newFmvTyVar, newFskTyVar,
readMetaTyVar, writeMetaTyVar, writeMetaTyVarRef,
- newMetaDetails, isFilledMetaTyVar, isUnfilledMetaTyVar,
+ newMetaDetails, isFilledMetaTyVar_maybe, isFilledMetaTyVar, isUnfilledMetaTyVar,
--------------------------------
-- Expected types
tauifyExpType, inferResultToType,
--------------------------------
- -- Creating fresh type variables for pm checking
- genInstSkolTyVarsX,
-
- --------------------------------
-- Creating new evidence variables
newEvVar, newEvVars, newDict,
- newWanted, newWanteds,
+ newWanted, newWanteds, newHoleCt, cloneWanted, cloneWC,
emitWanted, emitWantedEq, emitWantedEvVar, emitWantedEvVars,
- newTcEvBinds, addTcEvBind,
+ emitDerivedEqs,
+ newTcEvBinds, newNoTcEvBinds, addTcEvBind,
newCoercionHole, fillCoercionHole, isFilledCoercionHole,
unpackCoercionHole, unpackCoercionHole_maybe,
--------------------------------
-- Instantiation
- newMetaTyVars, newMetaTyVarX,
- newMetaSigTyVars, newMetaSigTyVarX,
- newSigTyVar, newWildCardX,
+ newMetaTyVars, newMetaTyVarX, newMetaTyVarsX,
+ newMetaTyVarTyVars, newMetaTyVarTyVarX,
+ newTyVarTyVar, newTauTyVar, newSkolemTyVar, newWildCardX,
tcInstType,
- tcInstSkolTyVars, tcInstSuperSkolTyVarsX,
- tcInstSigTyVars,
- tcSkolDFunType, tcSuperSkolTyVars,
+ tcInstSkolTyVars, tcInstSkolTyVarsX, tcInstSkolTyVarsAt,
+ tcSkolDFunType, tcSuperSkolTyVars, tcInstSuperSkolTyVarsX,
- instSkolTyCoVars, freshenTyVarBndrs, freshenCoVarBndrsX,
+ freshenTyVarBndrs, freshenCoVarBndrsX,
--------------------------------
-- Zonking and tidying
- zonkTidyTcType, zonkTidyOrigin,
- mkTypeErrorThing, mkTypeErrorThingArgs,
+ zonkTidyTcType, zonkTidyTcTypes, zonkTidyOrigin,
tidyEvVar, tidyCt, tidySkolemInfo,
- skolemiseUnboundMetaTyVar, skolemiseRuntimeUnk,
- zonkTcTyVar, zonkTcTyVars, zonkTcTyVarToTyVar,
+ zonkTcTyVar, zonkTcTyVars,
+ zonkTcTyVarToTyVar, zonkTyVarTyVarPairs,
zonkTyCoVarsAndFV, zonkTcTypeAndFV,
zonkTyCoVarsAndFVList,
- zonkTcTypeAndSplitDepVars, zonkTcTypesAndSplitDepVars,
- zonkQuantifiedTyVar,
- quantifyTyVars, quantifyZonkedTyVars,
- zonkTcTyCoVarBndr, zonkTcTyBinder, zonkTyConBinder,
+ candidateQTyVarsOfType, candidateQTyVarsOfKind,
+ candidateQTyVarsOfTypes, candidateQTyVarsOfKinds,
+ CandidatesQTvs(..), delCandidates, candidateKindVars,
+ skolemiseQuantifiedTyVar, defaultTyVar,
+ quantifyTyVars,
+ zonkTcTyCoVarBndr, zonkTyConBinders,
zonkTcType, zonkTcTypes, zonkCo,
- zonkTyCoVarKind, zonkTcTypeMapper,
+ zonkTyCoVarKind,
+
+ zonkEvVar, zonkWC, zonkSimples,
+ zonkId, zonkCoVar,
+ zonkCt, zonkSkolemInfo,
- zonkEvVar, zonkWC, zonkSimples, zonkId, zonkCt, zonkSkolemInfo,
+ tcGetGlobalTyCoVars,
- tcGetGlobalTyCoVars
+ ------------------------------
+ -- Levity polymorphism
+ ensureNotLevPoly, checkForLevPoly, checkForLevPolyX, formatLevPolyErr
) where
#include "HsVersions.h"
-- friends:
+import GhcPrelude
+
import TyCoRep
import TcType
import Type
-import TyCon( TyConBinder )
-import Kind
+import TyCon
import Coercion
import Class
import Var
import TysWiredIn
import TysPrim
import VarEnv
+import NameEnv
import PrelNames
import Util
import Outputable
import FastString
-import SrcLoc
import Bag
import Pair
-import UniqFM
+import UniqSet
import qualified GHC.LanguageExtensions as LangExt
import Control.Monad
import Maybes
import Data.List ( mapAccumL )
import Control.Arrow ( second )
+import qualified Data.Semigroup as Semi
{-
************************************************************************
newMetaKindVar = do { uniq <- newUnique
; details <- newMetaDetails TauTv
; let kv = mkTcTyVar (mkKindName uniq) liftedTypeKind details
+ ; traceTc "newMetaKindVar" (ppr kv)
; return (mkTyVarTy kv) }
newMetaKindVars :: Int -> TcM [TcKind]
-- 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 <$> newCoercionHole
+ d <- if isEqPred pty then HoleDest <$> 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)
+-- | Create a new 'CHoleCan' 'Ct'.
+newHoleCt :: Hole -> Id -> Type -> TcM Ct
+newHoleCt hole ev ty = do
+ loc <- getCtLocM HoleOrigin Nothing
+ pure $ CHoleCan { cc_ev = CtWanted { ctev_pred = ty
+ , ctev_dest = EvVarDest ev
+ , ctev_nosh = WDeriv
+ , ctev_loc = loc }
+ , cc_hole = hole }
+
+----------------------------------------------
+-- Cloning constraints
+----------------------------------------------
+
+cloneWanted :: Ct -> TcM Ct
+cloneWanted ct
+ | ev@(CtWanted { ctev_dest = HoleDest {}, ctev_pred = pty }) <- ctEvidence ct
+ = do { co_hole <- newCoercionHole pty
+ ; return (mkNonCanonical (ev { ctev_dest = HoleDest co_hole })) }
+ | otherwise
+ = return ct
+
+cloneWC :: WantedConstraints -> TcM WantedConstraints
+-- Clone all the evidence bindings in
+-- a) the ic_bind field of any implications
+-- b) the CoercionHoles of any wanted constraints
+-- so that solving the WantedConstraints will not have any visible side
+-- effect, /except/ from causing unifications
+cloneWC wc@(WC { wc_simple = simples, wc_impl = implics })
+ = do { simples' <- mapBagM cloneWanted simples
+ ; implics' <- mapBagM cloneImplication implics
+ ; return (wc { wc_simple = simples', wc_impl = implics' }) }
+
+cloneImplication :: Implication -> TcM Implication
+cloneImplication implic@(Implic { ic_binds = binds, ic_wanted = inner_wanted })
+ = do { binds' <- cloneEvBindsVar binds
+ ; inner_wanted' <- cloneWC inner_wanted
+ ; return (implic { ic_binds = binds', ic_wanted = inner_wanted' }) }
+
+----------------------------------------------
+-- Emitting constraints
+----------------------------------------------
+
-- | Emits a new Wanted. Deals with both equalities and non-equalities.
emitWanted :: CtOrigin -> TcPredType -> TcM EvTerm
emitWanted origin pty
; emitSimple $ mkNonCanonical ev
; return $ ctEvTerm ev }
+emitDerivedEqs :: CtOrigin -> [(TcType,TcType)] -> TcM ()
+-- Emit some new derived nominal equalities
+emitDerivedEqs origin pairs
+ | null pairs
+ = return ()
+ | otherwise
+ = do { loc <- getCtLocM origin Nothing
+ ; emitSimples (listToBag (map (mk_one loc) pairs)) }
+ where
+ mk_one loc (ty1, ty2)
+ = mkNonCanonical $
+ CtDerived { ctev_pred = mkPrimEqPred ty1 ty2
+ , ctev_loc = loc }
+
-- | Emits a new equality constraint
emitWantedEq :: CtOrigin -> TypeOrKind -> Role -> TcType -> TcType -> TcM Coercion
emitWantedEq origin t_or_k role ty1 ty2
- = do { hole <- newCoercionHole
+ = do { hole <- newCoercionHole pty
; loc <- getCtLocM origin (Just t_or_k)
; emitSimple $ mkNonCanonical $
- CtWanted { ctev_pred = pty, ctev_dest = HoleDest hole, ctev_loc = loc }
- ; return (mkHoleCo hole role ty1 ty2) }
+ CtWanted { ctev_pred = pty, ctev_dest = HoleDest hole
+ , ctev_nosh = WDeriv, ctev_loc = loc }
+ ; return (HoleCo hole) }
where
pty = mkPrimEqPredRole role ty1 ty2
; 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 }
predTypeOccName :: PredType -> OccName
predTypeOccName ty = case classifyPredType ty of
ClassPred cls _ -> mkDictOcc (getOccName cls)
- EqPred _ _ _ -> mkVarOccFS (fsLit "cobox")
- IrredPred _ -> mkVarOccFS (fsLit "irred")
+ EqPred {} -> mkVarOccFS (fsLit "co")
+ IrredPred {} -> mkVarOccFS (fsLit "irred")
+ ForAllPred {} -> mkVarOccFS (fsLit "df")
{-
************************************************************************
************************************************************************
-}
-newCoercionHole :: TcM CoercionHole
-newCoercionHole
- = do { u <- newUnique
- ; traceTc "New coercion hole:" (ppr u)
+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 u ref }
+ ; return $ CoercionHole { ch_co_var = co_var, ch_ref = ref } }
-- | Put a value in a coercion hole
fillCoercionHole :: CoercionHole -> Coercion -> TcM ()
-fillCoercionHole (CoercionHole u ref) co
+fillCoercionHole (CoercionHole { ch_ref = ref, ch_co_var = cv }) co
= do {
-#ifdef DEBUG
+#if defined(DEBUG)
; cts <- readTcRef ref
; whenIsJust cts $ \old_co ->
- pprPanic "Filling a filled coercion hole" (ppr u $$ ppr co $$ ppr old_co)
+ pprPanic "Filling a filled coercion hole" (ppr cv $$ ppr co $$ ppr old_co)
#endif
- ; traceTc "Filling coercion hole" (ppr u <+> text ":=" <+> ppr co)
+ ; 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 _ ref) = isJust <$> readTcRef ref
+isFilledCoercionHole (CoercionHole { ch_ref = ref }) = isJust <$> readTcRef ref
-- | Retrieve the contents of a coercion hole. Panics if the hole
-- is unfilled
-- | Retrieve the contents of a coercion hole, if it is filled
unpackCoercionHole_maybe :: CoercionHole -> TcM (Maybe Coercion)
-unpackCoercionHole_maybe (CoercionHole _ ref) = readTcRef ref
+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.
+-- itself is needed only for printing.
-- 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 :: Coercion -> CoercionHole -> Role -> Type -> Type -> TcM Coercion
-checkCoercionHole co h r t1 t2
--- co is already zonked, but t1 and t2 might not be
+checkCoercionHole :: CoVar -> Coercion -> TcM Coercion
+checkCoercionHole cv co
| debugIsOn
- = do { t1 <- zonkTcType t1
- ; t2 <- zonkTcType t2
- ; let (Pair _t1 _t2, _role) = coercionKindRole co
+ = do { cv_ty <- zonkTcType (varType cv)
+ -- co is already zonked, but cv might not be
; return $
- ASSERT2( t1 `eqType` _t1 && t2 `eqType` _t2 && r == _role
+ ASSERT2( ok cv_ty
, (text "Bad coercion hole" <+>
- ppr h <> colon <+> vcat [ ppr _t1, ppr _t2, ppr _role
- , ppr co, ppr t1, ppr t2
- , ppr r ]) )
+ 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
+
{-
************************************************************************
*
-- | 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.
+-- skolems, and the list of newly bound skolems.
tcInstSkolTyVars :: [TyVar] -> TcM (TCvSubst, [TcTyVar])
-tcInstSkolTyVars = tcInstSkolTyVars' False emptyTCvSubst
+-- See Note [Skolemising type variables]
+tcInstSkolTyVars = tcInstSkolTyVarsX emptyTCvSubst
+
+tcInstSkolTyVarsX :: TCvSubst -> [TyVar] -> TcM (TCvSubst, [TcTyVar])
+-- See Note [Skolemising type variables]
+tcInstSkolTyVarsX = tcInstSkolTyVarsPushLevel False
tcInstSuperSkolTyVars :: [TyVar] -> TcM (TCvSubst, [TcTyVar])
+-- See Note [Skolemising type variables]
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 -> TcTyVarMaker
-mkTcSkolTyVar lvl loc overlappable
- = \ uniq old_name kind -> mkTcTyVar (mkInternalName uniq (getOccName old_name) loc)
- kind details
+-- See Note [Skolemising type variables]
+tcInstSuperSkolTyVarsX subst = tcInstSkolTyVarsPushLevel True subst
+
+tcInstSkolTyVarsPushLevel :: Bool -> TCvSubst -> [TyVar]
+ -> TcM (TCvSubst, [TcTyVar])
+-- Skolemise one level deeper, hence pushTcLevel
+-- See Note [Skolemising type variables]
+tcInstSkolTyVarsPushLevel overlappable subst tvs
+ = do { tc_lvl <- getTcLevel
+ ; let pushed_lvl = pushTcLevel tc_lvl
+ ; tcInstSkolTyVarsAt pushed_lvl overlappable subst tvs }
+
+tcInstSkolTyVarsAt :: TcLevel -> Bool
+ -> TCvSubst -> [TyVar]
+ -> TcM (TCvSubst, [TcTyVar])
+tcInstSkolTyVarsAt lvl overlappable subst tvs
+ = freshenTyCoVarsX new_skol_tv subst tvs
where
- details = SkolemTv (pushTcLevel lvl) overlappable
- -- NB: skolems bump the level
-
-tcInstSigTyVars :: SrcSpan -> [TyVar]
- -> TcM (TCvSubst, [TcTyVar])
-tcInstSigTyVars loc tvs
- = do { lvl <- getTcLevel
- ; instSkolTyCoVars (mkTcSkolTyVar lvl loc False) tvs }
+ details = SkolemTv lvl overlappable
+ new_skol_tv name kind = mkTcTyVar name kind details
------------------
-freshenTyVarBndrs :: [TyVar] -> TcRnIf gbl lcl (TCvSubst, [TyVar])
+freshenTyVarBndrs :: [TyVar] -> TcM (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 uniq old_name kind = mkTyVar (setNameUnique old_name uniq) kind
+freshenTyVarBndrs = freshenTyCoVars mkTyVar
-freshenCoVarBndrsX :: TCvSubst -> [CoVar] -> TcRnIf gbl lcl (TCvSubst, [CoVar])
+freshenCoVarBndrsX :: TCvSubst -> [CoVar] -> TcM (TCvSubst, [CoVar])
-- ^ Give fresh uniques to a bunch of CoVars
-- Used in FamInst.newFamInst
-freshenCoVarBndrsX subst = instSkolTyCoVarsX mk_cv subst
- where
- mk_cv uniq old_name kind = mkCoVar (setNameUnique old_name uniq) kind
+freshenCoVarBndrsX subst = freshenTyCoVarsX mkCoVar subst
------------------
-type TcTyVarMaker = Unique -> Name -> Kind -> TyCoVar
-instSkolTyCoVars :: TcTyVarMaker -> [TyVar] -> TcRnIf gbl lcl (TCvSubst, [TyCoVar])
-instSkolTyCoVars mk_tcv = instSkolTyCoVarsX mk_tcv emptyTCvSubst
-
-instSkolTyCoVarsX :: TcTyVarMaker
- -> TCvSubst -> [TyCoVar] -> TcRnIf gbl lcl (TCvSubst, [TyCoVar])
-instSkolTyCoVarsX mk_tcv = mapAccumLM (instSkolTyCoVarX mk_tcv)
-
-instSkolTyCoVarX :: TcTyVarMaker
- -> TCvSubst -> TyCoVar -> TcRnIf gbl lcl (TCvSubst, TyCoVar)
-instSkolTyCoVarX mk_tcv subst tycovar
- = do { uniq <- newUnique -- using a new unique is critical. See
- -- Note [Skolems in zonkSyntaxExpr] in TcHsSyn
- ; let new_tcv = mk_tcv uniq old_name kind
- 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)
+freshenTyCoVars :: (Name -> Kind -> TyCoVar)
+ -> [TyVar] -> TcM (TCvSubst, [TyCoVar])
+freshenTyCoVars mk_tcv = freshenTyCoVarsX mk_tcv emptyTCvSubst
+
+freshenTyCoVarsX :: (Name -> Kind -> TyCoVar)
+ -> TCvSubst -> [TyCoVar]
+ -> TcM (TCvSubst, [TyCoVar])
+freshenTyCoVarsX mk_tcv = mapAccumLM (freshenTyCoVarX mk_tcv)
+
+freshenTyCoVarX :: (Name -> Kind -> TyCoVar)
+ -> TCvSubst -> TyCoVar -> TcM (TCvSubst, TyCoVar)
+-- This a complete freshening operation:
+-- the skolems have a fresh unique, and a location from the monad
+-- See Note [Skolemising type variables]
+freshenTyCoVarX mk_tcv subst tycovar
+ = do { loc <- getSrcSpanM
+ ; uniq <- newUnique
+ ; let old_name = tyVarName tycovar
+ new_name = mkInternalName uniq (getOccName old_name) loc
+ new_kind = substTyUnchecked subst (tyVarKind tycovar)
+ new_tcv = mk_tcv new_name new_kind
+ subst1 = extendTCvSubstWithClone subst tycovar new_tcv
+ ; return (subst1, new_tcv) }
+
+{- Note [Skolemising type variables]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+The tcInstSkolTyVars family of functions instantiate a list of TyVars
+to fresh skolem TcTyVars. Important notes:
+
+a) Level allocation. We generally skolemise /before/ calling
+ pushLevelAndCaptureConstraints. So we want their level to the level
+ of the soon-to-be-created implication, which has a level ONE HIGHER
+ than the current level. Hence the pushTcLevel. It feels like a
+ slight hack.
+
+b) The [TyVar] should be ordered (kind vars first)
+ See Note [Kind substitution when instantiating]
+
+c) It's a complete freshening operation: the skolems have a fresh
+ unique, and a location from the monad
+
+d) The resulting skolems are
+ non-overlappable for tcInstSkolTyVars,
+ but overlappable for tcInstSuperSkolTyVars
+ See TcDerivInfer Note [Overlap and deriving] for an example
+ of where this matters.
-newFskTyVar :: TcType -> TcM TcTyVar
-newFskTyVar fam_ty
- = do { uniq <- newUnique
- ; let name = mkSysTvName uniq (fsLit "fsk")
- ; return (mkTcTyVar name (typeKind fam_ty) (FlatSkol fam_ty)) }
-{-
Note [Kind substitution when instantiating]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
When we instantiate a bunch of kind and type variables, first we
************************************************************************
-}
-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 = mkSysTvName uniq str
+{-
+Note [TyVarTv]
+~~~~~~~~~~~~
+
+A TyVarTv can unify with type *variables* only, including other TyVarTvs and
+skolems. Sometimes, they can unify with type variables that the user would
+rather keep distinct; see #11203 for an example. So, any client of this
+function needs to either allow the TyVarTvs to unify with each other or check
+that they don't (say, with a call to findDubTyVarTvs).
+
+Before #15050 this (under the name SigTv) was used for ScopedTypeVariables in
+patterns, to make sure these type variables only refer to other type variables,
+but this restriction was dropped, and ScopedTypeVariables can now refer to full
+types (GHC Proposal 29).
+
+The remaining uses of newTyVarTyVars are
+* In kind signatures, see
+ TcTyClsDecls Note [Inferring kinds for type declarations]
+ and Note [Kind checking for GADTs]
+* In partial type signatures, see Note [Quantified variables in partial type signatures]
+-}
-newSigTyVar :: Name -> Kind -> TcM TcTyVar
-newSigTyVar name kind
- = do { details <- newMetaDetails SigTv
- ; return (mkTcTyVar name kind details) }
+-- see Note [TyVarTv]
+newTyVarTyVar :: Name -> Kind -> TcM TcTyVar
+newTyVarTyVar name kind
+ = do { details <- newMetaDetails TyVarTv
+ ; let tyvar = mkTcTyVar name kind details
+ ; traceTc "newTyVarTyVar" (ppr tyvar)
+ ; return tyvar }
+
+
+-- makes a new skolem tv
+newSkolemTyVar :: Name -> Kind -> TcM TcTyVar
+newSkolemTyVar name kind = do { lvl <- getTcLevel
+ ; return (mkTcTyVar name kind (SkolemTv lvl False)) }
+
+newFskTyVar :: TcType -> TcM TcTyVar
+newFskTyVar fam_ty
+ = do { uniq <- newUnique
+ ; ref <- newMutVar Flexi
+ ; tclvl <- getTcLevel
+ ; let details = MetaTv { mtv_info = FlatSkolTv
+ , mtv_ref = ref
+ , mtv_tclvl = tclvl }
+ name = mkMetaTyVarName uniq (fsLit "fsk")
+ ; return (mkTcTyVar name (tcTypeKind fam_ty) details) }
newFmvTyVar :: TcType -> TcM TcTyVar
-- Very like newMetaTyVar, except sets mtv_tclvl to one less
newFmvTyVar fam_ty
= do { uniq <- newUnique
; ref <- newMutVar Flexi
- ; cur_lvl <- getTcLevel
+ ; tclvl <- getTcLevel
; let details = MetaTv { mtv_info = FlatMetaTv
, mtv_ref = ref
- , mtv_tclvl = fmvTcLevel cur_lvl }
+ , mtv_tclvl = tclvl }
name = mkMetaTyVarName uniq (fsLit "s")
- ; return (mkTcTyVar name (typeKind fam_ty) details) }
+ ; return (mkTcTyVar name (tcTypeKind fam_ty) details) }
newMetaDetails :: MetaInfo -> TcM TcTyVarDetails
newMetaDetails info
details' = case tcTyVarDetails tv of
details@(MetaTv {}) -> details { mtv_ref = ref }
_ -> pprPanic "cloneMetaTyVar" (ppr tv)
- ; return (mkTcTyVar name' (tyVarKind tv) details') }
+ tyvar = mkTcTyVar name' (tyVarKind tv) details'
+ ; traceTc "cloneMetaTyVar" (ppr tyvar)
+ ; return tyvar }
-- Works for both type and kind variables
readMetaTyVar :: TyVar -> TcM MetaDetails
readMetaTyVar tyvar = ASSERT2( isMetaTyVar tyvar, ppr tyvar )
readMutVar (metaTyVarRef tyvar)
+isFilledMetaTyVar_maybe :: TcTyVar -> TcM (Maybe Type)
+isFilledMetaTyVar_maybe tv
+ | MetaTv { mtv_ref = ref } <- tcTyVarDetails tv
+ = do { cts <- readTcRef ref
+ ; case cts of
+ Indirect ty -> return (Just ty)
+ Flexi -> return Nothing }
+ | otherwise
+ = return Nothing
+
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
+isFilledMetaTyVar tv = isJust <$> isFilledMetaTyVar_maybe tv
isUnfilledMetaTyVar :: TyVar -> TcM Bool
-- True of a un-filled-in (Flexi) meta type variable
+-- NB: Not the opposite of isFilledMetaTyVar
isUnfilledMetaTyVar tv
| MetaTv { mtv_ref = ref } <- tcTyVarDetails tv
= do { details <- readMutVar ref
-- Everything from here on only happens if DEBUG is on
| not (isTcTyVar tyvar)
- = WARN( True, text "Writing to non-tc tyvar" <+> ppr tyvar )
+ = ASSERT2( False, 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 )
+ = ASSERT2( False, text "Writing to non-meta tyvar" <+> ppr tyvar )
return ()
--------------------
= 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
+ ; zonked_ty <- zonkTcType ty
+ ; let zonked_ty_kind = tcTypeKind zonked_ty -- Need to zonk even before typeKind;
+ -- otherwise, we can panic in piResultTy
+ kind_check_ok = tcIsConstraintKind zonked_tv_kind
|| tcEqKind zonked_ty_kind zonked_tv_kind
+ -- Hack alert! tcIsConstraintKind: 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) )
+ <+> ppr ty <+> text "::" <+> (ppr zonked_ty_kind) )
; traceTc "writeMetaTyVar" (ppr tyvar <+> text ":=" <+> ppr ty)
; writeMutVar ref (Indirect ty) }
where
tv_kind = tyVarKind tyvar
- ty_kind = typeKind ty
tv_lvl = tcTyVarLevel tyvar
ty_lvl = tcTypeLevel ty
- level_check_ok = isFmvTyVar tyvar
- || not (ty_lvl `strictlyDeeperThan` tv_lvl)
+ level_check_ok = 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
% 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
{-
************************************************************************
that can't ever appear in user code, so we're safe!
-}
+newTauTyVar :: Name -> Kind -> TcM TcTyVar
+newTauTyVar name kind
+ = do { details <- newMetaDetails TauTv
+ ; let tyvar = mkTcTyVar name kind details
+ ; traceTc "newTauTyVar" (ppr tyvar)
+ ; return tyvar }
+
+
+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
s = case meta_info of
TauTv -> fsLit "t"
FlatMetaTv -> fsLit "fmv"
- SigTv -> fsLit "a"
+ FlatSkolTv -> fsLit "fsk"
+ TyVarTv -> fsLit "a"
; details <- newMetaDetails meta_info
- ; return (mkTcTyVar name kind details) }
+ ; let tyvar = mkTcTyVar name kind details
+ ; traceTc "newAnonMetaTyVar" (ppr tyvar)
+ ; return tyvar }
+
+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]
+ tyvar = mkTcTyVar name kind details
+ ; traceTc "cloneAnonMetaTyVar" (ppr tyvar)
+ ; return tyvar }
+
+{- 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
= 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
+newMetaTyVars = newMetaTyVarsX 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.
+newMetaTyVarsX :: TCvSubst -> [TyVar] -> TcM (TCvSubst, [TcTyVar])
+-- Just like newMetaTyVars, but start with an existing substitution.
+newMetaTyVarsX subst = mapAccumLM newMetaTyVarX subst
+
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
-newMetaSigTyVarX :: TCvSubst -> TyVar -> TcM (TCvSubst, TcTyVar)
--- Just like newMetaTyVarX, but make a SigTv
-newMetaSigTyVarX subst tyvar = new_meta_tv_x SigTv subst tyvar
+newMetaTyVarTyVars :: [TyVar] -> TcM (TCvSubst, [TcTyVar])
+newMetaTyVarTyVars = mapAccumLM newMetaTyVarTyVarX emptyTCvSubst
+
+newMetaTyVarTyVarX :: TCvSubst -> TyVar -> TcM (TCvSubst, TcTyVar)
+-- Just like newMetaTyVarX, but make a TyVarTv
+newMetaTyVarTyVarX subst tyvar = new_meta_tv_x TyVarTv subst tyvar
newWildCardX :: TCvSubst -> TyVar -> TcM (TCvSubst, TcTyVar)
newWildCardX subst tv
new_meta_tv_x :: MetaInfo -> TCvSubst -> TyVar -> TcM (TCvSubst, TcTyVar)
new_meta_tv_x info subst tv
- = do { uniq <- newUnique
- ; details <- newMetaDetails info
- ; let name = mkSystemName uniq (getOccName tv)
- -- See Note [Name of an instantiated type variable]
- kind = substTyUnchecked subst (tyVarKind tv)
- -- Unchecked because we call newMetaTyVarX from
- -- tcInstBinderX, 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
- new_tv = mkTcTyVar name kind details
- subst1 = extendTvSubstWithClone subst tv new_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
+ -- tcInstTyBinder, which is called from tcInferApps
+ -- 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
, mtv_tclvl = tc_lvl }
; return (mkTyVarTy (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.
+{- *********************************************************************
+* *
+ Finding variables to quantify over
+* *
+********************************************************************* -}
-************************************************************************
+{- Note [Dependent type variables]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+In Haskell type inference we quantify over type variables; but we only
+quantify over /kind/ variables when -XPolyKinds is on. Without -XPolyKinds
+we default the kind variables to *.
+
+So, to support this defaulting, and only for that reason, when
+collecting the free vars of a type, prior to quantifying, we must keep
+the type and kind variables separate.
+
+But what does that mean in a system where kind variables /are/ type
+variables? It's a fairly arbitrary distinction based on how the
+variables appear:
+
+ - "Kind variables" appear in the kind of some other free variable
+
+ These are the ones we default to * if -XPolyKinds is off
+
+ - "Type variables" are all free vars that are not kind variables
+
+E.g. In the type T k (a::k)
+ 'k' is a kind variable, because it occurs in the kind of 'a',
+ even though it also appears at "top level" of the type
+ 'a' is a type variable, because it doesn't
+
+We gather these variables using a CandidatesQTvs record:
+ DV { dv_kvs: Variables free in the kind of a free type variable
+ or of a forall-bound type variable
+ , dv_tvs: Variables sytactically free in the type }
+
+So: dv_kvs are the kind variables of the type
+ (dv_tvs - dv_kvs) are the type variable of the type
+
+Note that
+
+* A variable can occur in both.
+ T k (x::k) The first occurrence of k makes it
+ show up in dv_tvs, the second in dv_kvs
+
+* We include any coercion variables in the "dependent",
+ "kind-variable" set because we never quantify over them.
+
+* The "kind variables" might depend on each other; e.g
+ (k1 :: k2), (k2 :: *)
+ The "type variables" do not depend on each other; if
+ one did, it'd be classified as a kind variable!
+
+Note [CandidatesQTvs determinism and order]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+* Determinism: when we quantify over type variables we decide the
+ order in which they appear in the final type. Because the order of
+ type variables in the type can end up in the interface file and
+ affects some optimizations like worker-wrapper, we want this order to
+ be deterministic.
+
+ To achieve that we use deterministic sets of variables that can be
+ converted to lists in a deterministic order. For more information
+ about deterministic sets see Note [Deterministic UniqFM] in UniqDFM.
+
+* Order: as well as being deterministic, we use an
+ accumulating-parameter style for candidateQTyVarsOfType so that we
+ add variables one at a time, left to right. That means we tend to
+ produce the variables in left-to-right order. This is just to make
+ it bit more predicatable for the programmer.
+
+Note [Naughty quantification candidates]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Consider (#14880, dependent/should_compile/T14880-2), suppose
+we are trying to generalise this type:
+
+ forall arg. ... (alpha[tau]:arg) ...
+
+We have a metavariable alpha whose kind mentions a skolem variable
+bound inside the very type we are generalising.
+This can arise while type-checking a user-written type signature
+(see the test case for the full code).
+
+We cannot generalise over alpha! That would produce a type like
+ forall {a :: arg}. forall arg. ...blah...
+The fact that alpha's kind mentions arg renders it completely
+ineligible for generalisation.
+
+However, we are not going to learn any new constraints on alpha,
+because its kind isn't even in scope in the outer context (but see Wrinkle).
+So alpha is entirely unconstrained.
+
+What then should we do with alpha? During generalization, every
+metavariable is either (A) promoted, (B) generalized, or (C) zapped
+(according again to Note [Recipe for checking a signature] in
+TcHsType).
+
+ * We can't generalise it.
+ * We can't promote it, because its kind prevents that
+ * We can't simply leave it be, because this type is about to
+ go into the typing environment (as the type of some let-bound
+ variable, say), and then chaos erupts when we try to instantiate.
+
+So, we zap it, eagerly, to Any. We don't have to do this eager zapping
+in terms (say, in `length []`) because terms are never re-examined before
+the final zonk (which zaps any lingering metavariables to Any).
+
+We do this eager zapping in candidateQTyVars, which always precedes
+generalisation, because at that moment we have a clear picture of
+what skolems are in scope.
+
+Wrinkle:
+
+We must make absolutely sure that alpha indeed is not
+from an outer context. (Otherwise, we might indeed learn more information
+about it.) This can be done easily: we just check alpha's TcLevel.
+That level must be strictly greater than the ambient TcLevel in order
+to treat it as naughty. We say "strictly greater than" because the call to
+candidateQTyVars is made outside the bumped TcLevel, as stated in the
+comment to candidateQTyVarsOfType. The level check is done in go_tv
+in collect_cant_qtvs. Skipping this check caused #16517.
+
+-}
+
+data CandidatesQTvs
+ -- See Note [Dependent type variables]
+ -- See Note [CandidatesQTvs determinism and order]
+ --
+ -- Invariants:
+ -- * All variables stored here are MetaTvs. No exceptions.
+ -- * All variables are fully zonked, including their kinds
+ --
+ = DV { dv_kvs :: DTyVarSet -- "kind" metavariables (dependent)
+ , dv_tvs :: DTyVarSet -- "type" metavariables (non-dependent)
+ -- A variable may appear in both sets
+ -- E.g. T k (x::k) The first occurrence of k makes it
+ -- show up in dv_tvs, the second in dv_kvs
+ -- See Note [Dependent type variables]
+
+ , dv_cvs :: CoVarSet
+ -- These are covars. We will *not* quantify over these, but
+ -- we must make sure also not to quantify over any cv's kinds,
+ -- so we include them here as further direction for quantifyTyVars
+ }
+
+instance Semi.Semigroup CandidatesQTvs where
+ (DV { dv_kvs = kv1, dv_tvs = tv1, dv_cvs = cv1 })
+ <> (DV { dv_kvs = kv2, dv_tvs = tv2, dv_cvs = cv2 })
+ = DV { dv_kvs = kv1 `unionDVarSet` kv2
+ , dv_tvs = tv1 `unionDVarSet` tv2
+ , dv_cvs = cv1 `unionVarSet` cv2 }
+
+instance Monoid CandidatesQTvs where
+ mempty = DV { dv_kvs = emptyDVarSet, dv_tvs = emptyDVarSet, dv_cvs = emptyVarSet }
+ mappend = (Semi.<>)
+
+instance Outputable CandidatesQTvs where
+ ppr (DV {dv_kvs = kvs, dv_tvs = tvs, dv_cvs = cvs })
+ = text "DV" <+> braces (pprWithCommas id [ text "dv_kvs =" <+> ppr kvs
+ , text "dv_tvs =" <+> ppr tvs
+ , text "dv_cvs =" <+> ppr cvs ])
+
+
+candidateKindVars :: CandidatesQTvs -> TyVarSet
+candidateKindVars dvs = dVarSetToVarSet (dv_kvs dvs)
+
+-- | Gathers free variables to use as quantification candidates (in
+-- 'quantifyTyVars'). This might output the same var
+-- in both sets, if it's used in both a type and a kind.
+-- The variables to quantify must have a TcLevel strictly greater than
+-- the ambient level. (See Wrinkle in Note [Naughty quantification candidates])
+-- See Note [CandidatesQTvs determinism and order]
+-- See Note [Dependent type variables]
+candidateQTyVarsOfType :: TcType -- not necessarily zonked
+ -> TcM CandidatesQTvs
+candidateQTyVarsOfType ty = collect_cand_qtvs False emptyVarSet mempty ty
+
+-- | Like 'candidateQTyVarsOfType', but over a list of types
+-- The variables to quantify must have a TcLevel strictly greater than
+-- the ambient level. (See Wrinkle in Note [Naughty quantification candidates])
+candidateQTyVarsOfTypes :: [Type] -> TcM CandidatesQTvs
+candidateQTyVarsOfTypes tys = foldlM (collect_cand_qtvs False emptyVarSet) mempty tys
+
+-- | Like 'candidateQTyVarsOfType', but consider every free variable
+-- to be dependent. This is appropriate when generalizing a *kind*,
+-- instead of a type. (That way, -XNoPolyKinds will default the variables
+-- to Type.)
+candidateQTyVarsOfKind :: TcKind -- Not necessarily zonked
+ -> TcM CandidatesQTvs
+candidateQTyVarsOfKind ty = collect_cand_qtvs True emptyVarSet mempty ty
+
+candidateQTyVarsOfKinds :: [TcKind] -- Not necessarily zonked
+ -> TcM CandidatesQTvs
+candidateQTyVarsOfKinds tys = foldM (collect_cand_qtvs True emptyVarSet) mempty tys
+
+delCandidates :: CandidatesQTvs -> [Var] -> CandidatesQTvs
+delCandidates (DV { dv_kvs = kvs, dv_tvs = tvs, dv_cvs = cvs }) vars
+ = DV { dv_kvs = kvs `delDVarSetList` vars
+ , dv_tvs = tvs `delDVarSetList` vars
+ , dv_cvs = cvs `delVarSetList` vars }
+
+collect_cand_qtvs
+ :: Bool -- True <=> consider every fv in Type to be dependent
+ -> VarSet -- Bound variables (locals only)
+ -> CandidatesQTvs -- Accumulating parameter
+ -> Type -- Not necessarily zonked
+ -> TcM CandidatesQTvs
+
+-- Key points:
+-- * Looks through meta-tyvars as it goes;
+-- no need to zonk in advance
+--
+-- * Needs to be monadic anyway, because it does the zap-naughty
+-- stuff; see Note [Naughty quantification candidates]
+--
+-- * Returns fully-zonked CandidateQTvs, including their kinds
+-- so that subsequent dependency analysis (to build a well
+-- scoped telescope) works correctly
+
+collect_cand_qtvs is_dep bound dvs ty
+ = go dvs ty
+ where
+ is_bound tv = tv `elemVarSet` bound
+
+ -----------------
+ go :: CandidatesQTvs -> TcType -> TcM CandidatesQTvs
+ -- Uses accumulating-parameter style
+ go dv (AppTy t1 t2) = foldlM go dv [t1, t2]
+ go dv (TyConApp _ tys) = foldlM go dv tys
+ go dv (FunTy arg res) = foldlM go dv [arg, res]
+ go dv (LitTy {}) = return dv
+ go dv (CastTy ty co) = do dv1 <- go dv ty
+ collect_cand_qtvs_co bound dv1 co
+ go dv (CoercionTy co) = collect_cand_qtvs_co bound dv co
+
+ go dv (TyVarTy tv)
+ | is_bound tv = return dv
+ | otherwise = do { m_contents <- isFilledMetaTyVar_maybe tv
+ ; case m_contents of
+ Just ind_ty -> go dv ind_ty
+ Nothing -> go_tv dv tv }
+
+ go dv (ForAllTy (Bndr tv _) ty)
+ = do { dv1 <- collect_cand_qtvs True bound dv (tyVarKind tv)
+ ; collect_cand_qtvs is_dep (bound `extendVarSet` tv) dv1 ty }
+
+ -----------------
+ go_tv dv@(DV { dv_kvs = kvs, dv_tvs = tvs }) tv
+ | tv `elemDVarSet` kvs
+ = return dv -- We have met this tyvar aleady
+
+ | not is_dep
+ , tv `elemDVarSet` tvs
+ = return dv -- We have met this tyvar aleady
+
+ | otherwise
+ = do { tv_kind <- zonkTcType (tyVarKind tv)
+ -- This zonk is annoying, but it is necessary, both to
+ -- ensure that the collected candidates have zonked kinds
+ -- (Trac #15795) and to make the naughty check
+ -- (which comes next) works correctly
+
+ ; cur_lvl <- getTcLevel
+ ; if tcTyVarLevel tv `strictlyDeeperThan` cur_lvl &&
+ -- this tyvar is from an outer context: see Wrinkle
+ -- in Note [Naughty quantification candidates]
+
+ intersectsVarSet bound (tyCoVarsOfType tv_kind)
+
+ then -- See Note [Naughty quantification candidates]
+ do { traceTc "Zapping naughty quantifier" (pprTyVar tv)
+ ; writeMetaTyVar tv (anyTypeOfKind tv_kind)
+ ; collect_cand_qtvs True bound dv tv_kind }
+
+ else do { let tv' = tv `setTyVarKind` tv_kind
+ dv' | is_dep = dv { dv_kvs = kvs `extendDVarSet` tv' }
+ | otherwise = dv { dv_tvs = tvs `extendDVarSet` tv' }
+ -- See Note [Order of accumulation]
+ ; collect_cand_qtvs True emptyVarSet dv' tv_kind } }
+
+collect_cand_qtvs_co :: VarSet -- bound variables
+ -> CandidatesQTvs -> Coercion
+ -> TcM CandidatesQTvs
+collect_cand_qtvs_co bound = go_co
+ where
+ go_co dv (Refl ty) = collect_cand_qtvs True bound dv ty
+ go_co dv (GRefl _ ty mco) = do dv1 <- collect_cand_qtvs True bound dv ty
+ go_mco dv1 mco
+ go_co dv (TyConAppCo _ _ cos) = foldlM go_co dv cos
+ go_co dv (AppCo co1 co2) = foldlM go_co dv [co1, co2]
+ go_co dv (FunCo _ co1 co2) = foldlM go_co dv [co1, co2]
+ go_co dv (AxiomInstCo _ _ cos) = foldlM go_co dv cos
+ go_co dv (AxiomRuleCo _ cos) = foldlM go_co dv cos
+ go_co dv (UnivCo prov _ t1 t2) = do dv1 <- go_prov dv prov
+ dv2 <- collect_cand_qtvs True bound dv1 t1
+ collect_cand_qtvs True bound dv2 t2
+ go_co dv (SymCo co) = go_co dv co
+ go_co dv (TransCo co1 co2) = foldlM go_co dv [co1, co2]
+ go_co dv (NthCo _ _ co) = go_co dv co
+ go_co dv (LRCo _ co) = go_co dv co
+ go_co dv (InstCo co1 co2) = foldlM go_co dv [co1, co2]
+ go_co dv (KindCo co) = go_co dv co
+ go_co dv (SubCo co) = go_co dv co
+
+ go_co dv (HoleCo hole) = do m_co <- unpackCoercionHole_maybe hole
+ case m_co of
+ Just co -> go_co dv co
+ Nothing -> go_cv dv (coHoleCoVar hole)
+
+ go_co dv (CoVarCo cv) = go_cv dv cv
+
+ go_co dv (ForAllCo tcv kind_co co)
+ = do { dv1 <- go_co dv kind_co
+ ; collect_cand_qtvs_co (bound `extendVarSet` tcv) dv1 co }
+
+ go_mco dv MRefl = return dv
+ go_mco dv (MCo co) = go_co dv co
+
+ go_prov dv UnsafeCoerceProv = return dv
+ go_prov dv (PhantomProv co) = go_co dv co
+ go_prov dv (ProofIrrelProv co) = go_co dv co
+ go_prov dv (PluginProv _) = return dv
+
+ go_cv :: CandidatesQTvs -> CoVar -> TcM CandidatesQTvs
+ go_cv dv@(DV { dv_cvs = cvs }) cv
+ | is_bound cv = return dv
+ | cv `elemVarSet` cvs = return dv
+ | otherwise = collect_cand_qtvs True emptyVarSet
+ (dv { dv_cvs = cvs `extendVarSet` cv })
+ (idType cv)
+
+ is_bound tv = tv `elemVarSet` bound
+
+{- Note [Order of accumulation]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+You might be tempted (like I was) to use unitDVarSet and mappend
+rather than extendDVarSet. However, the union algorithm for
+deterministic sets depends on (roughly) the size of the sets. The
+elements from the smaller set end up to the right of the elements from
+the larger one. When sets are equal, the left-hand argument to
+`mappend` goes to the right of the right-hand argument.
+
+In our case, if we use unitDVarSet and mappend, we learn that the free
+variables of (a -> b -> c -> d) are [b, a, c, d], and we then quantify
+over them in that order. (The a comes after the b because we union the
+singleton sets as ({a} `mappend` {b}), producing {b, a}. Thereafter,
+the size criterion works to our advantage.) This is just annoying to
+users, so I use `extendDVarSet`, which unambiguously puts the new
+element to the right.
+
+Note that the unitDVarSet/mappend implementation would not be wrong
+against any specification -- just suboptimal and confounding to users.
+-}
+
+{- *********************************************************************
* *
Quantification
* *
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
+ 3. Calls skolemiseQuantifiedTyVar 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).
+has free vars {f,a}, but we must add 'k' as well! Hence step (2).
* 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 coercion variable (or any tv mentioned in the kind of a covar)
- a runtime-rep variable
Note [quantifyTyVars determinism]
the results of optimizations, for example worker-wrapper. This means that to
get deterministic builds quantifyTyVars needs to be deterministic.
-To achieve this TcDepVars is backed by deterministic sets which allows them
+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, quantifyZonkedTyVars
- :: TcTyCoVarSet -- global tvs
- -> TcDepVars -- See Note [Dependent type variables] in TcType
+quantifyTyVars
+ :: TcTyCoVarSet -- Global tvs; already zonked
+ -> CandidatesQTvs -- See Note [Dependent type variables]
+ -- 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, dv_cvs = covars })
+ = do { outer_tclvl <- getTcLevel
+ ; traceTc "quantifyTyVars 1" (vcat [ppr outer_tclvl, ppr dvs, ppr gbl_tvs])
+ ; let co_tvs = closeOverKinds covars
+ mono_tvs = gbl_tvs `unionVarSet` co_tvs
+ -- NB: All variables in the kind of a covar must not be
+ -- quantified over, as we don't quantify over the covar.
--- The zonked variant assumes everything is already zonked.
-
-quantifyTyVars gbl_tvs (DV { dv_kvs = dep_tkvs, dv_tvs = nondep_tkvs })
- = do { dep_tkvs <- zonkTyCoVarsAndFVDSet dep_tkvs
- ; nondep_tkvs <- zonkTyCoVarsAndFVDSet nondep_tkvs
- ; gbl_tvs <- zonkTyCoVarsAndFV gbl_tvs
- ; quantifyZonkedTyVars gbl_tvs (DV { dv_kvs = dep_tkvs, dv_tvs = nondep_tkvs }) }
-
-quantifyZonkedTyVars gbl_tvs dvs@(DV{ dv_kvs = dep_tkvs, dv_tvs = nondep_tkvs })
- = do { traceTc "quantifyZonkedTyVars" (vcat [ppr dvs, ppr gbl_tvs])
- ; let all_cvs = filterVarSet isCoVar $ dVarSetToVarSet dep_tkvs
dep_kvs = dVarSetElemsWellScoped $
- dep_tkvs `dVarSetMinusVarSet` gbl_tvs
- `dVarSetMinusVarSet` closeOverKinds all_cvs
- -- dVarSetElemsWellScoped: put the kind variables into
- -- well-scoped order.
- -- E.g. [k, (a::k)] not the other way roud
- -- closeOverKinds all_cvs: do not quantify over coercion
- -- variables, or any any tvs that a covar depends on
+ dep_tkvs `dVarSetMinusVarSet` mono_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
+ `dVarSetMinusVarSet` mono_tvs
+ -- See Note [Dependent type variables]
-- 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
+ -- This block uses level numbers to decide what to quantify
+ -- and emits a warning if the two methods do not give the same answer
+ ; let dep_kvs2 = dVarSetElemsWellScoped $
+ filterDVarSet (quantifiableTv outer_tclvl) dep_tkvs
+ nondep_tvs2 = filter (quantifiableTv outer_tclvl) $
+ dVarSetElems (nondep_tkvs `minusDVarSet` dep_tkvs)
+
+ all_ok = dep_kvs == dep_kvs2 && nondep_tvs == nondep_tvs2
+ bad_msg = hang (text "Quantification by level numbers would fail")
+ 2 (vcat [ text "Outer level =" <+> ppr outer_tclvl
+ , text "dep_tkvs =" <+> ppr dep_tkvs
+ , text "co_vars =" <+> vcat [ ppr cv <+> dcolon <+> ppr (varType cv)
+ | cv <- nonDetEltsUniqSet covars ]
+ , text "co_tvs =" <+> ppr co_tvs
+ , text "dep_kvs =" <+> ppr dep_kvs
+ , text "dep_kvs2 =" <+> ppr dep_kvs2
+ , text "nondep_tvs =" <+> ppr nondep_tvs
+ , text "nondep_tvs2 =" <+> ppr nondep_tvs2 ])
+ ; WARN( not all_ok, bad_msg ) return ()
+
-- 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
; 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:" <+> ppr nondep_tvs
- , text "dep:" <+> ppr dep_kvs
- , text "dep_kvs'" <+> ppr dep_kvs'
- , text "nondep_tvs'" <+> ppr nondep_tvs' ])
+ ; traceTc "quantifyTyVars 2"
+ (vcat [ text "globals:" <+> ppr gbl_tvs
+ , text "mono_tvs:" <+> ppr mono_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 (dep_kvs' ++ nondep_tvs') }
+ ; 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
- | isTcTyVar tkv = zonkQuantifiedTyVar default_kind tkv
- | otherwise = return $ Just tkv
- -- For associated types, we have the class variables
- -- in scope, and they are TyVars not TcTyVars
-
-zonkQuantifiedTyVar :: Bool -- True <=> this is a kind var and -XNoPolyKinds
- -- False <=> not a kind var or -XPolyKinds
- -> TcTyVar
- -> TcM (Maybe TcTyVar)
+ | not (isTyVar tkv)
+ = return Nothing -- this can happen for a covar that's associated with
+ -- a coercion hole. Test case: typecheck/should_compile/T2494
+
+ | not (isTcTyVar tkv) -- I don't think this can ever happen.
+ -- Hence the assert
+ = ASSERT2( False, text "quantifying over a TyVar" <+> ppr tkv)
+ return (Just tkv)
+
+ | otherwise
+ = do { deflt_done <- defaultTyVar default_kind tkv
+ ; case deflt_done of
+ True -> return Nothing
+ False -> do { tv <- skolemiseQuantifiedTyVar tkv
+ ; return (Just tv) } }
+
+quantifiableTv :: TcLevel -- Level of the context, outside the quantification
+ -> TcTyVar
+ -> Bool
+quantifiableTv outer_tclvl tcv
+ | isTcTyVar tcv -- Might be a CoVar; change this when gather covars separtely
+ = tcTyVarLevel tcv > outer_tclvl
+ | otherwise
+ = False
+
+skolemiseQuantifiedTyVar :: TcTyVar -> TcM TcTyVar
-- The quantified type variables often include meta type variables
--- we want to freeze them into ordinary type variables, and
--- default their kind (e.g. from TYPE v to TYPE Lifted)
+-- 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.
--
-- This function is called on both kind and type variables,
-- but kind variables *only* if PolyKinds is on.
---
--- This 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
-zonkQuantifiedTyVar default_kind tv
+skolemiseQuantifiedTyVar tv
= case tcTyVarDetails tv of
SkolemTv {} -> do { kind <- zonkTcType (tyVarKind tv)
- ; return $ Just (setTyVarKind tv kind) }
+ ; return (setTyVarKind tv kind) }
-- It might be a skolem type variable,
-- for example from a user type signature
- MetaTv { mtv_ref = ref }
- -> do { when debugIsOn (check_empty ref)
- ; zonk_meta_tv tv }
+ MetaTv {} -> skolemiseUnboundMetaTyVar tv
- _other -> pprPanic "zonkQuantifiedTyVar" (ppr tv) -- FlatSkol, RuntimeUnk
+ _other -> pprPanic "skolemiseQuantifiedTyVar" (ppr tv) -- RuntimeUnk
- where
- zonk_meta_tv :: TcTyVar -> TcM (Maybe TcTyVar)
- zonk_meta_tv tv
- | isRuntimeRepVar tv -- Never quantify over a RuntimeRep var
- = do { writeMetaTyVar tv ptrRepLiftedTy
- ; return Nothing }
+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
- | default_kind -- -XNoPolyKinds and this is a kind var
- = do { _ <- default_kind_var tv
- ; return Nothing }
+defaultTyVar default_kind tv
+ | not (isMetaTyVar tv)
+ = return False
- | otherwise
- = do { tv' <- skolemiseUnboundMetaTyVar tv
- ; return (Just tv') }
+ | isTyVarTyVar tv
+ -- Do not default TyVarTvs. Doing so would violate the invariants
+ -- on TyVarTvs; see Note [Signature skolems] in TcType.
+ -- Trac #13343 is an example; #14555 is another
+ -- See Note [Inferring kinds for type declarations] in TcTyClsDecls
+ = return False
+
+
+ | isRuntimeRepVar tv -- Do not quantify over a RuntimeRep var
+ -- unless it is a TyVarTv, handled earlier
+ = do { traceTc "Defaulting a RuntimeRep var to LiftedRep" (ppr tv)
+ ; writeMetaTyVar tv liftedRepTy
+ ; return True }
- default_kind_var :: TyVar -> TcM Type
+ | 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 { writeMetaTyVar kv liftedTypeKind
- ; return liftedTypeKind }
+ | isLiftedTypeKind (tyVarKind kv)
+ = do { traceTc "Defaulting a kind var to *" (ppr kv)
+ ; writeMetaTyVar kv liftedTypeKind }
| otherwise
- = do { 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" ])
- ; return (mkTyVarTy kv) }
+ = 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
- check_empty ref -- [Sept 04] Check for non-empty.
- = when debugIsOn $ -- See note [Silly Type Synonym]
- do { cts <- readMutVar ref
- ; case cts of
- Flexi -> return ()
- Indirect ty -> WARN( True, ppr tv $$ ppr ty )
- return () }
-
-skolemiseRuntimeUnk :: TcTyVar -> TcM TyVar
-skolemiseRuntimeUnk tv
- = skolemise_tv tv RuntimeUnk
-
skolemiseUnboundMetaTyVar :: TcTyVar -> TcM TyVar
-skolemiseUnboundMetaTyVar tv
- = skolemise_tv tv (SkolemTv (metaTyVarTcLevel tv) False)
-
-skolemise_tv :: TcTyVar -> TcTyVarDetails -> TcM TyVar
-- We have a Meta tyvar with a ref-cell inside it
--- Skolemise it, so that
--- we are totally out of Meta-tyvar-land
--- We create a skolem TyVar, not a regular TyVar
+-- Skolemise it, so that we are totally out of Meta-tyvar-land
+-- We create a skolem TcTyVar, not a regular TyVar
-- See Note [Zonking to Skolem]
-skolemise_tv tv details
+skolemiseUnboundMetaTyVar tv
= ASSERT2( isMetaTyVar tv, ppr tv )
- do { span <- getSrcSpanM -- Get the location from "here"
+ do { when debugIsOn (check_empty tv)
+ ; span <- getSrcSpanM -- Get the location from "here"
-- ie where we are generalising
; kind <- zonkTcType (tyVarKind tv)
; let uniq = getUnique tv
-- NB: Use same Unique as original tyvar. This is
- -- important for TcHsType.splitTelescopeTvs to work properly
+ -- convenient in reading dumps, but is otherwise inessential.
tv_name = getOccName tv
final_name = mkInternalName uniq tv_name span
; writeMetaTyVar tv (mkTyVarTy final_tv)
; return final_tv }
+ where
+ details = SkolemTv (metaTyVarTcLevel tv) False
+ check_empty tv -- [Sept 04] Check for non-empty.
+ = when debugIsOn $ -- See note [Silly Type Synonym]
+ do { cts <- readMetaTyVar tv
+ ; case cts of
+ Flexi -> return ()
+ Indirect ty -> WARN( True, ppr tv $$ ppr ty )
+ return () }
+
{- Note [Defaulting with -XNoPolyKinds]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider
variables (known as TcRefs).
Zonking is the process of ripping out these mutable variables and replacing them
-with a real TcType. This involves traversing the entire type expression, but the
+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:
-- 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.
+-- NB: This is closed over kinds, so it can return unification variables mentioned
+-- in the kinds of in-scope tyvars.
tcGetGlobalTyCoVars :: TcM TcTyVarSet
tcGetGlobalTyCoVars
= do { (TcLclEnv {tcl_tyvars = gtv_var}) <- getLclEnv
; 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*
-- 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 [Zonking within the knot] in TcHsType
zonkTcTypeAndFV ty
- = tyCoVarsOfTypeDSet <$> zonkTcTypeInKnot ty
-
--- | Zonk a type and call 'splitDepVarsOfType' on it.
--- Works within the knot.
-zonkTcTypeAndSplitDepVars :: TcType -> TcM TcDepVars
-zonkTcTypeAndSplitDepVars ty
- = splitDepVarsOfType <$> zonkTcTypeInKnot ty
-
-zonkTcTypesAndSplitDepVars :: [TcType] -> TcM TcDepVars
-zonkTcTypesAndSplitDepVars tys
- = splitDepVarsOfTypes <$> mapM zonkTcTypeInKnot tys
+ = tyCoVarsOfTypeDSet <$> zonkTcType ty
zonkTyCoVar :: TyCoVar -> TcM TcType
-- Works on TyVars and TcTyVars
| otherwise = ASSERT2( isCoVar tv, ppr tv )
mkCoercionTy . mkCoVarCo <$> zonkTyCoVarKind tv
-- Hackily, when typechecking type and class decls
- -- we have TyVars in scopeadded (only) in
- -- TcHsType.tcTyClTyVars, but it seems
+ -- we have TyVars in scope added (only) in
+ -- TcHsType.bindTyClTyVars, but it seems
-- painful to make them into TcTyVars there
zonkTyCoVarsAndFV :: TyCoVarSet -> TcM TyCoVarSet
-zonkTyCoVarsAndFV tycovars =
- tyCoVarsOfTypes <$> mapM zonkTyCoVar (nonDetEltsUFM tycovars)
- -- It's OK to use nonDetEltsUFM here because we immediately forget about
+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
-
--- Takes a deterministic set of TyCoVars, zonks them and returns a
--- deterministic set of their free variables.
--- See Note [quantifyTyVars determinism].
-zonkTyCoVarsAndFVDSet :: DTyCoVarSet -> TcM DTyCoVarSet
-zonkTyCoVarsAndFVDSet tycovars =
- tyCoVarsOfTypesDSet <$> mapM zonkTyCoVar (dVarSetElems tycovars)
+zonkTyCoVarsAndFVList tycovars
+ = tyCoVarsOfTypesList <$> mapM zonkTyCoVar tycovars
zonkTcTyVars :: [TcTyVar] -> TcM [TcType]
zonkTcTyVars tyvars = mapM zonkTcTyVar tyvars
, ic_given = given
, ic_wanted = wanted
, ic_info = info })
- = do { skols' <- mapM zonkTcTyCoVarBndr skols -- Need to zonk their kinds!
- -- as Trac #7230 showed
+ = do { skols' <- mapM zonkTyCoVarKind skols -- Need to zonk their kinds!
+ -- as Trac #7230 showed
; given' <- mapM zonkEvVar given
; info' <- zonkSkolemInfo info
; wanted' <- zonkWCRec wanted
zonkWC wc = zonkWCRec wc
zonkWCRec :: WantedConstraints -> TcM WantedConstraints
-zonkWCRec (WC { wc_simple = simple, wc_impl = implic, wc_insol = insol })
+zonkWCRec (WC { wc_simple = simple, wc_impl = implic })
= do { simple' <- zonkSimples simple
; implic' <- mapBagM zonkImplication implic
- ; insol' <- zonkSimples insol
- ; return (WC { wc_simple = simple', wc_impl = implic', wc_insol = insol' }) }
+ ; return (WC { wc_simple = simple', wc_impl = implic' }) }
zonkSimples :: Cts -> TcM Cts
zonkSimples cts = do { cts' <- mapBagM zonkCt' 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
- = do { fl' <- zonkCtEvidence (cc_ev ct)
+ = ASSERT( not (isCFunEqCan ct) )
+ -- We do not expect to see any CFunEqCans, because zonkCt is only called on
+ -- unflattened constraints.
+ do { fl' <- zonkCtEvidence (ctEvidence ct)
; return (mkNonCanonical fl') }
zonkCtEvidence :: CtEvidence -> TcM CtEvidence
; return (ctev { ctev_pred = pred' }) }
zonkSkolemInfo :: SkolemInfo -> TcM SkolemInfo
-zonkSkolemInfo (SigSkol cx ty) = do { ty' <- zonkTcType ty
- ; return (SigSkol cx ty') }
+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 { ty' <- zonkTcType (idType id)
; return (Id.setIdType id ty') }
--- | A suitable TyCoMapper for zonking a type inside the knot, and
+zonkCoVar :: CoVar -> TcM CoVar
+zonkCoVar = zonkId
+
+-- | A suitable TyCoMapper for zonking a type during type-checking,
-- before all metavars are filled in.
zonkTcTypeMapper :: TyCoMapper () TcM
zonkTcTypeMapper = TyCoMapper
, tcm_tyvar = const zonkTcTyVar
, tcm_covar = const (\cv -> mkCoVarCo <$> zonkTyCoVarKind cv)
, tcm_hole = hole
- , tcm_tybinder = \_env tv _vis -> ((), ) <$> zonkTcTyCoVarBndr tv }
+ , tcm_tycobinder = \_env tv _vis -> ((), ) <$> zonkTyCoVarKind tv
+ , tcm_tycon = return }
where
- hole :: () -> CoercionHole -> Role -> Type -> Type
- -> TcM Coercion
- hole _ h r t1 t2
- = do { contents <- unpackCoercionHole_maybe h
+ 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 co h r t1 t2 }
- Nothing -> do { t1 <- zonkTcType t1
- ; t2 <- zonkTcType t2
- ; return $ mkHoleCo h r t1 t2 } }
-
+ 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
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
+-- A tyvar binder is never a unification variable (TauTv),
+-- rather it is always a skolem. It *might* be a TyVarTv.
+-- (Because non-CUSK type declarations use TyVarTvs.)
+-- Regardless, 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
+ | isTyVarTyVar tyvar
+ -- We want to preserve the binding location of the original TyVarTv.
+ -- This is important for error messages. If we don't do this, then
+ -- we get bad locations in, e.g., typecheck/should_fail/T2688
+ = do { zonked_ty <- zonkTcTyVar tyvar
+ ; let zonked_tyvar = tcGetTyVar "zonkTcTyCoVarBndr TyVarTv" zonked_ty
+ zonked_name = getName zonked_tyvar
+ reloc'd_name = setNameLoc zonked_name (getSrcSpan tyvar)
+ ; return (setTyVarName zonked_tyvar reloc'd_name) }
--- | Zonk a TyBinder
-zonkTcTyBinder :: TcTyBinder -> TcM TcTyBinder
-zonkTcTyBinder (Anon ty) = Anon <$> zonkTcType ty
-zonkTcTyBinder (Named tvb) = Named <$> zonkTyVarBinder tvb
-
-zonkTyConBinder :: TyConBinder -> TcM TyConBinder
-zonkTyConBinder = zonkTyVarBinder
+ | otherwise
+ = ASSERT2( isImmutableTyVar tyvar || isCoVar tyvar, pprTyVar tyvar )
+ zonkTyCoVarKind tyvar
-zonkTyVarBinder :: TyVarBndr TyVar vis -> TcM (TyVarBndr TyVar vis)
-zonkTyVarBinder (TvBndr tv vis)
- = do { tv' <- zonkTcTyCoVarBndr tv
- ; return (TvBndr tv' vis) }
+zonkTyConBinders :: [TyConBinder] -> TcM [TyConBinder]
+zonkTyConBinders = mapM zonk1
+ where
+ zonk1 (Bndr tv vis)
+ = do { tv' <- zonkTcTyCoVarBndr tv
+ ; return (Bndr tv' vis) }
zonkTcTyVar :: TcTyVar -> TcM TcType
-- Simply look through all Flexis
= case tcTyVarDetails tv of
SkolemTv {} -> zonk_kind_and_return
RuntimeUnk {} -> zonk_kind_and_return
- FlatSkol ty -> zonkTcType ty
MetaTv { mtv_ref = ref }
-> do { cts <- readMutVar ref
; case cts of
Flexi -> zonk_kind_and_return
- Indirect ty -> zonkTcType ty }
+ Indirect ty -> do { zty <- zonkTcType ty
+ ; writeTcRef ref (Indirect zty)
+ -- See Note [Sharing in zonking]
+ ; return zty } }
| otherwise -- coercion variable
= zonk_kind_and_return
; 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
+-- Should be used only on skolems and TyVarTvs
+zonkTcTyVarToTyVar :: HasDebugCallStack => TcTyVar -> TcM TcTyVar
zonkTcTyVarToTyVar tv
= do { ty <- zonkTcTyVar tv
- ; return (tcGetTyVar "zonkTcTyVarToVar" ty) }
+ ; let tv' = case tcGetTyVar_maybe ty of
+ Just tv' -> tv'
+ Nothing -> pprPanic "zonkTcTyVarToTyVar"
+ (ppr tv $$ ppr ty)
+ ; return tv' }
+
+zonkTyVarTyVarPairs :: [(Name,TcTyVar)] -> TcM [(Name,TcTyVar)]
+zonkTyVarTyVarPairs prs
+ = mapM do_one prs
+ where
+ do_one (nm, tv) = do { tv' <- zonkTcTyVarToTyVar tv
+ ; return (nm, tv') }
+
+{- Note [Sharing in zonking]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Suppose we have
+ alpha :-> beta :-> gamma :-> ty
+where the ":->" means that the unification variable has been
+filled in with Indirect. Then when zonking alpha, it'd be nice
+to short-circuit beta too, so we end up with
+ alpha :-> zty
+ beta :-> zty
+ gamma :-> zty
+where zty is the zonked version of ty. That way, if we come across
+beta later, we'll have less work to do. (And indeed the same for
+alpha.)
+
+This is easily achieved: just overwrite (Indirect ty) with (Indirect
+zty). Non-systematic perf comparisons suggest that this is a modest
+win.
+
+But c.f Note [Sharing when zonking to Type] in TcHsSyn.
-{-
%************************************************************************
%* *
Tidying
zonkTidyTcType env ty = do { ty' <- zonkTcType ty
; return (tidyOpenType env ty') }
--- | Make an 'ErrorThing' storing a type.
-mkTypeErrorThing :: TcType -> ErrorThing
-mkTypeErrorThing ty = ErrorThing ty (Just $ length $ snd $ repSplitAppTys ty)
- zonkTidyTcType
- -- NB: Use *rep*splitAppTys, else we get #11313
-
--- | Make an 'ErrorThing' storing a type, with some extra args known about
-mkTypeErrorThingArgs :: TcType -> Int -> ErrorThing
-mkTypeErrorThingArgs ty num_args
- = ErrorThing ty (Just $ (length $ snd $ repSplitAppTys ty) + num_args)
- zonkTidyTcType
+zonkTidyTcTypes :: TidyEnv -> [TcType] -> TcM (TidyEnv, [TcType])
+zonkTidyTcTypes = zonkTidyTcTypes' []
+ where zonkTidyTcTypes' zs env [] = return (env, reverse zs)
+ zonkTidyTcTypes' zs env (ty:tys)
+ = do { (env', ty') <- zonkTidyTcType env ty
+ ; zonkTidyTcTypes' (ty':zs) env' tys }
zonkTidyOrigin :: TidyEnv -> CtOrigin -> TcM (TidyEnv, CtOrigin)
zonkTidyOrigin env (GivenOrigin skol_info)
; let skol_info2 = tidySkolemInfo env skol_info1
; return (env, GivenOrigin skol_info2) }
zonkTidyOrigin env orig@(TypeEqOrigin { uo_actual = act
- , uo_expected = exp
- , uo_thing = m_thing })
+ , uo_expected = exp })
= do { (env1, act') <- zonkTidyTcType env act
; (env2, exp') <- zonkTidyTcType env1 exp
- ; (env3, m_thing') <- zonkTidyErrorThing env2 m_thing
- ; return ( env3, orig { uo_actual = act'
- , uo_expected = exp'
- , uo_thing = m_thing' }) }
+ ; 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
; return (env3, FunDepOrigin2 p1' o1' p2' l2) }
zonkTidyOrigin env orig = return (env, orig)
-zonkTidyErrorThing :: TidyEnv -> Maybe ErrorThing
- -> TcM (TidyEnv, Maybe ErrorThing)
-zonkTidyErrorThing env (Just (ErrorThing thing n_args zonker))
- = do { (env', thing') <- zonker env thing
- ; return (env', Just $ ErrorThing thing' n_args zonker) }
-zonkTidyErrorThing env Nothing
- = return (env, Nothing)
-
----------------
tidyCt :: TidyEnv -> Ct -> Ct
-- Used only in error reporting
----------------
tidySkolemInfo :: TidyEnv -> SkolemInfo -> SkolemInfo
-tidySkolemInfo env (DerivSkol ty) = DerivSkol (tidyType env ty)
-tidySkolemInfo env (SigSkol cx ty) = SigSkol cx (tidyType env ty)
-tidySkolemInfo env (InferSkol ids) = InferSkol (mapSnd (tidyType env) ids)
-tidySkolemInfo env (UnifyForAllSkol ty) = UnifyForAllSkol (tidyType env ty)
-tidySkolemInfo _ info = info
+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 (tidyTyCoVarOcc env) tv_prs
+ inst_env = mkNameEnv tv_prs'
+
+ tidy_ty env (ForAllTy (Bndr tv vis) ty)
+ = ForAllTy (Bndr 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 -> TyCoVar -> (TidyEnv, TyCoVar)
+ tidy_tv_bndr env@(occ_env, subst) tv
+ | Just tv' <- lookupNameEnv inst_env (tyVarName tv)
+ = ((occ_env, extendVarEnv subst tv tv'), tv')
+
+ | otherwise
+ = tidyVarBndr 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:" <+> pprWithTYPE tidy_ty
+ , text "Kind:" <+> pprWithTYPE tidy_ki ])
+ where
+ (tidy_env, tidy_ty) = tidyOpenType emptyTidyEnv ty
+ tidy_ki = tidyType tidy_env (tcTypeKind ty)
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