar in level_check_ok. See Note [TcLevel assignment] in TcType. -} {- % Generating fresh variables for pattern match check -} -- UNINSTANTIATED VERSION OF tcInstSkolTyCoVars genInstSkolTyVarsX :: SrcSpan -> TCvSubst -> [TyVar] -> TcRnIf gbl lcl (TCvSubst, [TcTyVar]) -- Precondition: tyvars should be scoping-ordered -- see Note [Kind substitution when instantiating] -- Get the location from the monad; this is a complete freshening operation genInstSkolTyVarsX loc subst tvs = instSkolTyCoVarsX (mkTcSkolTyVar topTcLevel loc False) subst tvs {- ************************************************************************ * * MetaTvs: TauTvs * * ************************************************************************ Note [Never need to instantiate coercion variables] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ With coercion variables sloshing around in types, it might seem that we sometimes need to instantiate coercion variables. This would be problematic, because coercion variables inhabit unboxed equality (~#), and the constraint solver thinks in terms only of boxed equality (~). The solution is that we never need to instantiate coercion variables in the first place. The tyvars that we need to instantiate come from the types of functions, data constructors, and patterns. These will never be quantified over coercion variables, except for the special case of the promoted Eq#. But, that can't ever appear in user code, so we're safe! -} mkMetaTyVarName :: Unique -> FastString -> Name -- Makes a /System/ Name, which is eagerly eliminated by -- the unifier; see TcUnify.nicer_to_update_tv1, and -- TcCanonical.canEqTyVarTyVar (nicer_to_update_tv2) mkMetaTyVarName uniq str = mkSystemName uniq (mkTyVarOccFS str) newAnonMetaTyVar :: MetaInfo -> Kind -> TcM TcTyVar -- Make a new meta tyvar out of thin air newAnonMetaTyVar meta_info kind = do { uniq <- newUnique ; let name = mkMetaTyVarName uniq s s = case meta_info of TauTv -> fsLit "t" FlatMetaTv -> fsLit "fmv" FlatSkolTv -> fsLit "fsk" SigTv -> fsLit "a" ; details <- newMetaDetails meta_info ; return (mkTcTyVar name kind details) } cloneAnonMetaTyVar :: MetaInfo -> TyVar -> TcKind -> TcM TcTyVar -- Same as newAnonMetaTyVar, but use a supplied TyVar as the source of the print-name cloneAnonMetaTyVar info tv kind = do { uniq <- newUnique ; details <- newMetaDetails info ; let name = mkSystemName uniq (getOccName tv) -- See Note [Name of an instantiated type variable] ; return (mkTcTyVar name kind details) } {- Note [Name of an instantiated type variable] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ At the moment we give a unification variable a System Name, which influences the way it is tidied; see TypeRep.tidyTyVarBndr. -} newFlexiTyVar :: Kind -> TcM TcTyVar newFlexiTyVar kind = newAnonMetaTyVar TauTv kind newFlexiTyVarTy :: Kind -> TcM TcType newFlexiTyVarTy kind = do tc_tyvar <- newFlexiTyVar kind return (mkTyVarTy tc_tyvar) newFlexiTyVarTys :: Int -> Kind -> TcM [TcType] newFlexiTyVarTys n kind = mapM newFlexiTyVarTy (nOfThem n kind) newOpenTypeKind :: TcM TcKind newOpenTypeKind = do { rr <- newFlexiTyVarTy runtimeRepTy ; return (tYPE rr) } -- | Create a tyvar that can be a lifted or unlifted type. -- Returns alpha :: TYPE kappa, where both alpha and kappa are fresh newOpenFlexiTyVarTy :: TcM TcType newOpenFlexiTyVarTy = do { kind <- newOpenTypeKind ; newFlexiTyVarTy kind } newMetaSigTyVars :: [TyVar] -> TcM (TCvSubst, [TcTyVar]) newMetaSigTyVars = mapAccumLM newMetaSigTyVarX emptyTCvSubst newMetaTyVars :: [TyVar] -> TcM (TCvSubst, [TcTyVar]) -- Instantiate with META type variables -- Note that this works for a sequence of kind, type, and coercion variables -- variables. Eg [ (k:*), (a:k->k) ] -- Gives [ (k7:*), (a8:k7->k7) ] newMetaTyVars = mapAccumLM newMetaTyVarX emptyTCvSubst -- emptyTCvSubst has an empty in-scope set, but that's fine here -- Since the tyvars are freshly made, they cannot possibly be -- captured by any existing for-alls. newMetaTyVarX :: TCvSubst -> TyVar -> TcM (TCvSubst, TcTyVar) -- Make a new unification variable tyvar whose Name and Kind come from -- an existing TyVar. We substitute kind variables in the kind. newMetaTyVarX subst tyvar = new_meta_tv_x TauTv subst tyvar newMetaTyVarsX :: TCvSubst -> [TyVar] -> TcM (TCvSubst, [TcTyVar]) -- Just like newMetaTyVars, but start with an existing substitution. newMetaTyVarsX subst = mapAccumLM newMetaTyVarX subst newMetaSigTyVarX :: TCvSubst -> TyVar -> TcM (TCvSubst, TcTyVar) -- Just like newMetaTyVarX, but make a SigTv newMetaSigTyVarX subst tyvar = new_meta_tv_x SigTv subst tyvar newWildCardX :: TCvSubst -> TyVar -> TcM (TCvSubst, TcTyVar) newWildCardX subst tv = do { new_tv <- newAnonMetaTyVar TauTv (substTy subst (tyVarKind tv)) ; return (extendTvSubstWithClone subst tv new_tv, new_tv) } new_meta_tv_x :: MetaInfo -> TCvSubst -> TyVar -> TcM (TCvSubst, TcTyVar) new_meta_tv_x info subst tv = do { new_tv <- cloneAnonMetaTyVar info tv substd_kind ; let subst1 = extendTvSubstWithClone subst tv new_tv ; return (subst1, new_tv) } where substd_kind = substTyUnchecked subst (tyVarKind tv) -- NOTE: Trac #12549 is fixed so we could use -- substTy here, but the tc_infer_args problem -- is not yet fixed so leaving as unchecked for now. -- OLD NOTE: -- Unchecked because we call newMetaTyVarX from -- tcInstBinder, which is called from tc_infer_args -- which does not yet take enough trouble to ensure -- the in-scope set is right; e.g. Trac #12785 trips -- if we use substTy here newMetaTyVarTyAtLevel :: TcLevel -> TcKind -> TcM TcType newMetaTyVarTyAtLevel tc_lvl kind = do { uniq <- newUnique ; ref <- newMutVar Flexi ; let name = mkMetaTyVarName uniq (fsLit "p") details = MetaTv { mtv_info = TauTv , mtv_ref = ref , mtv_tclvl = tc_lvl } ; return (mkTyVarTy (mkTcTyVar name kind details)) } {- ********************************************************************* * * Quantification * * ************************************************************************ Note [quantifyTyVars] ~~~~~~~~~~~~~~~~~~~~~ quantifyTyVars is given the free vars of a type that we are about to wrap in a forall. It takes these free type/kind variables (partitioned into dependent and non-dependent variables) and 1. Zonks them and remove globals and covars 2. Extends kvs1 with free kind vars in the kinds of tvs (removing globals) 3. Calls zonkQuantifiedTyVar on each Step (2) is often unimportant, because the kind variable is often also free in the type. Eg Typeable k (a::k) has free vars {k,a}. But the type (see Trac #7916) (f::k->*) (a::k) has free vars {f,a}, but we must add 'k' as well! Hence step (3). * This function distinguishes between dependent and non-dependent variables only to keep correct defaulting behavior with -XNoPolyKinds. With -XPolyKinds, it treats both classes of variables identically. * quantifyTyVars never quantifies over - a coercion variable - a runtime-rep variable Note [quantifyTyVars determinism] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The results of quantifyTyVars are wrapped in a forall and can end up in the interface file. One such example is inferred type signatures. They also affect the results of optimizations, for example worker-wrapper. This means that to get deterministic builds quantifyTyVars needs to be deterministic. To achieve this CandidatesQTvs is backed by deterministic sets which allows them to be later converted to a list in a deterministic order. For more information about deterministic sets see Note [Deterministic UniqFM] in UniqDFM. -} quantifyTyVars :: TcTyCoVarSet -- Global tvs; already zonked -> CandidatesQTvs -- See Note [Dependent type variables] in TcType -- Already zonked -> TcM [TcTyVar] -- See Note [quantifyTyVars] -- Can be given a mixture of TcTyVars and TyVars, in the case of -- associated type declarations. Also accepts covars, but *never* returns any. quantifyTyVars gbl_tvs dvs@(DV{ dv_kvs = dep_tkvs, dv_tvs = nondep_tkvs }) = do { traceTc "quantifyTyVars" (vcat [ppr dvs, ppr gbl_tvs]) ; let dep_kvs = dVarSetElemsWellScoped $ dep_tkvs `dVarSetMinusVarSet` gbl_tvs -- dVarSetElemsWellScoped: put the kind variables into -- well-scoped order. -- E.g. [k, (a::k)] not the other way roud nondep_tvs = dVarSetElems $ (nondep_tkvs `minusDVarSet` dep_tkvs) `dVarSetMinusVarSet` gbl_tvs -- See Note [Dependent type variables] in TcType -- The `minus` dep_tkvs removes any kind-level vars -- e.g. T k (a::k) Since k appear in a kind it'll -- be in dv_kvs, and is dependent. So remove it from -- dv_tvs which will also contain k -- No worry about dependent covars here; -- they are all in dep_tkvs -- No worry about scoping, because these are all -- type variables -- NB kinds of tvs are zonked by zonkTyCoVarsAndFV -- In the non-PolyKinds case, default the kind variables -- to *, and zonk the tyvars as usual. Notice that this -- may make quantifyTyVars return a shorter list -- than it was passed, but that's ok ; poly_kinds <- xoptM LangExt.PolyKinds ; dep_kvs' <- mapMaybeM (zonk_quant (not poly_kinds)) dep_kvs ; nondep_tvs' <- mapMaybeM (zonk_quant False) nondep_tvs ; let final_qtvs = dep_kvs' ++ nondep_tvs' -- Because of the order, any kind variables -- mentioned in the kinds of the nondep_tvs' -- now refer to the dep_kvs' ; traceTc "quantifyTyVars" (vcat [ text "globals:" <+> ppr gbl_tvs , text "nondep:" <+> pprTyVars nondep_tvs , text "dep:" <+> pprTyVars dep_kvs , text "dep_kvs'" <+> pprTyVars dep_kvs' , text "nondep_tvs'" <+> pprTyVars nondep_tvs' ]) -- We should never quantify over coercion variables; check this ; let co_vars = filter isCoVar final_qtvs ; MASSERT2( null co_vars, ppr co_vars ) ; return final_qtvs } where -- zonk_quant returns a tyvar if it should be quantified over; -- otherwise, it returns Nothing. The latter case happens for -- * Kind variables, with -XNoPolyKinds: don't quantify over these -- * RuntimeRep variables: we never quantify over these zonk_quant default_kind tkv | not (isTcTyVar tkv) = return (Just tkv) -- For associated types, we have the class variables -- in scope, and they are TyVars not TcTyVars | otherwise = do { deflt_done <- defaultTyVar default_kind tkv ; case deflt_done of True -> return Nothing False -> do { tv <- zonkQuantifiedTyVar tkv ; return (Just tv) } } zonkQuantifiedTyVar :: TcTyVar -> TcM TcTyVar -- The quantified type variables often include meta type variables -- we want to freeze them into ordinary type variables -- The meta tyvar is updated to point to the new skolem TyVar. Now any -- bound occurrences of the original type variable will get zonked to -- the immutable version. -- -- We leave skolem TyVars alone; they are immutable. -- -- This function is called on both kind and type variables, -- but kind variables *only* if PolyKinds is on. zonkQuantifiedTyVar tv = case tcTyVarDetails tv of SkolemTv {} -> do { kind <- zonkTcType (tyVarKind tv) ; return (setTyVarKind tv kind) } -- It might be a skolem type variable, -- for example from a user type signature MetaTv {} -> skolemiseUnboundMetaTyVar tv _other -> pprPanic "zonkQuantifiedTyVar" (ppr tv) -- RuntimeUnk defaultTyVar :: Bool -- True <=> please default this kind variable to * -> TcTyVar -- If it's a MetaTyVar then it is unbound -> TcM Bool -- True <=> defaulted away altogether defaultTyVar default_kind tv | not (isMetaTyVar tv) = return False | isSigTyVar tv -- Do not default SigTvs. Doing so would violate the invariants -- on SigTvs; see Note [Signature skolems] in TcType. -- Trac #13343 is an example; #14555 is another -- See Note [Kind generalisation and SigTvs] = return False | isRuntimeRepVar tv -- Do not quantify over a RuntimeRep var -- unless it is a SigTv, handled earlier = do { traceTc "Defaulting a RuntimeRep var to LiftedRep" (ppr tv) ; writeMetaTyVar tv liftedRepTy ; return True } | default_kind -- -XNoPolyKinds and this is a kind var = do { default_kind_var tv -- so default it to * if possible ; return True } | otherwise = return False where default_kind_var :: TyVar -> TcM () -- defaultKindVar is used exclusively with -XNoPolyKinds -- See Note [Defaulting with -XNoPolyKinds] -- It takes an (unconstrained) meta tyvar and defaults it. -- Works only on vars of type *; for other kinds, it issues an error. default_kind_var kv | isStarKind (tyVarKind kv) = do { traceTc "Defaulting a kind var to *" (ppr kv) ; writeMetaTyVar kv liftedTypeKind } | otherwise = addErr (vcat [ text "Cannot default kind variable" <+> quotes (ppr kv') , text "of kind:" <+> ppr (tyVarKind kv') , text "Perhaps enable PolyKinds or add a kind signature" ]) where (_, kv') = tidyOpenTyCoVar emptyTidyEnv kv skolemiseRuntimeUnk :: TcTyVar -> TcM TyVar skolemiseRuntimeUnk tv = skolemise_tv tv RuntimeUnk skolemiseUnboundMetaTyVar :: TcTyVar -> TcM TyVar skolemiseUnboundMetaTyVar tv = skolemise_tv tv (SkolemTv (metaTyVarTcLevel tv) False) skolemise_tv :: TcTyVar -> TcTyVarDetails -> TcM TyVar -- We have a Meta tyvar with a ref-cell inside it -- Skolemise it, so that -- we are totally out of Meta-tyvar-land -- We create a skolem TyVar, not a regular TyVar -- See Note [Zonking to Skolem] skolemise_tv tv details = ASSERT2( isMetaTyVar tv, ppr tv ) do { when debugIsOn (check_empty tv) ; span <- getSrcSpanM -- Get the location from "here" -- ie where we are generalising ; kind <- zonkTcType (tyVarKind tv) ; let uniq = getUnique tv -- NB: Use same Unique as original tyvar. This is -- important for TcHsType.splitTelescopeTvs to work properly tv_name = getOccName tv final_name = mkInternalName uniq tv_name span final_tv = mkTcTyVar final_name kind details ; traceTc "Skolemising" (ppr tv <+> text ":=" <+> ppr final_tv) ; writeMetaTyVar tv (mkTyVarTy final_tv) ; return final_tv } where check_empty tv -- [Sept 04] Check for non-empty. = when debugIsOn $ -- See note [Silly Type Synonym] do { cts <- readMetaTyVar tv ; case cts of Flexi -> return () Indirect ty -> WARN( True, ppr tv $$ ppr ty ) return () } {- Note [Defaulting with -XNoPolyKinds] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Consider data Compose f g a = Mk (f (g a)) We infer Compose :: forall k1 k2. (k2 -> *) -> (k1 -> k2) -> k1 -> * Mk :: forall k1 k2 (f :: k2 -> *) (g :: k1 -> k2) (a :: k1). f (g a) -> Compose k1 k2 f g a Now, in another module, we have -XNoPolyKinds -XDataKinds in effect. What does 'Mk mean? Pre GHC-8.0 with -XNoPolyKinds, we just defaulted all kind variables to *. But that's no good here, because the kind variables in 'Mk aren't of kind *, so defaulting to * is ill-kinded. After some debate on #11334, we decided to issue an error in this case. The code is in defaultKindVar. Note [What is a meta variable?] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ A "meta type-variable", also know as a "unification variable" is a placeholder introduced by the typechecker for an as-yet-unknown monotype. For example, when we see a call `reverse (f xs)`, we know that we calling reverse :: forall a. [a] -> [a] So we know that the argument `f xs` must be a "list of something". But what is the "something"? We don't know until we explore the `f xs` a bit more. So we set out what we do know at the call of `reverse` by instantiate its type with a fresh meta tyvar, `alpha` say. So now the type of the argument `f xs`, and of the result, is `[alpha]`. The unification variable `alpha` stands for the as-yet-unknown type of the elements of the list. As type inference progresses we may learn more about `alpha`. For example, suppose `f` has the type f :: forall b. b -> [Maybe b] Then we instantiate `f`'s type with another fresh unification variable, say `beta`; and equate `f`'s result type with reverse's argument type, thus `[alpha] ~ [Maybe beta]`. Now we can solve this equality to learn that `alpha ~ Maybe beta`, so we've refined our knowledge about `alpha`. And so on. If you found this Note useful, you may also want to have a look at Section 5 of "Practical type inference for higher rank types" (Peyton Jones, Vytiniotis, Weirich and Shields. J. Functional Programming. 2011). Note [What is zonking?] ~~~~~~~~~~~~~~~~~~~~~~~ GHC relies heavily on mutability in the typechecker for efficient operation. For this reason, throughout much of the type checking process meta type variables (the MetaTv constructor of TcTyVarDetails) are represented by mutable variables (known as TcRefs). Zonking is the process of ripping out these mutable variables and replacing them with a real Type. This involves traversing the entire type expression, but the interesting part of replacing the mutable variables occurs in zonkTyVarOcc. There are two ways to zonk a Type: * zonkTcTypeToType, which is intended to be used at the end of type-checking for the final zonk. It has to deal with unfilled metavars, either by filling it with a value like Any or failing (determined by the UnboundTyVarZonker used). * zonkTcType, which will happily ignore unfilled metavars. This is the appropriate function to use while in the middle of type-checking. Note [Zonking to Skolem] ~~~~~~~~~~~~~~~~~~~~~~~~ We used to zonk quantified type variables to regular TyVars. However, this leads to problems. Consider this program from the regression test suite: eval :: Int -> String -> String -> String eval 0 root actual = evalRHS 0 root actual evalRHS :: Int -> a evalRHS 0 root actual = eval 0 root actual It leads to the deferral of an equality (wrapped in an implication constraint) forall a. () => ((String -> String -> String) ~ a) which is propagated up to the toplevel (see TcSimplify.tcSimplifyInferCheck). In the meantime `a' is zonked and quantified to form `evalRHS's signature. This has the *side effect* of also zonking the `a' in the deferred equality (which at this point is being handed around wrapped in an implication constraint). Finally, the equality (with the zonked `a') will be handed back to the simplifier by TcRnDriver.tcRnSrcDecls calling TcSimplify.tcSimplifyTop. If we zonk `a' with a regular type variable, we will have this regular type variable now floating around in the simplifier, which in many places assumes to only see proper TcTyVars. We can avoid this problem by zonking with a skolem. The skolem is rigid (which we require for a quantified variable), but is still a TcTyVar that the simplifier knows how to deal with. Note [Silly Type Synonyms] ~~~~~~~~~~~~~~~~~~~~~~~~~~ Consider this: type C u a = u -- Note 'a' unused foo :: (forall a. C u a -> C u a) -> u foo x = ... bar :: Num u => u bar = foo (\t -> t + t) * From the (\t -> t+t) we get type {Num d} => d -> d where d is fresh. * Now unify with type of foo's arg, and we get: {Num (C d a)} => C d a -> C d a where a is fresh. * Now abstract over the 'a', but float out the Num (C d a) constraint because it does not 'really' mention a. (see exactTyVarsOfType) The arg to foo becomes \/\a -> \t -> t+t * So we get a dict binding for Num (C d a), which is zonked to give a = () [Note Sept 04: now that we are zonking quantified type variables on construction, the 'a' will be frozen as a regular tyvar on quantification, so the floated dict will still have type (C d a). Which renders this whole note moot; happily!] * Then the \/\a abstraction has a zonked 'a' in it. All very silly. I think its harmless to ignore the problem. We'll end up with a \/\a in the final result but all the occurrences of a will be zonked to () ************************************************************************ * * Zonking types * * ************************************************************************ -} -- | @tcGetGlobalTyCoVars@ returns a fully-zonked set of *scoped* tyvars free in -- the environment. To improve subsequent calls to the same function it writes -- the zonked set back into the environment. Note that this returns all -- variables free in anything (term-level or type-level) in scope. We thus -- don't have to worry about clashes with things that are not in scope, because -- if they are reachable, then they'll be returned here. tcGetGlobalTyCoVars :: TcM TcTyVarSet tcGetGlobalTyCoVars = do { (TcLclEnv {tcl_tyvars = gtv_var}) <- getLclEnv ; gbl_tvs <- readMutVar gtv_var ; gbl_tvs' <- zonkTyCoVarsAndFV gbl_tvs ; writeMutVar gtv_var gbl_tvs' ; return gbl_tvs' } -- | Zonk a type without using the smart constructors; the result type -- is available for inspection within the type-checking knot. zonkTcTypeInKnot :: TcType -> TcM TcType zonkTcTypeInKnot = mapType (zonkTcTypeMapper { tcm_smart = False }) () zonkTcTypeAndFV :: TcType -> TcM DTyCoVarSet -- Zonk a type and take its free variables -- With kind polymorphism it can be essential to zonk *first* -- so that we find the right set of free variables. Eg -- forall k1. forall (a:k2). a -- where k2:=k1 is in the substitution. We don't want -- k2 to look free in this type! -- NB: This might be called from within the knot, so don't use -- smart constructors. See Note [Type-checking inside the knot] in TcHsType zonkTcTypeAndFV ty = tyCoVarsOfTypeDSet <$> zonkTcTypeInKnot ty -- | Zonk a type and call 'candidateQTyVarsOfType' on it. -- Works within the knot. zonkTcTypeAndSplitDepVars :: TcType -> TcM CandidatesQTvs zonkTcTypeAndSplitDepVars ty = candidateQTyVarsOfType <$> zonkTcTypeInKnot ty zonkTcTypesAndSplitDepVars :: [TcType] -> TcM CandidatesQTvs zonkTcTypesAndSplitDepVars tys = candidateQTyVarsOfTypes <$> mapM zonkTcTypeInKnot tys zonkTyCoVar :: TyCoVar -> TcM TcType -- Works on TyVars and TcTyVars zonkTyCoVar tv | isTcTyVar tv = zonkTcTyVar tv | isTyVar tv = mkTyVarTy <$> zonkTyCoVarKind tv | otherwise = ASSERT2( isCoVar tv, ppr tv ) mkCoercionTy . mkCoVarCo <$> zonkTyCoVarKind tv -- Hackily, when typechecking type and class decls -- we have TyVars in scopeadded (only) in -- TcHsType.tcTyClTyVars, but it seems -- painful to make them into TcTyVars there zonkTyCoVarsAndFV :: TyCoVarSet -> TcM TyCoVarSet zonkTyCoVarsAndFV tycovars = tyCoVarsOfTypes <$> mapM zonkTyCoVar (nonDetEltsUniqSet tycovars) -- It's OK to use nonDetEltsUniqSet here because we immediately forget about -- the ordering by turning it into a nondeterministic set and the order -- of zonking doesn't matter for determinism. -- Takes a list of TyCoVars, zonks them and returns a -- deterministically ordered list of their free variables. zonkTyCoVarsAndFVList :: [TyCoVar] -> TcM [TyCoVar] zonkTyCoVarsAndFVList tycovars = tyCoVarsOfTypesList <$> mapM zonkTyCoVar tycovars zonkTcTyVars :: [TcTyVar] -> TcM [TcType] zonkTcTyVars tyvars = mapM zonkTcTyVar tyvars ----------------- Types zonkTyCoVarKind :: TyCoVar -> TcM TyCoVar zonkTyCoVarKind tv = do { kind' <- zonkTcType (tyVarKind tv) ; return (setTyVarKind tv kind') } zonkTcTypes :: [TcType] -> TcM [TcType] zonkTcTypes tys = mapM zonkTcType tys {- ************************************************************************ * * Zonking constraints * * ************************************************************************ -} zonkImplication :: Implication -> TcM Implication zonkImplication implic@(Implic { ic_skols = skols , ic_given = given , ic_wanted = wanted , ic_info = info }) = do { skols' <- mapM zonkTcTyCoVarBndr skols -- Need to zonk their kinds! -- as Trac #7230 showed ; given' <- mapM zonkEvVar given ; info' <- zonkSkolemInfo info ; wanted' <- zonkWCRec wanted ; return (implic { ic_skols = skols' , ic_given = given' , ic_wanted = wanted' , ic_info = info' }) } zonkEvVar :: EvVar -> TcM EvVar zonkEvVar var = do { ty' <- zonkTcType (varType var) ; return (setVarType var ty') } zonkWC :: WantedConstraints -> TcM WantedConstraints zonkWC wc = zonkWCRec wc zonkWCRec :: WantedConstraints -> TcM WantedConstraints zonkWCRec (WC { wc_simple = simple, wc_impl = implic }) = do { simple' <- zonkSimples simple ; implic' <- mapBagM zonkImplication implic ; return (WC { wc_simple = simple', wc_impl = implic' }) } zonkSimples :: Cts -> TcM Cts zonkSimples cts = do { cts' <- mapBagM zonkCt' cts ; traceTc "zonkSimples done:" (ppr cts') ; return cts' } zonkCt' :: Ct -> TcM Ct zonkCt' ct = zonkCt ct {- Note [zonkCt behaviour] ~~~~~~~~~~~~~~~~~~~~~~~~~~ zonkCt tries to maintain the canonical form of a Ct. For example, - a CDictCan should stay a CDictCan; - a CTyEqCan should stay a CTyEqCan (if the LHS stays as a variable.). - a CHoleCan should stay a CHoleCan - a CIrredCan should stay a CIrredCan with its cc_insol flag intact Why?, for example: - For CDictCan, the @TcSimplify.expandSuperClasses@ step, which runs after the simple wanted and plugin loop, looks for @CDictCan@s. If a plugin is in use, constraints are zonked before being passed to the plugin. This means if we don't preserve a canonical form, @expandSuperClasses@ fails to expand superclasses. This is what happened in Trac #11525. - For CHoleCan, once we forget that it's a hole, we can never recover that info. - For CIrredCan we want to see if a constraint is insoluble with insolubleWC NB: we do not expect to see any CFunEqCans, because zonkCt is only called on unflattened constraints. NB: Constraints are always re-flattened etc by the canonicaliser in @TcCanonical@ even if they come in as CDictCan. Only canonical constraints that are actually in the inert set carry all the guarantees. So it is okay if zonkCt creates e.g. a CDictCan where the cc_tyars are /not/ function free. -} zonkCt :: Ct -> TcM Ct zonkCt ct@(CHoleCan { cc_ev = ev }) = do { ev' <- zonkCtEvidence ev ; return $ ct { cc_ev = ev' } } zonkCt ct@(CDictCan { cc_ev = ev, cc_tyargs = args }) = do { ev' <- zonkCtEvidence ev ; args' <- mapM zonkTcType args ; return $ ct { cc_ev = ev', cc_tyargs = args' } } zonkCt ct@(CTyEqCan { cc_ev = ev, cc_tyvar = tv, cc_rhs = rhs }) = do { ev' <- zonkCtEvidence ev ; tv_ty' <- zonkTcTyVar tv ; case getTyVar_maybe tv_ty' of Just tv' -> do { rhs' <- zonkTcType rhs ; return ct { cc_ev = ev' , cc_tyvar = tv' , cc_rhs = rhs' } } Nothing -> return (mkNonCanonical ev') } zonkCt ct@(CIrredCan { cc_ev = ev }) -- Preserve the cc_insol flag = do { ev' <- zonkCtEvidence ev ; return (ct { cc_ev = ev' }) } zonkCt ct = ASSERT( not (isCFunEqCan ct) ) -- We do not expect to see any CFunEqCans, because zonkCt is only called on -- unflattened constraints. do { fl' <- zonkCtEvidence (cc_ev ct) ; return (mkNonCanonical fl') } zonkCtEvidence :: CtEvidence -> TcM CtEvidence zonkCtEvidence ctev@(CtGiven { ctev_pred = pred }) = do { pred' <- zonkTcType pred ; return (ctev { ctev_pred = pred'}) } zonkCtEvidence ctev@(CtWanted { ctev_pred = pred, ctev_dest = dest }) = do { pred' <- zonkTcType pred ; let dest' = case dest of EvVarDest ev -> EvVarDest $ setVarType ev pred' -- necessary in simplifyInfer HoleDest h -> HoleDest h ; return (ctev { ctev_pred = pred', ctev_dest = dest' }) } zonkCtEvidence ctev@(CtDerived { ctev_pred = pred }) = do { pred' <- zonkTcType pred ; return (ctev { ctev_pred = pred' }) } zonkSkolemInfo :: SkolemInfo -> TcM SkolemInfo zonkSkolemInfo (SigSkol cx ty tv_prs) = do { ty' <- zonkTcType ty ; return (SigSkol cx ty' tv_prs) } zonkSkolemInfo (InferSkol ntys) = do { ntys' <- mapM do_one ntys ; return (InferSkol ntys') } where do_one (n, ty) = do { ty' <- zonkTcType ty; return (n, ty') } zonkSkolemInfo skol_info = return skol_info {- %************************************************************************ %* * \subsection{Zonking -- the main work-horses: zonkTcType, zonkTcTyVar} * * * For internal use only! * * * ************************************************************************ -} -- zonkId is used *during* typechecking just to zonk the Id's type zonkId :: TcId -> TcM TcId zonkId id = do { ty' <- zonkTcType (idType id) ; return (Id.setIdType id ty') } zonkCoVar :: CoVar -> TcM CoVar zonkCoVar = zonkId -- | A suitable TyCoMapper for zonking a type inside the knot, and -- before all metavars are filled in. zonkTcTypeMapper :: TyCoMapper () TcM zonkTcTypeMapper = TyCoMapper { tcm_smart = True , tcm_tyvar = const zonkTcTyVar , tcm_covar = const (\cv -> mkCoVarCo <$> zonkTyCoVarKind cv) , tcm_hole = hole , tcm_tybinder = \_env tv _vis -> ((), ) <$> zonkTcTyCoVarBndr tv } where hole :: () -> CoercionHole -> TcM Coercion hole _ hole@(CoercionHole { ch_ref = ref, ch_co_var = cv }) = do { contents <- readTcRef ref ; case contents of Just co -> do { co' <- zonkCo co ; checkCoercionHole cv co' } Nothing -> do { cv' <- zonkCoVar cv ; return $ HoleCo (hole { ch_co_var = cv' }) } } -- For unbound, mutable tyvars, zonkType uses the function given to it -- For tyvars bound at a for-all, zonkType zonks them to an immutable -- type variable and zonks the kind too zonkTcType :: TcType -> TcM TcType zonkTcType = mapType zonkTcTypeMapper () -- | "Zonk" a coercion -- really, just zonk any types in the coercion zonkCo :: Coercion -> TcM Coercion zonkCo = mapCoercion zonkTcTypeMapper () zonkTcTyCoVarBndr :: TcTyCoVar -> TcM TcTyCoVar -- A tyvar binder is never a unification variable (MetaTv), -- rather it is always a skolems. BUT it may have a kind -- that has not yet been zonked, and may include kind -- unification variables. zonkTcTyCoVarBndr tyvar -- can't use isCoVar, because it looks at a TyCon. Argh. = ASSERT2( isImmutableTyVar tyvar || (not $ isTyVar tyvar), pprTyVar tyvar ) updateTyVarKindM zonkTcType tyvar zonkTcTyVarBinder :: TyVarBndr TcTyVar vis -> TcM (TyVarBndr TcTyVar vis) zonkTcTyVarBinder (TvBndr tv vis) = do { tv' <- zonkTcTyCoVarBndr tv ; return (TvBndr tv' vis) } zonkTcTyVar :: TcTyVar -> TcM TcType -- Simply look through all Flexis zonkTcTyVar tv | isTcTyVar tv = case tcTyVarDetails tv of SkolemTv {} -> zonk_kind_and_return RuntimeUnk {} -> zonk_kind_and_return MetaTv { mtv_ref = ref } -> do { cts <- readMutVar ref ; case cts of Flexi -> zonk_kind_and_return Indirect ty -> zonkTcType ty } | otherwise -- coercion variable = zonk_kind_and_return where zonk_kind_and_return = do { z_tv <- zonkTyCoVarKind tv ; return (mkTyVarTy z_tv) } -- Variant that assumes that any result of zonking is still a TyVar. -- Should be used only on skolems and SigTvs zonkTcTyVarToTyVar :: TcTyVar -> TcM TcTyVar zonkTcTyVarToTyVar tv = do { ty <- zonkTcTyVar tv ; return (tcGetTyVar "zonkTcTyVarToVar" ty) } zonkSigTyVarPairs :: [(Name,TcTyVar)] -> TcM [(Name,TcTyVar)] zonkSigTyVarPairs prs = mapM do_one prs where do_one (nm, tv) = do { tv' <- zonkTcTyVarToTyVar tv ; return (nm, tv') } {- %************************************************************************ %* * Tidying * * ************************************************************************ -} zonkTidyTcType :: TidyEnv -> TcType -> TcM (TidyEnv, TcType) zonkTidyTcType env ty = do { ty' <- zonkTcType ty ; return (tidyOpenType env ty') } zonkTidyOrigin :: TidyEnv -> CtOrigin -> TcM (TidyEnv, CtOrigin) zonkTidyOrigin env (GivenOrigin skol_info) = do { skol_info1 <- zonkSkolemInfo skol_info ; let skol_info2 = tidySkolemInfo env skol_info1 ; return (env, GivenOrigin skol_info2) } zonkTidyOrigin env orig@(TypeEqOrigin { uo_actual = act , uo_expected = exp }) = do { (env1, act') <- zonkTidyTcType env act ; (env2, exp') <- zonkTidyTcType env1 exp ; return ( env2, orig { uo_actual = act' , uo_expected = exp' }) } zonkTidyOrigin env (KindEqOrigin ty1 m_ty2 orig t_or_k) = do { (env1, ty1') <- zonkTidyTcType env ty1 ; (env2, m_ty2') <- case m_ty2 of Just ty2 -> second Just <$> zonkTidyTcType env1 ty2 Nothing -> return (env1, Nothing) ; (env3, orig') <- zonkTidyOrigin env2 orig ; return (env3, KindEqOrigin ty1' m_ty2' orig' t_or_k) } zonkTidyOrigin env (FunDepOrigin1 p1 l1 p2 l2) = do { (env1, p1') <- zonkTidyTcType env p1 ; (env2, p2') <- zonkTidyTcType env1 p2 ; return (env2, FunDepOrigin1 p1' l1 p2' l2) } zonkTidyOrigin env (FunDepOrigin2 p1 o1 p2 l2) = do { (env1, p1') <- zonkTidyTcType env p1 ; (env2, p2') <- zonkTidyTcType env1 p2 ; (env3, o1') <- zonkTidyOrigin env2 o1 ; return (env3, FunDepOrigin2 p1' o1' p2' l2) } zonkTidyOrigin env orig = return (env, orig) ---------------- tidyCt :: TidyEnv -> Ct -> Ct -- Used only in error reporting -- Also converts it to non-canonical tidyCt env ct = case ct of CHoleCan { cc_ev = ev } -> ct { cc_ev = tidy_ev env ev } _ -> mkNonCanonical (tidy_ev env (ctEvidence ct)) where tidy_ev :: TidyEnv -> CtEvidence -> CtEvidence -- NB: we do not tidy the ctev_evar field because we don't -- show it in error messages tidy_ev env ctev@(CtGiven { ctev_pred = pred }) = ctev { ctev_pred = tidyType env pred } tidy_ev env ctev@(CtWanted { ctev_pred = pred }) = ctev { ctev_pred = tidyType env pred } tidy_ev env ctev@(CtDerived { ctev_pred = pred }) = ctev { ctev_pred = tidyType env pred } ---------------- tidyEvVar :: TidyEnv -> EvVar -> EvVar tidyEvVar env var = setVarType var (tidyType env (varType var)) ---------------- tidySkolemInfo :: TidyEnv -> SkolemInfo -> SkolemInfo tidySkolemInfo env (DerivSkol ty) = DerivSkol (tidyType env ty) tidySkolemInfo env (SigSkol cx ty tv_prs) = tidySigSkol env cx ty tv_prs tidySkolemInfo env (InferSkol ids) = InferSkol (mapSnd (tidyType env) ids) tidySkolemInfo env (UnifyForAllSkol ty) = UnifyForAllSkol (tidyType env ty) tidySkolemInfo _ info = info tidySigSkol :: TidyEnv -> UserTypeCtxt -> TcType -> [(Name,TcTyVar)] -> SkolemInfo -- We need to take special care when tidying SigSkol -- See Note [SigSkol SkolemInfo] in TcRnTypes tidySigSkol env cx ty tv_prs = SigSkol cx (tidy_ty env ty) tv_prs' where tv_prs' = mapSnd (tidyTyVarOcc env) tv_prs inst_env = mkNameEnv tv_prs' tidy_ty env (ForAllTy (TvBndr tv vis) ty) = ForAllTy (TvBndr tv' vis) (tidy_ty env' ty) where (env', tv') = tidy_tv_bndr env tv tidy_ty env (FunTy arg res) = FunTy (tidyType env arg) (tidy_ty env res) tidy_ty env ty = tidyType env ty tidy_tv_bndr :: TidyEnv -> TyVar -> (TidyEnv, TyVar) tidy_tv_bndr env@(occ_env, subst) tv | Just tv' <- lookupNameEnv inst_env (tyVarName tv) = ((occ_env, extendVarEnv subst tv tv'), tv') | otherwise = tidyTyCoVarBndr env tv ------------------------------------------------------------------------- {- %************************************************************************ %* * Levity polymorphism checks * * ************************************************************************ See Note [Levity polymorphism checking] in DsMonad -} -- | According to the rules around representation polymorphism -- (see https://ghc.haskell.org/trac/ghc/wiki/NoSubKinds), no binder -- can have a representation-polymorphic type. This check ensures -- that we respect this rule. It is a bit regrettable that this error -- occurs in zonking, after which we should have reported all errors. -- But it's hard to see where else to do it, because this can be discovered -- only after all solving is done. And, perhaps most importantly, this -- isn't really a compositional property of a type system, so it's -- not a terrible surprise that the check has to go in an awkward spot. ensureNotLevPoly :: Type -- its zonked type -> SDoc -- where this happened -> TcM () ensureNotLevPoly ty doc = whenNoErrs $ -- sometimes we end up zonking bogus definitions of type -- forall a. a. See, for example, test ghci/scripts/T9140 checkForLevPoly doc ty -- See Note [Levity polymorphism checking] in DsMonad checkForLevPoly :: SDoc -> Type -> TcM () checkForLevPoly = checkForLevPolyX addErr checkForLevPolyX :: Monad m => (SDoc -> m ()) -- how to report an error -> SDoc -> Type -> m () checkForLevPolyX add_err extra ty | isTypeLevPoly ty = add_err (formatLevPolyErr ty $$ extra) | otherwise = return () formatLevPolyErr :: Type -- levity-polymorphic type -> SDoc formatLevPolyErr ty = hang (text "A levity-polymorphic type is not allowed here:") 2 (vcat [ text "Type:" <+> ppr tidy_ty , text "Kind:" <+> ppr tidy_ki ]) where (tidy_env, tidy_ty) = tidyOpenType emptyTidyEnv ty tidy_ki = tidyType tidy_env (typeKind ty)