{- (c) The University of Glasgow 2006 (c) The GRASP/AQUA Project, Glasgow University, 1992-1998 -} {-# LANGUAGE CPP, ScopedTypeVariables, MultiWayIf, FlexibleContexts #-} {-# OPTIONS_GHC -Wno-incomplete-record-updates #-} -- | Types used in the typechecker -- -- This module provides the Type interface for front-end parts of the -- compiler. These parts -- -- * treat "source types" as opaque: -- newtypes, and predicates are meaningful. -- * look through usage types -- module GHC.Tc.Utils.TcType ( -------------------------------- -- Types TcType, TcSigmaType, TcRhoType, TcTauType, TcPredType, TcThetaType, TcTyVar, TcTyVarSet, TcDTyVarSet, TcTyCoVarSet, TcDTyCoVarSet, TcKind, TcCoVar, TcTyCoVar, TcTyVarBinder, TcInvisTVBinder, TcReqTVBinder, TcTyCon, KnotTied, ExpType(..), InferResult(..), ExpSigmaType, ExpRhoType, mkCheckExpType, SyntaxOpType(..), synKnownType, mkSynFunTys, -- TcLevel TcLevel(..), topTcLevel, pushTcLevel, isTopTcLevel, strictlyDeeperThan, sameDepthAs, tcTypeLevel, tcTyVarLevel, maxTcLevel, promoteSkolem, promoteSkolemX, promoteSkolemsX, -------------------------------- -- MetaDetails TcTyVarDetails(..), pprTcTyVarDetails, vanillaSkolemTv, superSkolemTv, MetaDetails(Flexi, Indirect), MetaInfo(..), isImmutableTyVar, isSkolemTyVar, isMetaTyVar, isMetaTyVarTy, isTyVarTy, tcIsTcTyVar, isTyVarTyVar, isOverlappableTyVar, isTyConableTyVar, isFskTyVar, isFmvTyVar, isFlattenTyVar, isAmbiguousTyVar, metaTyVarRef, metaTyVarInfo, isFlexi, isIndirect, isRuntimeUnkSkol, metaTyVarTcLevel, setMetaTyVarTcLevel, metaTyVarTcLevel_maybe, isTouchableMetaTyVar, isFloatedTouchableMetaTyVar, findDupTyVarTvs, mkTyVarNamePairs, -------------------------------- -- Builders mkPhiTy, mkInfSigmaTy, mkSpecSigmaTy, mkSigmaTy, mkTcAppTy, mkTcAppTys, mkTcCastTy, -------------------------------- -- Splitters -- These are important because they do not look through newtypes getTyVar, tcSplitForAllTy_maybe, tcSplitForAllTys, tcSplitForAllTysReq, tcSplitForAllTysInvis, tcSplitPiTys, tcSplitPiTy_maybe, tcSplitForAllVarBndrs, tcSplitPhiTy, tcSplitPredFunTy_maybe, tcSplitFunTy_maybe, tcSplitFunTys, tcFunArgTy, tcFunResultTy, tcFunResultTyN, tcSplitFunTysN, tcSplitTyConApp, tcSplitTyConApp_maybe, tcTyConAppTyCon, tcTyConAppTyCon_maybe, tcTyConAppArgs, tcSplitAppTy_maybe, tcSplitAppTy, tcSplitAppTys, tcRepSplitAppTy_maybe, tcRepGetNumAppTys, tcGetCastedTyVar_maybe, tcGetTyVar_maybe, tcGetTyVar, tcSplitSigmaTy, tcSplitNestedSigmaTys, --------------------------------- -- Predicates. -- Again, newtypes are opaque eqType, eqTypes, nonDetCmpType, nonDetCmpTypes, eqTypeX, pickyEqType, tcEqType, tcEqKind, tcEqTypeNoKindCheck, tcEqTypeVis, isSigmaTy, isRhoTy, isRhoExpTy, isOverloadedTy, isFloatingTy, isDoubleTy, isFloatTy, isIntTy, isWordTy, isStringTy, isIntegerTy, isNaturalTy, isBoolTy, isUnitTy, isCharTy, isCallStackTy, isCallStackPred, hasIPPred, isTauTy, isTauTyCon, tcIsTyVarTy, tcIsForAllTy, isPredTy, isTyVarClassPred, isTyVarHead, isInsolubleOccursCheck, checkValidClsArgs, hasTyVarHead, isRigidTy, isAlmostFunctionFree, --------------------------------- -- Misc type manipulators deNoteType, orphNamesOfType, orphNamesOfCo, orphNamesOfTypes, orphNamesOfCoCon, getDFunTyKey, evVarPred, --------------------------------- -- Predicate types mkMinimalBySCs, transSuperClasses, pickQuantifiablePreds, pickCapturedPreds, immSuperClasses, boxEqPred, isImprovementPred, -- * Finding type instances tcTyFamInsts, tcTyFamInstsAndVis, tcTyConAppTyFamInstsAndVis, isTyFamFree, -- * Finding "exact" (non-dead) type variables exactTyCoVarsOfType, exactTyCoVarsOfTypes, anyRewritableTyVar, --------------------------------- -- Foreign import and export isFFIArgumentTy, -- :: DynFlags -> Safety -> Type -> Bool isFFIImportResultTy, -- :: DynFlags -> Type -> Bool isFFIExportResultTy, -- :: Type -> Bool isFFIExternalTy, -- :: Type -> Bool isFFIDynTy, -- :: Type -> Type -> Bool isFFIPrimArgumentTy, -- :: DynFlags -> Type -> Bool isFFIPrimResultTy, -- :: DynFlags -> Type -> Bool isFFILabelTy, -- :: Type -> Bool isFFITy, -- :: Type -> Bool isFunPtrTy, -- :: Type -> Bool tcSplitIOType_maybe, -- :: Type -> Maybe Type -------------------------------- -- Reexported from Kind Kind, tcTypeKind, liftedTypeKind, constraintKind, isLiftedTypeKind, isUnliftedTypeKind, classifiesTypeWithValues, -------------------------------- -- Reexported from Type Type, PredType, ThetaType, TyCoBinder, ArgFlag(..), AnonArgFlag(..), mkForAllTy, mkForAllTys, mkInvisForAllTys, mkTyCoInvForAllTys, mkSpecForAllTys, mkTyCoInvForAllTy, mkInfForAllTy, mkInfForAllTys, mkVisFunTy, mkVisFunTys, mkInvisFunTy, mkInvisFunTyMany, mkVisFunTyMany, mkVisFunTysMany, mkInvisFunTysMany, mkTyConApp, mkAppTy, mkAppTys, mkTyConTy, mkTyVarTy, mkTyVarTys, mkTyCoVarTy, mkTyCoVarTys, isClassPred, isEqPrimPred, isIPPred, isEqPred, isEqPredClass, mkClassPred, tcSplitDFunTy, tcSplitDFunHead, tcSplitMethodTy, isRuntimeRepVar, isKindLevPoly, isVisibleBinder, isInvisibleBinder, -- Type substitutions TCvSubst(..), -- Representation visible to a few friends TvSubstEnv, emptyTCvSubst, mkEmptyTCvSubst, zipTvSubst, mkTvSubstPrs, notElemTCvSubst, unionTCvSubst, getTvSubstEnv, setTvSubstEnv, getTCvInScope, extendTCvInScope, extendTCvInScopeList, extendTCvInScopeSet, extendTvSubstAndInScope, Type.lookupTyVar, Type.extendTCvSubst, Type.substTyVarBndr, Type.extendTvSubst, isInScope, mkTCvSubst, mkTvSubst, zipTyEnv, zipCoEnv, Type.substTy, substTys, substScaledTys, substTyWith, substTyWithCoVars, substTyAddInScope, substTyUnchecked, substTysUnchecked, substScaledTyUnchecked, substThetaUnchecked, substTyWithUnchecked, substCoUnchecked, substCoWithUnchecked, substTheta, isUnliftedType, -- Source types are always lifted isUnboxedTupleType, -- Ditto isPrimitiveType, tcView, coreView, tyCoVarsOfType, tyCoVarsOfTypes, closeOverKinds, tyCoFVsOfType, tyCoFVsOfTypes, tyCoVarsOfTypeDSet, tyCoVarsOfTypesDSet, closeOverKindsDSet, tyCoVarsOfTypeList, tyCoVarsOfTypesList, noFreeVarsOfType, -------------------------------- pprKind, pprParendKind, pprSigmaType, pprType, pprParendType, pprTypeApp, pprTyThingCategory, tyThingCategory, pprTheta, pprParendTheta, pprThetaArrowTy, pprClassPred, pprTCvBndr, pprTCvBndrs, TypeSize, sizeType, sizeTypes, scopedSort, --------------------------------- -- argument visibility tcTyConVisibilities, isNextTyConArgVisible, isNextArgVisible ) where #include "HsVersions.h" -- friends: import GHC.Prelude import GHC.Core.TyCo.Rep import GHC.Core.TyCo.Subst ( mkTvSubst, substTyWithCoVars ) import GHC.Core.TyCo.FVs import GHC.Core.TyCo.Ppr import GHC.Core.Class import GHC.Types.Var import GHC.Types.ForeignCall import GHC.Types.Var.Set import GHC.Core.Coercion import GHC.Core.Type as Type import GHC.Core.Predicate import GHC.Types.RepType import GHC.Core.TyCon -- others: import GHC.Driver.Session import GHC.Core.FVs import GHC.Types.Name as Name -- We use this to make dictionaries for type literals. -- Perhaps there's a better way to do this? import GHC.Types.Name.Set import GHC.Types.Var.Env import GHC.Builtin.Names import GHC.Builtin.Types ( coercibleClass, eqClass, heqClass, unitTyCon, unitTyConKey , listTyCon, constraintKind ) import GHC.Types.Basic import GHC.Utils.Misc import GHC.Data.Maybe import GHC.Data.List.SetOps ( getNth, findDupsEq ) import GHC.Utils.Outputable import GHC.Data.FastString import GHC.Utils.Error( Validity(..), MsgDoc, isValid ) import qualified GHC.LanguageExtensions as LangExt import Data.List ( mapAccumL ) -- import Data.Functor.Identity( Identity(..) ) import Data.IORef import Data.List.NonEmpty( NonEmpty(..) ) {- ************************************************************************ * * Types * * ************************************************************************ The type checker divides the generic Type world into the following more structured beasts: sigma ::= forall tyvars. phi -- A sigma type is a qualified type -- -- Note that even if 'tyvars' is empty, theta -- may not be: e.g. (?x::Int) => Int -- Note that 'sigma' is in prenex form: -- all the foralls are at the front. -- A 'phi' type has no foralls to the right of -- an arrow phi :: theta => rho rho ::= sigma -> rho | tau -- A 'tau' type has no quantification anywhere -- Note that the args of a type constructor must be taus tau ::= tyvar | tycon tau_1 .. tau_n | tau_1 tau_2 | tau_1 -> tau_2 -- In all cases, a (saturated) type synonym application is legal, -- provided it expands to the required form. Note [TcTyVars and TyVars in the typechecker] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The typechecker uses a lot of type variables with special properties, notably being a unification variable with a mutable reference. These use the 'TcTyVar' variant of Var.Var. Note, though, that a /bound/ type variable can (and probably should) be a TyVar. E.g forall a. a -> a Here 'a' is really just a deBruijn-number; it certainly does not have a significant TcLevel (as every TcTyVar does). So a forall-bound type variable should be TyVars; and hence a TyVar can appear free in a TcType. The type checker and constraint solver can also encounter /free/ type variables that use the 'TyVar' variant of Var.Var, for a couple of reasons: - When typechecking a class decl, say class C (a :: k) where foo :: T a -> Int We have first kind-check the header; fix k and (a:k) to be TyVars, bring 'k' and 'a' into scope, and kind check the signature for 'foo'. In doing so we call solveEqualities to solve any kind equalities in foo's signature. So the solver may see free occurrences of 'k'. See calls to tcExtendTyVarEnv for other places that ordinary TyVars are bought into scope, and hence may show up in the types and kinds generated by GHC.Tc.Gen.HsType. - The pattern-match overlap checker calls the constraint solver, long after TcTyVars have been zonked away It's convenient to simply treat these TyVars as skolem constants, which of course they are. We give them a level number of "outermost", so they behave as global constants. Specifically: * Var.tcTyVarDetails succeeds on a TyVar, returning vanillaSkolemTv, as well as on a TcTyVar. * tcIsTcTyVar returns True for both TyVar and TcTyVar variants of Var.Var. The "tc" prefix means "a type variable that can be encountered by the typechecker". This is a bit of a change from an earlier era when we remoselessly insisted on real TcTyVars in the type checker. But that seems unnecessary (for skolems, TyVars are fine) and it's now very hard to guarantee, with the advent of kind equalities. Note [Coercion variables in free variable lists] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ There are several places in the GHC codebase where functions like tyCoVarsOfType, tyCoVarsOfCt, et al. are used to compute the free type variables of a type. The "Co" part of these functions' names shouldn't be dismissed, as it is entirely possible that they will include coercion variables in addition to type variables! As a result, there are some places in GHC.Tc.Utils.TcType where we must take care to check that a variable is a _type_ variable (using isTyVar) before calling tcTyVarDetails--a partial function that is not defined for coercion variables--on the variable. Failing to do so led to GHC #12785. -} -- See Note [TcTyVars and TyVars in the typechecker] type TcCoVar = CoVar -- Used only during type inference type TcType = Type -- A TcType can have mutable type variables type TcTyCoVar = Var -- Either a TcTyVar or a CoVar -- Invariant on ForAllTy in TcTypes: -- forall a. T -- a cannot occur inside a MutTyVar in T; that is, -- T is "flattened" before quantifying over a type TcTyVarBinder = TyVarBinder type TcInvisTVBinder = InvisTVBinder type TcReqTVBinder = ReqTVBinder type TcTyCon = TyCon -- these can be the TcTyCon constructor -- These types do not have boxy type variables in them type TcPredType = PredType type TcThetaType = ThetaType type TcSigmaType = TcType type TcRhoType = TcType -- Note [TcRhoType] type TcTauType = TcType type TcKind = Kind type TcTyVarSet = TyVarSet type TcTyCoVarSet = TyCoVarSet type TcDTyVarSet = DTyVarSet type TcDTyCoVarSet = DTyCoVarSet {- ********************************************************************* * * ExpType: an "expected type" in the type checker * * ********************************************************************* -} -- | An expected type to check against during type-checking. -- See Note [ExpType] in "GHC.Tc.Utils.TcMType", where you'll also find manipulators. data ExpType = Check TcType | Infer !InferResult data InferResult = IR { ir_uniq :: Unique -- For debugging only , ir_lvl :: TcLevel -- See Note [TcLevel of ExpType] in GHC.Tc.Utils.TcMType , ir_ref :: IORef (Maybe TcType) } -- The type that fills in this hole should be a Type, -- that is, its kind should be (TYPE rr) for some rr type ExpSigmaType = ExpType type ExpRhoType = ExpType instance Outputable ExpType where ppr (Check ty) = text "Check" <> braces (ppr ty) ppr (Infer ir) = ppr ir instance Outputable InferResult where ppr (IR { ir_uniq = u, ir_lvl = lvl }) = text "Infer" <> braces (ppr u <> comma <> ppr lvl) -- | Make an 'ExpType' suitable for checking. mkCheckExpType :: TcType -> ExpType mkCheckExpType = Check {- ********************************************************************* * * SyntaxOpType * * ********************************************************************* -} -- | What to expect for an argument to a rebindable-syntax operator. -- Quite like 'Type', but allows for holes to be filled in by tcSyntaxOp. -- The callback called from tcSyntaxOp gets a list of types; the meaning -- of these types is determined by a left-to-right depth-first traversal -- of the 'SyntaxOpType' tree. So if you pass in -- -- > SynAny `SynFun` (SynList `SynFun` SynType Int) `SynFun` SynAny -- -- you'll get three types back: one for the first 'SynAny', the /element/ -- type of the list, and one for the last 'SynAny'. You don't get anything -- for the 'SynType', because you've said positively that it should be an -- Int, and so it shall be. -- -- You'll also get three multiplicities back: one for each function arrow. See -- also Note [Linear types] in Multiplicity. -- -- This is defined here to avoid defining it in "GHC.Tc.Gen.Expr" boot file. data SyntaxOpType = SynAny -- ^ Any type | SynRho -- ^ A rho type, skolemised or instantiated as appropriate | SynList -- ^ A list type. You get back the element type of the list | SynFun SyntaxOpType SyntaxOpType -- ^ A function. | SynType ExpType -- ^ A known type. infixr 0 `SynFun` -- | Like 'SynType' but accepts a regular TcType synKnownType :: TcType -> SyntaxOpType synKnownType = SynType . mkCheckExpType -- | Like 'mkFunTys' but for 'SyntaxOpType' mkSynFunTys :: [SyntaxOpType] -> ExpType -> SyntaxOpType mkSynFunTys arg_tys res_ty = foldr SynFun (SynType res_ty) arg_tys {- Note [TcRhoType] ~~~~~~~~~~~~~~~~ A TcRhoType has no foralls or contexts at the top NO forall a. a -> Int NO Eq a => a -> a YES a -> a YES (forall a. a->a) -> Int YES Int -> forall a. a -> Int ************************************************************************ * * TyVarDetails, MetaDetails, MetaInfo * * ************************************************************************ TyVarDetails gives extra info about type variables, used during type checking. It's attached to mutable type variables only. It's knot-tied back to "GHC.Types.Var". There is no reason in principle why "GHC.Types.Var" shouldn't actually have the definition, but it "belongs" here. Note [Signature skolems] ~~~~~~~~~~~~~~~~~~~~~~~~ A TyVarTv is a specialised variant of TauTv, with the following invariants: * A TyVarTv can be unified only with a TyVar, not with any other type * Its MetaDetails, if filled in, will always be another TyVarTv or a SkolemTv TyVarTvs are only distinguished to improve error messages. Consider this data T (a:k1) = MkT (S a) data S (b:k2) = MkS (T b) When doing kind inference on {S,T} we don't want *skolems* for k1,k2, because they end up unifying; we want those TyVarTvs again. Note [TyVars and TcTyVars during type checking] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The Var type has constructors TyVar and TcTyVar. They are used as follows: * TcTyVar: used /only/ during type checking. Should never appear afterwards. May contain a mutable field, in the MetaTv case. * TyVar: is never seen by the constraint solver, except locally inside a type like (forall a. [a] ->[a]), where 'a' is a TyVar. We instantiate these with TcTyVars before exposing the type to the constraint solver. I have swithered about the latter invariant, excluding TyVars from the constraint solver. It's not strictly essential, and indeed (historically but still there) Var.tcTyVarDetails returns vanillaSkolemTv for a TyVar. But ultimately I want to seeparate Type from TcType, and in that case we would need to enforce the separation. -} -- A TyVarDetails is inside a TyVar -- See Note [TyVars and TcTyVars] data TcTyVarDetails = SkolemTv -- A skolem TcLevel -- Level of the implication that binds it -- See GHC.Tc.Utils.Unify Note [Deeper level on the left] for -- how this level number is used Bool -- True <=> this skolem type variable can be overlapped -- when looking up instances -- See Note [Binding when looking up instances] in GHC.Core.InstEnv | RuntimeUnk -- Stands for an as-yet-unknown type in the GHCi -- interactive context | MetaTv { mtv_info :: MetaInfo , mtv_ref :: IORef MetaDetails , mtv_tclvl :: TcLevel } -- See Note [TcLevel and untouchable type variables] vanillaSkolemTv, superSkolemTv :: TcTyVarDetails -- See Note [Binding when looking up instances] in GHC.Core.InstEnv vanillaSkolemTv = SkolemTv topTcLevel False -- Might be instantiated superSkolemTv = SkolemTv topTcLevel True -- Treat this as a completely distinct type -- The choice of level number here is a bit dodgy, but -- topTcLevel works in the places that vanillaSkolemTv is used instance Outputable TcTyVarDetails where ppr = pprTcTyVarDetails pprTcTyVarDetails :: TcTyVarDetails -> SDoc -- For debugging pprTcTyVarDetails (RuntimeUnk {}) = text "rt" pprTcTyVarDetails (SkolemTv lvl True) = text "ssk" <> colon <> ppr lvl pprTcTyVarDetails (SkolemTv lvl False) = text "sk" <> colon <> ppr lvl pprTcTyVarDetails (MetaTv { mtv_info = info, mtv_tclvl = tclvl }) = ppr info <> colon <> ppr tclvl ----------------------------- data MetaDetails = Flexi -- Flexi type variables unify to become Indirects | Indirect TcType data MetaInfo = TauTv -- This MetaTv is an ordinary unification variable -- A TauTv is always filled in with a tau-type, which -- never contains any ForAlls. | TyVarTv -- A variant of TauTv, except that it should not be -- unified with a type, only with a type variable -- See Note [Signature skolems] | FlatMetaTv -- A flatten meta-tyvar -- It is a meta-tyvar, but it is always untouchable, with level 0 -- See Note [The flattening story] in GHC.Tc.Solver.Flatten | FlatSkolTv -- A flatten skolem tyvar -- Just like FlatMetaTv, but is completely "owned" by -- its Given CFunEqCan. -- It is filled in /only/ by unflattenGivens -- See Note [The flattening story] in GHC.Tc.Solver.Flatten instance Outputable MetaDetails where ppr Flexi = text "Flexi" ppr (Indirect ty) = text "Indirect" <+> ppr ty instance Outputable MetaInfo where ppr TauTv = text "tau" ppr TyVarTv = text "tyv" ppr FlatMetaTv = text "fmv" ppr FlatSkolTv = text "fsk" {- ********************************************************************* * * Untouchable type variables * * ********************************************************************* -} newtype TcLevel = TcLevel Int deriving( Eq, Ord ) -- See Note [TcLevel and untouchable type variables] for what this Int is -- See also Note [TcLevel assignment] {- Note [TcLevel and untouchable type variables] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ * Each unification variable (MetaTv) and each Implication has a level number (of type TcLevel) * INVARIANTS. In a tree of Implications, (ImplicInv) The level number (ic_tclvl) of an Implication is STRICTLY GREATER THAN that of its parent (SkolInv) The level number of the skolems (ic_skols) of an Implication is equal to the level of the implication itself (ic_tclvl) (GivenInv) The level number of a unification variable appearing in the 'ic_given' of an implication I should be STRICTLY LESS THAN the ic_tclvl of I (WantedInv) The level number of a unification variable appearing in the 'ic_wanted' of an implication I should be LESS THAN OR EQUAL TO the ic_tclvl of I See Note [WantedInv] * A unification variable is *touchable* if its level number is EQUAL TO that of its immediate parent implication, and it is a TauTv or TyVarTv (but /not/ FlatMetaTv or FlatSkolTv) Note [WantedInv] ~~~~~~~~~~~~~~~~ Why is WantedInv important? Consider this implication, where the constraint (C alpha[3]) disobeys WantedInv: forall[2] a. blah => (C alpha[3]) (forall[3] b. alpha[3] ~ b) We can unify alpha:=b in the inner implication, because 'alpha' is touchable; but then 'b' has excaped its scope into the outer implication. Note [Skolem escape prevention] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ We only unify touchable unification variables. Because of (WantedInv), there can be no occurrences of the variable further out, so the unification can't cause the skolems to escape. Example: data T = forall a. MkT a (a->Int) f x (MkT v f) = length [v,x] We decide (x::alpha), and generate an implication like [1]forall a. (a ~ alpha[0]) But we must not unify alpha:=a, because the skolem would escape. For the cases where we DO want to unify, we rely on floating the equality. Example (with same T) g x (MkT v f) = x && True We decide (x::alpha), and generate an implication like [1]forall a. (Bool ~ alpha[0]) We do NOT unify directly, bur rather float out (if the constraint does not mention 'a') to get (Bool ~ alpha[0]) /\ [1]forall a.() and NOW we can unify alpha. The same idea of only unifying touchables solves another problem. Suppose we had (F Int ~ uf[0]) /\ [1](forall a. C a => F Int ~ beta[1]) In this example, beta is touchable inside the implication. The first solveSimpleWanteds step leaves 'uf' un-unified. Then we move inside the implication where a new constraint uf ~ beta emerges. If we (wrongly) spontaneously solved it to get uf := beta, the whole implication disappears but when we pop out again we are left with (F Int ~ uf) which will be unified by our final zonking stage and uf will get unified *once more* to (F Int). Note [TcLevel assignment] ~~~~~~~~~~~~~~~~~~~~~~~~~ We arrange the TcLevels like this 0 Top level 1 First-level implication constraints 2 Second-level implication constraints ...etc... -} maxTcLevel :: TcLevel -> TcLevel -> TcLevel maxTcLevel (TcLevel a) (TcLevel b) = TcLevel (a `max` b) topTcLevel :: TcLevel -- See Note [TcLevel assignment] topTcLevel = TcLevel 0 -- 0 = outermost level isTopTcLevel :: TcLevel -> Bool isTopTcLevel (TcLevel 0) = True isTopTcLevel _ = False pushTcLevel :: TcLevel -> TcLevel -- See Note [TcLevel assignment] pushTcLevel (TcLevel us) = TcLevel (us + 1) strictlyDeeperThan :: TcLevel -> TcLevel -> Bool strictlyDeeperThan (TcLevel tv_tclvl) (TcLevel ctxt_tclvl) = tv_tclvl > ctxt_tclvl sameDepthAs :: TcLevel -> TcLevel -> Bool sameDepthAs (TcLevel ctxt_tclvl) (TcLevel tv_tclvl) = ctxt_tclvl == tv_tclvl -- NB: invariant ctxt_tclvl >= tv_tclvl -- So <= would be equivalent checkTcLevelInvariant :: TcLevel -> TcLevel -> Bool -- Checks (WantedInv) from Note [TcLevel and untouchable type variables] checkTcLevelInvariant (TcLevel ctxt_tclvl) (TcLevel tv_tclvl) = ctxt_tclvl >= tv_tclvl -- Returns topTcLevel for non-TcTyVars tcTyVarLevel :: TcTyVar -> TcLevel tcTyVarLevel tv = case tcTyVarDetails tv of MetaTv { mtv_tclvl = tv_lvl } -> tv_lvl SkolemTv tv_lvl _ -> tv_lvl RuntimeUnk -> topTcLevel tcTypeLevel :: TcType -> TcLevel -- Max level of any free var of the type tcTypeLevel ty = nonDetStrictFoldDVarSet add topTcLevel (tyCoVarsOfTypeDSet ty) -- It's safe to use a non-deterministic fold because `maxTcLevel` is -- commutative. where add v lvl | isTcTyVar v = lvl `maxTcLevel` tcTyVarLevel v | otherwise = lvl instance Outputable TcLevel where ppr (TcLevel us) = ppr us promoteSkolem :: TcLevel -> TcTyVar -> TcTyVar promoteSkolem tclvl skol | tclvl < tcTyVarLevel skol = ASSERT( isTcTyVar skol && isSkolemTyVar skol ) setTcTyVarDetails skol (SkolemTv tclvl (isOverlappableTyVar skol)) | otherwise = skol -- | Change the TcLevel in a skolem, extending a substitution promoteSkolemX :: TcLevel -> TCvSubst -> TcTyVar -> (TCvSubst, TcTyVar) promoteSkolemX tclvl subst skol = ASSERT( isTcTyVar skol && isSkolemTyVar skol ) (new_subst, new_skol) where new_skol | tclvl < tcTyVarLevel skol = setTcTyVarDetails (updateTyVarKind (substTy subst) skol) (SkolemTv tclvl (isOverlappableTyVar skol)) | otherwise = updateTyVarKind (substTy subst) skol new_subst = extendTvSubstWithClone subst skol new_skol promoteSkolemsX :: TcLevel -> TCvSubst -> [TcTyVar] -> (TCvSubst, [TcTyVar]) promoteSkolemsX tclvl = mapAccumL (promoteSkolemX tclvl) {- ********************************************************************* * * Finding type family instances * * ************************************************************************ -} -- | Finds outermost type-family applications occurring in a type, -- after expanding synonyms. In the list (F, tys) that is returned -- we guarantee that tys matches F's arity. For example, given -- type family F a :: * -> * (arity 1) -- calling tcTyFamInsts on (Maybe (F Int Bool) will return -- (F, [Int]), not (F, [Int,Bool]) -- -- This is important for its use in deciding termination of type -- instances (see #11581). E.g. -- type instance G [Int] = ...(F Int \<big type>)... -- we don't need to take \<big type> into account when asking if -- the calls on the RHS are smaller than the LHS tcTyFamInsts :: Type -> [(TyCon, [Type])] tcTyFamInsts = map (\(_,b,c) -> (b,c)) . tcTyFamInstsAndVis -- | Like 'tcTyFamInsts', except that the output records whether the -- type family and its arguments occur as an /invisible/ argument in -- some type application. This information is useful because it helps GHC know -- when to turn on @-fprint-explicit-kinds@ during error reporting so that -- users can actually see the type family being mentioned. -- -- As an example, consider: -- -- @ -- class C a -- data T (a :: k) -- type family F a :: k -- instance C (T @(F Int) (F Bool)) -- @ -- -- There are two occurrences of the type family `F` in that `C` instance, so -- @'tcTyFamInstsAndVis' (C (T \@(F Int) (F Bool)))@ will return: -- -- @ -- [ ('True', F, [Int]) -- , ('False', F, [Bool]) ] -- @ -- -- @F Int@ is paired with 'True' since it appears as an /invisible/ argument -- to @C@, whereas @F Bool@ is paired with 'False' since it appears an a -- /visible/ argument to @C@. -- -- See also @Note [Kind arguments in error messages]@ in "GHC.Tc.Errors". tcTyFamInstsAndVis :: Type -> [(Bool, TyCon, [Type])] tcTyFamInstsAndVis = tcTyFamInstsAndVisX False tcTyFamInstsAndVisX :: Bool -- ^ Is this an invisible argument to some type application? -> Type -> [(Bool, TyCon, [Type])] tcTyFamInstsAndVisX = go where go is_invis_arg ty | Just exp_ty <- tcView ty = go is_invis_arg exp_ty go _ (TyVarTy _) = [] go is_invis_arg (TyConApp tc tys) | isTypeFamilyTyCon tc = [(is_invis_arg, tc, take (tyConArity tc) tys)] | otherwise = tcTyConAppTyFamInstsAndVisX is_invis_arg tc tys go _ (LitTy {}) = [] go is_invis_arg (ForAllTy bndr ty) = go is_invis_arg (binderType bndr) ++ go is_invis_arg ty go is_invis_arg (FunTy _ w ty1 ty2) = go is_invis_arg w ++ go is_invis_arg ty1 ++ go is_invis_arg ty2 go is_invis_arg ty@(AppTy _ _) = let (ty_head, ty_args) = splitAppTys ty ty_arg_flags = appTyArgFlags ty_head ty_args in go is_invis_arg ty_head ++ concat (zipWith (\flag -> go (isInvisibleArgFlag flag)) ty_arg_flags ty_args) go is_invis_arg (CastTy ty _) = go is_invis_arg ty go _ (CoercionTy _) = [] -- don't count tyfams in coercions, -- as they never get normalized, -- anyway -- | In an application of a 'TyCon' to some arguments, find the outermost -- occurrences of type family applications within the arguments. This function -- will not consider the 'TyCon' itself when checking for type family -- applications. -- -- See 'tcTyFamInstsAndVis' for more details on how this works (as this -- function is called inside of 'tcTyFamInstsAndVis'). tcTyConAppTyFamInstsAndVis :: TyCon -> [Type] -> [(Bool, TyCon, [Type])] tcTyConAppTyFamInstsAndVis = tcTyConAppTyFamInstsAndVisX False tcTyConAppTyFamInstsAndVisX :: Bool -- ^ Is this an invisible argument to some type application? -> TyCon -> [Type] -> [(Bool, TyCon, [Type])] tcTyConAppTyFamInstsAndVisX is_invis_arg tc tys = let (invis_tys, vis_tys) = partitionInvisibleTypes tc tys in concat $ map (tcTyFamInstsAndVisX True) invis_tys ++ map (tcTyFamInstsAndVisX is_invis_arg) vis_tys isTyFamFree :: Type -> Bool -- ^ Check that a type does not contain any type family applications. isTyFamFree = null . tcTyFamInsts anyRewritableTyVar :: Bool -- Ignore casts and coercions -> EqRel -- Ambient role -> (EqRel -> TcTyVar -> Bool) -> TcType -> Bool -- (anyRewritableTyVar ignore_cos pred ty) returns True -- if the 'pred' returns True of any free TyVar in 'ty' -- Do not look inside casts and coercions if 'ignore_cos' is True -- See Note [anyRewritableTyVar must be role-aware] anyRewritableTyVar ignore_cos role pred ty = go role emptyVarSet ty where -- NB: No need to expand synonyms, because we can find -- all free variables of a synonym by looking at its -- arguments go_tv rl bvs tv | tv `elemVarSet` bvs = False | otherwise = pred rl tv go rl bvs (TyVarTy tv) = go_tv rl bvs tv go _ _ (LitTy {}) = False go rl bvs (TyConApp tc tys) = go_tc rl bvs tc tys go rl bvs (AppTy fun arg) = go rl bvs fun || go NomEq bvs arg go rl bvs (FunTy _ w arg res) = go NomEq bvs arg_rep || go NomEq bvs res_rep || go rl bvs arg || go rl bvs res || go NomEq bvs w where arg_rep = getRuntimeRep arg -- forgetting these causes #17024 res_rep = getRuntimeRep res go rl bvs (ForAllTy tv ty) = go rl (bvs `extendVarSet` binderVar tv) ty go rl bvs (CastTy ty co) = go rl bvs ty || go_co rl bvs co go rl bvs (CoercionTy co) = go_co rl bvs co -- ToDo: check go_tc NomEq bvs _ tys = any (go NomEq bvs) tys go_tc ReprEq bvs tc tys = any (go_arg bvs) (tyConRolesRepresentational tc `zip` tys) go_arg bvs (Nominal, ty) = go NomEq bvs ty go_arg bvs (Representational, ty) = go ReprEq bvs ty go_arg _ (Phantom, _) = False -- We never rewrite with phantoms go_co rl bvs co | ignore_cos = False | otherwise = anyVarSet (go_tv rl bvs) (tyCoVarsOfCo co) -- We don't have an equivalent of anyRewritableTyVar for coercions -- (at least not yet) so take the free vars and test them {- Note [anyRewritableTyVar must be role-aware] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ anyRewritableTyVar is used during kick-out from the inert set, to decide if, given a new equality (a ~ ty), we should kick out a constraint C. Rather than gather free variables and see if 'a' is among them, we instead pass in a predicate; this is just efficiency. Moreover, consider work item: [G] a ~R f b inert item: [G] b ~R f a We use anyRewritableTyVar to decide whether to kick out the inert item, on the grounds that the work item might rewrite it. Well, 'a' is certainly free in [G] b ~R f a. But because the role of a type variable ('f' in this case) is nominal, the work item can't actually rewrite the inert item. Moreover, if we were to kick out the inert item the exact same situation would re-occur and we end up with an infinite loop in which each kicks out the other (#14363). -} {- ********************************************************************* * * The "exact" free variables of a type * * ********************************************************************* -} {- Note [Silly type synonym] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Consider type T a = Int What are the free tyvars of (T x)? Empty, of course! exactTyCoVarsOfType is used by the type checker to figure out exactly which type variables are mentioned in a type. It only matters occasionally -- see the calls to exactTyCoVarsOfType. We place this function here in GHC.Tc.Utils.TcType, not in GHC.Core.TyCo.FVs, because we want to "see" tcView (efficiency issue only). -} exactTyCoVarsOfType :: Type -> TyCoVarSet exactTyCoVarsOfTypes :: [Type] -> TyCoVarSet -- Find the free type variables (of any kind) -- but *expand* type synonyms. See Note [Silly type synonym] above. exactTyCoVarsOfType ty = runTyCoVars (exact_ty ty) exactTyCoVarsOfTypes tys = runTyCoVars (exact_tys tys) exact_ty :: Type -> Endo TyCoVarSet exact_tys :: [Type] -> Endo TyCoVarSet (exact_ty, exact_tys, _, _) = foldTyCo exactTcvFolder emptyVarSet exactTcvFolder :: TyCoFolder TyCoVarSet (Endo TyCoVarSet) exactTcvFolder = deepTcvFolder { tcf_view = tcView } -- This is the key line {- ************************************************************************ * * Predicates * * ************************************************************************ -} tcIsTcTyVar :: TcTyVar -> Bool -- See Note [TcTyVars and TyVars in the typechecker] tcIsTcTyVar tv = isTyVar tv isTouchableMetaTyVar :: TcLevel -> TcTyVar -> Bool isTouchableMetaTyVar ctxt_tclvl tv | isTyVar tv -- See Note [Coercion variables in free variable lists] , MetaTv { mtv_tclvl = tv_tclvl, mtv_info = info } <- tcTyVarDetails tv , not (isFlattenInfo info) = ASSERT2( checkTcLevelInvariant ctxt_tclvl tv_tclvl, ppr tv $$ ppr tv_tclvl $$ ppr ctxt_tclvl ) tv_tclvl `sameDepthAs` ctxt_tclvl | otherwise = False isFloatedTouchableMetaTyVar :: TcLevel -> TcTyVar -> Bool isFloatedTouchableMetaTyVar ctxt_tclvl tv | isTyVar tv -- See Note [Coercion variables in free variable lists] , MetaTv { mtv_tclvl = tv_tclvl, mtv_info = info } <- tcTyVarDetails tv , not (isFlattenInfo info) = tv_tclvl `strictlyDeeperThan` ctxt_tclvl | otherwise = False isImmutableTyVar :: TyVar -> Bool isImmutableTyVar tv = isSkolemTyVar tv isTyConableTyVar, isSkolemTyVar, isOverlappableTyVar, isMetaTyVar, isAmbiguousTyVar, isFmvTyVar, isFskTyVar, isFlattenTyVar :: TcTyVar -> Bool isTyConableTyVar tv -- True of a meta-type variable that can be filled in -- with a type constructor application; in particular, -- not a TyVarTv | isTyVar tv -- See Note [Coercion variables in free variable lists] = case tcTyVarDetails tv of MetaTv { mtv_info = TyVarTv } -> False _ -> True | otherwise = True isFmvTyVar tv = ASSERT2( tcIsTcTyVar tv, ppr tv ) case tcTyVarDetails tv of MetaTv { mtv_info = FlatMetaTv } -> True _ -> False isFskTyVar tv = ASSERT2( tcIsTcTyVar tv, ppr tv ) case tcTyVarDetails tv of MetaTv { mtv_info = FlatSkolTv } -> True _ -> False -- | True of both given and wanted flatten-skolems (fmv and fsk) isFlattenTyVar tv = ASSERT2( tcIsTcTyVar tv, ppr tv ) case tcTyVarDetails tv of MetaTv { mtv_info = info } -> isFlattenInfo info _ -> False isSkolemTyVar tv = ASSERT2( tcIsTcTyVar tv, ppr tv ) case tcTyVarDetails tv of MetaTv {} -> False _other -> True isOverlappableTyVar tv | isTyVar tv -- See Note [Coercion variables in free variable lists] = case tcTyVarDetails tv of SkolemTv _ overlappable -> overlappable _ -> False | otherwise = False isMetaTyVar tv | isTyVar tv -- See Note [Coercion variables in free variable lists] = case tcTyVarDetails tv of MetaTv {} -> True _ -> False | otherwise = False -- isAmbiguousTyVar is used only when reporting type errors -- It picks out variables that are unbound, namely meta -- type variables and the RuntimUnk variables created by -- GHC.Runtime.Heap.Inspect.zonkRTTIType. These are "ambiguous" in -- the sense that they stand for an as-yet-unknown type isAmbiguousTyVar tv | isTyVar tv -- See Note [Coercion variables in free variable lists] = case tcTyVarDetails tv of MetaTv {} -> True RuntimeUnk {} -> True _ -> False | otherwise = False isMetaTyVarTy :: TcType -> Bool isMetaTyVarTy (TyVarTy tv) = isMetaTyVar tv isMetaTyVarTy _ = False metaTyVarInfo :: TcTyVar -> MetaInfo metaTyVarInfo tv = case tcTyVarDetails tv of MetaTv { mtv_info = info } -> info _ -> pprPanic "metaTyVarInfo" (ppr tv) isFlattenInfo :: MetaInfo -> Bool isFlattenInfo FlatMetaTv = True isFlattenInfo FlatSkolTv = True isFlattenInfo _ = False metaTyVarTcLevel :: TcTyVar -> TcLevel metaTyVarTcLevel tv = case tcTyVarDetails tv of MetaTv { mtv_tclvl = tclvl } -> tclvl _ -> pprPanic "metaTyVarTcLevel" (ppr tv) metaTyVarTcLevel_maybe :: TcTyVar -> Maybe TcLevel metaTyVarTcLevel_maybe tv = case tcTyVarDetails tv of MetaTv { mtv_tclvl = tclvl } -> Just tclvl _ -> Nothing metaTyVarRef :: TyVar -> IORef MetaDetails metaTyVarRef tv = case tcTyVarDetails tv of MetaTv { mtv_ref = ref } -> ref _ -> pprPanic "metaTyVarRef" (ppr tv) setMetaTyVarTcLevel :: TcTyVar -> TcLevel -> TcTyVar setMetaTyVarTcLevel tv tclvl = case tcTyVarDetails tv of details@(MetaTv {}) -> setTcTyVarDetails tv (details { mtv_tclvl = tclvl }) _ -> pprPanic "metaTyVarTcLevel" (ppr tv) isTyVarTyVar :: Var -> Bool isTyVarTyVar tv = case tcTyVarDetails tv of MetaTv { mtv_info = TyVarTv } -> True _ -> False isFlexi, isIndirect :: MetaDetails -> Bool isFlexi Flexi = True isFlexi _ = False isIndirect (Indirect _) = True isIndirect _ = False isRuntimeUnkSkol :: TyVar -> Bool -- Called only in GHC.Tc.Errors; see Note [Runtime skolems] there isRuntimeUnkSkol x | RuntimeUnk <- tcTyVarDetails x = True | otherwise = False mkTyVarNamePairs :: [TyVar] -> [(Name,TyVar)] -- Just pair each TyVar with its own name mkTyVarNamePairs tvs = [(tyVarName tv, tv) | tv <- tvs] findDupTyVarTvs :: [(Name,TcTyVar)] -> [(Name,Name)] -- If we have [...(x1,tv)...(x2,tv)...] -- return (x1,x2) in the result list findDupTyVarTvs prs = concatMap mk_result_prs $ findDupsEq eq_snd prs where eq_snd (_,tv1) (_,tv2) = tv1 == tv2 mk_result_prs ((n1,_) :| xs) = map (\(n2,_) -> (n1,n2)) xs {- ************************************************************************ * * Tau, sigma and rho * * ************************************************************************ -} mkSigmaTy :: [TyCoVarBinder] -> [PredType] -> Type -> Type mkSigmaTy bndrs theta tau = mkForAllTys bndrs (mkPhiTy theta tau) -- | Make a sigma ty where all type variables are 'Inferred'. That is, -- they cannot be used with visible type application. mkInfSigmaTy :: [TyCoVar] -> [PredType] -> Type -> Type mkInfSigmaTy tyvars theta ty = mkSigmaTy (mkTyCoVarBinders Inferred tyvars) theta ty -- | Make a sigma ty where all type variables are "specified". That is, -- they can be used with visible type application mkSpecSigmaTy :: [TyVar] -> [PredType] -> Type -> Type mkSpecSigmaTy tyvars preds ty = mkSigmaTy (mkTyCoVarBinders Specified tyvars) preds ty mkPhiTy :: [PredType] -> Type -> Type mkPhiTy = mkInvisFunTysMany --------------- getDFunTyKey :: Type -> OccName -- Get some string from a type, to be used to -- construct a dictionary function name getDFunTyKey ty | Just ty' <- coreView ty = getDFunTyKey ty' getDFunTyKey (TyVarTy tv) = getOccName tv getDFunTyKey (TyConApp tc _) = getOccName tc getDFunTyKey (LitTy x) = getDFunTyLitKey x getDFunTyKey (AppTy fun _) = getDFunTyKey fun getDFunTyKey (FunTy {}) = getOccName funTyCon getDFunTyKey (ForAllTy _ t) = getDFunTyKey t getDFunTyKey (CastTy ty _) = getDFunTyKey ty getDFunTyKey t@(CoercionTy _) = pprPanic "getDFunTyKey" (ppr t) getDFunTyLitKey :: TyLit -> OccName getDFunTyLitKey (NumTyLit n) = mkOccName Name.varName (show n) getDFunTyLitKey (StrTyLit n) = mkOccName Name.varName (show n) -- hm {- ********************************************************************* * * Building types * * ********************************************************************* -} -- ToDo: I think we need Tc versions of these -- Reason: mkCastTy checks isReflexiveCastTy, which checks -- for equality; and that has a different answer -- depending on whether or not Type = Constraint mkTcAppTys :: Type -> [Type] -> Type mkTcAppTys = mkAppTys mkTcAppTy :: Type -> Type -> Type mkTcAppTy = mkAppTy mkTcCastTy :: Type -> Coercion -> Type mkTcCastTy = mkCastTy -- Do we need a tc version of mkCastTy? {- ************************************************************************ * * Expanding and splitting * * ************************************************************************ These tcSplit functions are like their non-Tc analogues, but *) they do not look through newtypes However, they are non-monadic and do not follow through mutable type variables. It's up to you to make sure this doesn't matter. -} -- | Splits a forall type into a list of 'TyBinder's and the inner type. -- Always succeeds, even if it returns an empty list. tcSplitPiTys :: Type -> ([TyBinder], Type) tcSplitPiTys ty = ASSERT( all isTyBinder (fst sty) ) sty where sty = splitPiTys ty -- | Splits a type into a TyBinder and a body, if possible. Panics otherwise tcSplitPiTy_maybe :: Type -> Maybe (TyBinder, Type) tcSplitPiTy_maybe ty = ASSERT( isMaybeTyBinder sty ) sty where sty = splitPiTy_maybe ty isMaybeTyBinder (Just (t,_)) = isTyBinder t isMaybeTyBinder _ = True tcSplitForAllTy_maybe :: Type -> Maybe (TyVarBinder, Type) tcSplitForAllTy_maybe ty | Just ty' <- tcView ty = tcSplitForAllTy_maybe ty' tcSplitForAllTy_maybe (ForAllTy tv ty) = ASSERT( isTyVarBinder tv ) Just (tv, ty) tcSplitForAllTy_maybe _ = Nothing -- | Like 'tcSplitPiTys', but splits off only named binders, -- returning just the tycovars. tcSplitForAllTys :: Type -> ([TyVar], Type) tcSplitForAllTys ty = ASSERT( all isTyVar (fst sty) ) sty where sty = splitForAllTys ty -- | Like 'tcSplitForAllTys', but only splits 'ForAllTy's with 'Required' type -- variable binders. All split tyvars are annotated with '()'. tcSplitForAllTysReq :: Type -> ([TcReqTVBinder], Type) tcSplitForAllTysReq ty = ASSERT( all (isTyVar . binderVar) (fst sty) ) sty where sty = splitForAllTysReq ty -- | Like 'tcSplitForAllTys', but only splits 'ForAllTy's with 'Invisible' type -- variable binders. All split tyvars are annotated with their 'Specificity'. tcSplitForAllTysInvis :: Type -> ([TcInvisTVBinder], Type) tcSplitForAllTysInvis ty = ASSERT( all (isTyVar . binderVar) (fst sty) ) sty where sty = splitForAllTysInvis ty -- | Like 'tcSplitForAllTys', but splits off only named binders. tcSplitForAllVarBndrs :: Type -> ([TyVarBinder], Type) tcSplitForAllVarBndrs ty = ASSERT( all isTyVarBinder (fst sty)) sty where sty = splitForAllVarBndrs ty -- | Is this a ForAllTy with a named binder? tcIsForAllTy :: Type -> Bool tcIsForAllTy ty | Just ty' <- tcView ty = tcIsForAllTy ty' tcIsForAllTy (ForAllTy {}) = True tcIsForAllTy _ = False tcSplitPredFunTy_maybe :: Type -> Maybe (PredType, Type) -- Split off the first predicate argument from a type tcSplitPredFunTy_maybe ty | Just ty' <- tcView ty = tcSplitPredFunTy_maybe ty' tcSplitPredFunTy_maybe (FunTy { ft_af = InvisArg , ft_arg = arg, ft_res = res }) = Just (arg, res) tcSplitPredFunTy_maybe _ = Nothing tcSplitPhiTy :: Type -> (ThetaType, Type) tcSplitPhiTy ty = split ty [] where split ty ts = case tcSplitPredFunTy_maybe ty of Just (pred, ty) -> split ty (pred:ts) Nothing -> (reverse ts, ty) -- | Split a sigma type into its parts. tcSplitSigmaTy :: Type -> ([TyVar], ThetaType, Type) tcSplitSigmaTy ty = case tcSplitForAllTys ty of (tvs, rho) -> case tcSplitPhiTy rho of (theta, tau) -> (tvs, theta, tau) -- | Split a sigma type into its parts, going underneath as many @ForAllTy@s -- as possible. For example, given this type synonym: -- -- @ -- type Traversal s t a b = forall f. Applicative f => (a -> f b) -> s -> f t -- @ -- -- if you called @tcSplitSigmaTy@ on this type: -- -- @ -- forall s t a b. Each s t a b => Traversal s t a b -- @ -- -- then it would return @([s,t,a,b], [Each s t a b], Traversal s t a b)@. But -- if you instead called @tcSplitNestedSigmaTys@ on the type, it would return -- @([s,t,a,b,f], [Each s t a b, Applicative f], (a -> f b) -> s -> f t)@. tcSplitNestedSigmaTys :: Type -> ([TyVar], ThetaType, Type) -- NB: This is basically a pure version of topInstantiate (from Inst) that -- doesn't compute an HsWrapper. tcSplitNestedSigmaTys ty -- If there's a forall, split it apart and try splitting the rho type -- underneath it. | (tvs1, theta1, rho1) <- tcSplitSigmaTy ty , not (null tvs1 && null theta1) = let (tvs2, theta2, rho2) = tcSplitNestedSigmaTys rho1 in (tvs1 ++ tvs2, theta1 ++ theta2, rho2) -- If there's no forall, we're done. | otherwise = ([], [], ty) ----------------------- tcTyConAppTyCon :: Type -> TyCon tcTyConAppTyCon ty = case tcTyConAppTyCon_maybe ty of Just tc -> tc Nothing -> pprPanic "tcTyConAppTyCon" (pprType ty) -- | Like 'tcRepSplitTyConApp_maybe', but only returns the 'TyCon'. tcTyConAppTyCon_maybe :: Type -> Maybe TyCon tcTyConAppTyCon_maybe ty | Just ty' <- tcView ty = tcTyConAppTyCon_maybe ty' tcTyConAppTyCon_maybe (TyConApp tc _) = Just tc tcTyConAppTyCon_maybe (FunTy { ft_af = VisArg }) = Just funTyCon -- (=>) is /not/ a TyCon in its own right -- C.f. tcRepSplitAppTy_maybe tcTyConAppTyCon_maybe _ = Nothing tcTyConAppArgs :: Type -> [Type] tcTyConAppArgs ty = case tcSplitTyConApp_maybe ty of Just (_, args) -> args Nothing -> pprPanic "tcTyConAppArgs" (pprType ty) tcSplitTyConApp :: Type -> (TyCon, [Type]) tcSplitTyConApp ty = case tcSplitTyConApp_maybe ty of Just stuff -> stuff Nothing -> pprPanic "tcSplitTyConApp" (pprType ty) ----------------------- tcSplitFunTys :: Type -> ([Scaled Type], Type) tcSplitFunTys ty = case tcSplitFunTy_maybe ty of Nothing -> ([], ty) Just (arg,res) -> (arg:args, res') where (args,res') = tcSplitFunTys res tcSplitFunTy_maybe :: Type -> Maybe (Scaled Type, Type) tcSplitFunTy_maybe ty | Just ty' <- tcView ty = tcSplitFunTy_maybe ty' tcSplitFunTy_maybe (FunTy { ft_af = af, ft_mult = w, ft_arg = arg, ft_res = res }) | VisArg <- af = Just (Scaled w arg, res) tcSplitFunTy_maybe _ = Nothing -- Note the VisArg guard -- Consider (?x::Int) => Bool -- We don't want to treat this as a function type! -- A concrete example is test tc230: -- f :: () -> (?p :: ()) => () -> () -- -- g = f () () tcSplitFunTysN :: Arity -- n: Number of desired args -> TcRhoType -> Either Arity -- Number of missing arrows ([Scaled TcSigmaType],-- Arg types (always N types) TcSigmaType) -- The rest of the type -- ^ Split off exactly the specified number argument types -- Returns -- (Left m) if there are 'm' missing arrows in the type -- (Right (tys,res)) if the type looks like t1 -> ... -> tn -> res tcSplitFunTysN n ty | n == 0 = Right ([], ty) | Just (arg,res) <- tcSplitFunTy_maybe ty = case tcSplitFunTysN (n-1) res of Left m -> Left m Right (args,body) -> Right (arg:args, body) | otherwise = Left n tcSplitFunTy :: Type -> (Scaled Type, Type) tcSplitFunTy ty = expectJust "tcSplitFunTy" (tcSplitFunTy_maybe ty) tcFunArgTy :: Type -> Scaled Type tcFunArgTy ty = fst (tcSplitFunTy ty) tcFunResultTy :: Type -> Type tcFunResultTy ty = snd (tcSplitFunTy ty) -- | Strips off n *visible* arguments and returns the resulting type tcFunResultTyN :: HasDebugCallStack => Arity -> Type -> Type tcFunResultTyN n ty | Right (_, res_ty) <- tcSplitFunTysN n ty = res_ty | otherwise = pprPanic "tcFunResultTyN" (ppr n <+> ppr ty) ----------------------- tcSplitAppTy_maybe :: Type -> Maybe (Type, Type) tcSplitAppTy_maybe ty | Just ty' <- tcView ty = tcSplitAppTy_maybe ty' tcSplitAppTy_maybe ty = tcRepSplitAppTy_maybe ty tcSplitAppTy :: Type -> (Type, Type) tcSplitAppTy ty = case tcSplitAppTy_maybe ty of Just stuff -> stuff Nothing -> pprPanic "tcSplitAppTy" (pprType ty) tcSplitAppTys :: Type -> (Type, [Type]) tcSplitAppTys ty = go ty [] where go ty args = case tcSplitAppTy_maybe ty of Just (ty', arg) -> go ty' (arg:args) Nothing -> (ty,args) -- | Returns the number of arguments in the given type, without -- looking through synonyms. This is used only for error reporting. -- We don't look through synonyms because of #11313. tcRepGetNumAppTys :: Type -> Arity tcRepGetNumAppTys = length . snd . repSplitAppTys ----------------------- -- | If the type is a tyvar, possibly under a cast, returns it, along -- with the coercion. Thus, the co is :: kind tv ~N kind type tcGetCastedTyVar_maybe :: Type -> Maybe (TyVar, CoercionN) tcGetCastedTyVar_maybe ty | Just ty' <- tcView ty = tcGetCastedTyVar_maybe ty' tcGetCastedTyVar_maybe (CastTy (TyVarTy tv) co) = Just (tv, co) tcGetCastedTyVar_maybe (TyVarTy tv) = Just (tv, mkNomReflCo (tyVarKind tv)) tcGetCastedTyVar_maybe _ = Nothing tcGetTyVar_maybe :: Type -> Maybe TyVar tcGetTyVar_maybe ty | Just ty' <- tcView ty = tcGetTyVar_maybe ty' tcGetTyVar_maybe (TyVarTy tv) = Just tv tcGetTyVar_maybe _ = Nothing tcGetTyVar :: String -> Type -> TyVar tcGetTyVar msg ty = case tcGetTyVar_maybe ty of Just tv -> tv Nothing -> pprPanic msg (ppr ty) tcIsTyVarTy :: Type -> Bool tcIsTyVarTy ty | Just ty' <- tcView ty = tcIsTyVarTy ty' tcIsTyVarTy (CastTy ty _) = tcIsTyVarTy ty -- look through casts, as -- this is only used for -- e.g., FlexibleContexts tcIsTyVarTy (TyVarTy _) = True tcIsTyVarTy _ = False ----------------------- tcSplitDFunTy :: Type -> ([TyVar], [Type], Class, [Type]) -- Split the type of a dictionary function -- We don't use tcSplitSigmaTy, because a DFun may (with NDP) -- have non-Pred arguments, such as -- df :: forall m. (forall b. Eq b => Eq (m b)) -> C m -- -- Also NB splitFunTys, not tcSplitFunTys; -- the latter specifically stops at PredTy arguments, -- and we don't want to do that here tcSplitDFunTy ty = case tcSplitForAllTys ty of { (tvs, rho) -> case splitFunTys rho of { (theta, tau) -> case tcSplitDFunHead tau of { (clas, tys) -> (tvs, map scaledThing theta, clas, tys) }}} tcSplitDFunHead :: Type -> (Class, [Type]) tcSplitDFunHead = getClassPredTys tcSplitMethodTy :: Type -> ([TyVar], PredType, Type) -- A class method (selector) always has a type like -- forall as. C as => blah -- So if the class looks like -- class C a where -- op :: forall b. (Eq a, Ix b) => a -> b -- the class method type looks like -- op :: forall a. C a => forall b. (Eq a, Ix b) => a -> b -- -- tcSplitMethodTy just peels off the outer forall and -- that first predicate tcSplitMethodTy ty | (sel_tyvars,sel_rho) <- tcSplitForAllTys ty , Just (first_pred, local_meth_ty) <- tcSplitPredFunTy_maybe sel_rho = (sel_tyvars, first_pred, local_meth_ty) | otherwise = pprPanic "tcSplitMethodTy" (ppr ty) {- ********************************************************************* * * Type equalities * * ********************************************************************* -} tcEqKind :: HasDebugCallStack => TcKind -> TcKind -> Bool tcEqKind = tcEqType tcEqType :: HasDebugCallStack => TcType -> TcType -> Bool -- tcEqType is a proper implements the same Note [Non-trivial definitional -- equality] (in GHC.Core.TyCo.Rep) as `eqType`, but Type.eqType believes (* == -- Constraint), and that is NOT what we want in the type checker! tcEqType ty1 ty2 = tc_eq_type False False ki1 ki2 && tc_eq_type False False ty1 ty2 where ki1 = tcTypeKind ty1 ki2 = tcTypeKind ty2 -- | Just like 'tcEqType', but will return True for types of different kinds -- as long as their non-coercion structure is identical. tcEqTypeNoKindCheck :: TcType -> TcType -> Bool tcEqTypeNoKindCheck ty1 ty2 = tc_eq_type False False ty1 ty2 -- | Like 'tcEqType', but returns True if the /visible/ part of the types -- are equal, even if they are really unequal (in the invisible bits) tcEqTypeVis :: TcType -> TcType -> Bool tcEqTypeVis ty1 ty2 = tc_eq_type False True ty1 ty2 -- | Like 'pickyEqTypeVis', but returns a Bool for convenience pickyEqType :: TcType -> TcType -> Bool -- Check when two types _look_ the same, _including_ synonyms. -- So (pickyEqType String [Char]) returns False -- This ignores kinds and coercions, because this is used only for printing. pickyEqType ty1 ty2 = tc_eq_type True False ty1 ty2 -- | Real worker for 'tcEqType'. No kind check! tc_eq_type :: Bool -- ^ True <=> do not expand type synonyms -> Bool -- ^ True <=> compare visible args only -> Type -> Type -> Bool -- Flags False, False is the usual setting for tc_eq_type tc_eq_type keep_syns vis_only orig_ty1 orig_ty2 = go orig_env orig_ty1 orig_ty2 where go :: RnEnv2 -> Type -> Type -> Bool go env t1 t2 | not keep_syns, Just t1' <- tcView t1 = go env t1' t2 go env t1 t2 | not keep_syns, Just t2' <- tcView t2 = go env t1 t2' go env (TyVarTy tv1) (TyVarTy tv2) = rnOccL env tv1 == rnOccR env tv2 go _ (LitTy lit1) (LitTy lit2) = lit1 == lit2 go env (ForAllTy (Bndr tv1 vis1) ty1) (ForAllTy (Bndr tv2 vis2) ty2) = vis1 == vis2 && (vis_only || go env (varType tv1) (varType tv2)) && go (rnBndr2 env tv1 tv2) ty1 ty2 -- Make sure we handle all FunTy cases since falling through to the -- AppTy case means that tcRepSplitAppTy_maybe may see an unzonked -- kind variable, which causes things to blow up. go env (FunTy _ w1 arg1 res1) (FunTy _ w2 arg2 res2) = go env w1 w2 && go env arg1 arg2 && go env res1 res2 go env ty (FunTy _ w arg res) = eqFunTy env w arg res ty go env (FunTy _ w arg res) ty = eqFunTy env w arg res ty -- See Note [Equality on AppTys] in GHC.Core.Type go env (AppTy s1 t1) ty2 | Just (s2, t2) <- tcRepSplitAppTy_maybe ty2 = go env s1 s2 && go env t1 t2 go env ty1 (AppTy s2 t2) | Just (s1, t1) <- tcRepSplitAppTy_maybe ty1 = go env s1 s2 && go env t1 t2 go env (TyConApp tc1 ts1) (TyConApp tc2 ts2) = tc1 == tc2 && gos env (tc_vis tc1) ts1 ts2 go env (CastTy t1 _) t2 = go env t1 t2 go env t1 (CastTy t2 _) = go env t1 t2 go _ (CoercionTy {}) (CoercionTy {}) = True go _ _ _ = False gos _ _ [] [] = True gos env (ig:igs) (t1:ts1) (t2:ts2) = (ig || go env t1 t2) && gos env igs ts1 ts2 gos _ _ _ _ = False tc_vis :: TyCon -> [Bool] -- True for the fields we should ignore tc_vis tc | vis_only = inviss ++ repeat False -- Ignore invisibles | otherwise = repeat False -- Ignore nothing -- The repeat False is necessary because tycons -- can legitimately be oversaturated where bndrs = tyConBinders tc inviss = map isInvisibleTyConBinder bndrs orig_env = mkRnEnv2 $ mkInScopeSet $ tyCoVarsOfTypes [orig_ty1, orig_ty2] -- @eqFunTy w arg res ty@ is True when @ty@ equals @FunTy w arg res@. This is -- sometimes hard to know directly because @ty@ might have some casts -- obscuring the FunTy. And 'splitAppTy' is difficult because we can't -- always extract a RuntimeRep (see Note [xyz]) if the kind of the arg or -- res is unzonked/unflattened. Thus this function, which handles this -- corner case. eqFunTy :: RnEnv2 -> Mult -> Type -> Type -> Type -> Bool -- Last arg is /not/ FunTy eqFunTy env w arg res ty@(AppTy{}) = get_args ty [] where get_args :: Type -> [Type] -> Bool get_args (AppTy f x) args = get_args f (x:args) get_args (CastTy t _) args = get_args t args get_args (TyConApp tc tys) args | tc == funTyCon , [w', _, _, arg', res'] <- tys ++ args = go env w w' && go env arg arg' && go env res res' get_args _ _ = False eqFunTy _ _ _ _ _ = False {- ********************************************************************* * * Predicate types * * ************************************************************************ Deconstructors and tests on predicate types Note [Kind polymorphic type classes] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ class C f where... -- C :: forall k. k -> Constraint g :: forall (f::*). C f => f -> f Here the (C f) in the signature is really (C * f), and we don't want to complain that the * isn't a type variable! -} isTyVarClassPred :: PredType -> Bool isTyVarClassPred ty = case getClassPredTys_maybe ty of Just (_, tys) -> all isTyVarTy tys _ -> False ------------------------- checkValidClsArgs :: Bool -> Class -> [KindOrType] -> Bool -- If the Bool is True (flexible contexts), return True (i.e. ok) -- Otherwise, check that the type (not kind) args are all headed by a tyvar -- E.g. (Eq a) accepted, (Eq (f a)) accepted, but (Eq Int) rejected -- This function is here rather than in GHC.Tc.Validity because it is -- called from GHC.Tc.Solver, which itself is imported by GHC.Tc.Validity checkValidClsArgs flexible_contexts cls kts | flexible_contexts = True | otherwise = all hasTyVarHead tys where tys = filterOutInvisibleTypes (classTyCon cls) kts hasTyVarHead :: Type -> Bool -- Returns true of (a t1 .. tn), where 'a' is a type variable hasTyVarHead ty -- Haskell 98 allows predicates of form | tcIsTyVarTy ty = True -- C (a ty1 .. tyn) | otherwise -- where a is a type variable = case tcSplitAppTy_maybe ty of Just (ty, _) -> hasTyVarHead ty Nothing -> False evVarPred :: EvVar -> PredType evVarPred var = varType var -- Historical note: I used to have an ASSERT here, -- checking (isEvVarType (varType var)). But with something like -- f :: c => _ -> _ -- we end up with (c :: kappa), and (kappa ~ Constraint). Until -- we solve and zonk (which there is no particular reason to do for -- partial signatures, (isEvVarType kappa) will return False. But -- nothing is wrong. So I just removed the ASSERT. ------------------ -- | When inferring types, should we quantify over a given predicate? -- Generally true of classes; generally false of equality constraints. -- Equality constraints that mention quantified type variables and -- implicit variables complicate the story. See Notes -- [Inheriting implicit parameters] and [Quantifying over equality constraints] pickQuantifiablePreds :: TyVarSet -- Quantifying over these -> TcThetaType -- Proposed constraints to quantify -> TcThetaType -- A subset that we can actually quantify -- This function decides whether a particular constraint should be -- quantified over, given the type variables that are being quantified pickQuantifiablePreds qtvs theta = let flex_ctxt = True in -- Quantify over non-tyvar constraints, even without -- -XFlexibleContexts: see #10608, #10351 -- flex_ctxt <- xoptM Opt_FlexibleContexts mapMaybe (pick_me flex_ctxt) theta where pick_me flex_ctxt pred = case classifyPredType pred of ClassPred cls tys | Just {} <- isCallStackPred cls tys -- NEVER infer a CallStack constraint. Otherwise we let -- the constraints bubble up to be solved from the outer -- context, or be defaulted when we reach the top-level. -- See Note [Overview of implicit CallStacks] -> Nothing | isIPClass cls -> Just pred -- See note [Inheriting implicit parameters] | pick_cls_pred flex_ctxt cls tys -> Just pred EqPred eq_rel ty1 ty2 | quantify_equality eq_rel ty1 ty2 , Just (cls, tys) <- boxEqPred eq_rel ty1 ty2 -- boxEqPred: See Note [Lift equality constraints when quantifying] , pick_cls_pred flex_ctxt cls tys -> Just (mkClassPred cls tys) IrredPred ty | tyCoVarsOfType ty `intersectsVarSet` qtvs -> Just pred _ -> Nothing pick_cls_pred flex_ctxt cls tys = tyCoVarsOfTypes tys `intersectsVarSet` qtvs && (checkValidClsArgs flex_ctxt cls tys) -- Only quantify over predicates that checkValidType -- will pass! See #10351. -- See Note [Quantifying over equality constraints] quantify_equality NomEq ty1 ty2 = quant_fun ty1 || quant_fun ty2 quantify_equality ReprEq _ _ = True quant_fun ty = case tcSplitTyConApp_maybe ty of Just (tc, tys) | isTypeFamilyTyCon tc -> tyCoVarsOfTypes tys `intersectsVarSet` qtvs _ -> False boxEqPred :: EqRel -> Type -> Type -> Maybe (Class, [Type]) -- Given (t1 ~# t2) or (t1 ~R# t2) return the boxed version -- (t1 ~ t2) or (t1 `Coercible` t2) boxEqPred eq_rel ty1 ty2 = case eq_rel of NomEq | homo_kind -> Just (eqClass, [k1, ty1, ty2]) | otherwise -> Just (heqClass, [k1, k2, ty1, ty2]) ReprEq | homo_kind -> Just (coercibleClass, [k1, ty1, ty2]) | otherwise -> Nothing -- Sigh: we do not have hererogeneous Coercible -- so we can't abstract over it -- Nothing fundamental: we could add it where k1 = tcTypeKind ty1 k2 = tcTypeKind ty2 homo_kind = k1 `tcEqType` k2 pickCapturedPreds :: TyVarSet -- Quantifying over these -> TcThetaType -- Proposed constraints to quantify -> TcThetaType -- A subset that we can actually quantify -- A simpler version of pickQuantifiablePreds, used to winnow down -- the inferred constraints of a group of bindings, into those for -- one particular identifier pickCapturedPreds qtvs theta = filter captured theta where captured pred = isIPPred pred || (tyCoVarsOfType pred `intersectsVarSet` qtvs) -- Superclasses type PredWithSCs a = (PredType, [PredType], a) mkMinimalBySCs :: forall a. (a -> PredType) -> [a] -> [a] -- Remove predicates that -- -- - are the same as another predicate -- -- - can be deduced from another by superclasses, -- -- - are a reflexive equality (e.g * ~ *) -- (see Note [Remove redundant provided dicts] in GHC.Tc.TyCl.PatSyn) -- -- The result is a subset of the input. -- The 'a' is just paired up with the PredType; -- typically it might be a dictionary Id mkMinimalBySCs get_pred xs = go preds_with_scs [] where preds_with_scs :: [PredWithSCs a] preds_with_scs = [ (pred, pred : transSuperClasses pred, x) | x <- xs , let pred = get_pred x ] go :: [PredWithSCs a] -- Work list -> [PredWithSCs a] -- Accumulating result -> [a] go [] min_preds = reverse (map thdOf3 min_preds) -- The 'reverse' isn't strictly necessary, but it -- means that the results are returned in the same -- order as the input, which is generally saner go (work_item@(p,_,_) : work_list) min_preds | EqPred _ t1 t2 <- classifyPredType p , t1 `tcEqType` t2 -- See GHC.Tc.TyCl.PatSyn -- Note [Remove redundant provided dicts] = go work_list min_preds | p `in_cloud` work_list || p `in_cloud` min_preds = go work_list min_preds | otherwise = go work_list (work_item : min_preds) in_cloud :: PredType -> [PredWithSCs a] -> Bool in_cloud p ps = or [ p `tcEqType` p' | (_, scs, _) <- ps, p' <- scs ] transSuperClasses :: PredType -> [PredType] -- (transSuperClasses p) returns (p's superclasses) not including p -- Stop if you encounter the same class again -- See Note [Expanding superclasses] transSuperClasses p = go emptyNameSet p where go :: NameSet -> PredType -> [PredType] go rec_clss p | ClassPred cls tys <- classifyPredType p , let cls_nm = className cls , not (cls_nm `elemNameSet` rec_clss) , let rec_clss' | isCTupleClass cls = rec_clss | otherwise = rec_clss `extendNameSet` cls_nm = [ p' | sc <- immSuperClasses cls tys , p' <- sc : go rec_clss' sc ] | otherwise = [] immSuperClasses :: Class -> [Type] -> [PredType] immSuperClasses cls tys = substTheta (zipTvSubst tyvars tys) sc_theta where (tyvars,sc_theta,_,_) = classBigSig cls isImprovementPred :: PredType -> Bool -- Either it's an equality, or has some functional dependency isImprovementPred ty = case classifyPredType ty of EqPred NomEq t1 t2 -> not (t1 `tcEqType` t2) EqPred ReprEq _ _ -> False ClassPred cls _ -> classHasFds cls IrredPred {} -> True -- Might have equalities after reduction? ForAllPred {} -> False -- | Is the equality -- a ~r ...a.... -- definitely insoluble or not? -- a ~r Maybe a -- Definitely insoluble -- a ~N ...(F a)... -- Not definitely insoluble -- -- Perhaps (F a) reduces to Int -- a ~R ...(N a)... -- Not definitely insoluble -- -- Perhaps newtype N a = MkN Int -- See Note [Occurs check error] in -- "GHC.Tc.Solver.Canonical" for the motivation for this function. isInsolubleOccursCheck :: EqRel -> TcTyVar -> TcType -> Bool isInsolubleOccursCheck eq_rel tv ty = go ty where go ty | Just ty' <- tcView ty = go ty' go (TyVarTy tv') = tv == tv' || go (tyVarKind tv') go (LitTy {}) = False go (AppTy t1 t2) = case eq_rel of -- See Note [AppTy and ReprEq] NomEq -> go t1 || go t2 ReprEq -> go t1 go (FunTy _ w t1 t2) = go w || go t1 || go t2 go (ForAllTy (Bndr tv' _) inner_ty) | tv' == tv = False | otherwise = go (varType tv') || go inner_ty go (CastTy ty _) = go ty -- ToDo: what about the coercion go (CoercionTy _) = False -- ToDo: what about the coercion go (TyConApp tc tys) | isGenerativeTyCon tc role = any go tys | otherwise = any go (drop (tyConArity tc) tys) -- (a ~ F b a), where F has arity 1, -- has an insoluble occurs check role = eqRelRole eq_rel {- Note [Expanding superclasses] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ When we expand superclasses, we use the following algorithm: transSuperClasses( C tys ) returns the transitive superclasses of (C tys), not including C itself For example class C a b => D a b class D b a => C a b Then transSuperClasses( Ord ty ) = [Eq ty] transSuperClasses( C ta tb ) = [D tb ta, C tb ta] Notice that in the recursive-superclass case we include C again at the end of the chain. One could exclude C in this case, but the code is more awkward and there seems no good reason to do so. (However C.f. GHC.Tc.Solver.Canonical.mk_strict_superclasses, which /does/ appear to do so.) The algorithm is expand( so_far, pred ): 1. If pred is not a class constraint, return empty set Otherwise pred = C ts 2. If C is in so_far, return empty set (breaks loops) 3. Find the immediate superclasses constraints of (C ts) 4. For each such sc_pred, return (sc_pred : expand( so_far+C, D ss ) Notice that * With normal Haskell-98 classes, the loop-detector will never bite, so we'll get all the superclasses. * We need the loop-breaker in case we have UndecidableSuperClasses on * Since there is only a finite number of distinct classes, expansion must terminate. * The loop breaking is a bit conservative. Notably, a tuple class could contain many times without threatening termination: (Eq a, (Ord a, Ix a)) And this is try of any class that we can statically guarantee as non-recursive (in some sense). For now, we just make a special case for tuples. Something better would be cool. See also GHC.Tc.TyCl.Utils.checkClassCycles. Note [Lift equality constraints when quantifying] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ We can't quantify over a constraint (t1 ~# t2) because that isn't a predicate type; see Note [Types for coercions, predicates, and evidence] in GHC.Core.TyCo.Rep. So we have to 'lift' it to (t1 ~ t2). Similarly (~R#) must be lifted to Coercible. This tiresome lifting is the reason that pick_me (in pickQuantifiablePreds) returns a Maybe rather than a Bool. Note [Quantifying over equality constraints] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Should we quantify over an equality constraint (s ~ t)? In general, we don't. Doing so may simply postpone a type error from the function definition site to its call site. (At worst, imagine (Int ~ Bool)). However, consider this forall a. (F [a] ~ Int) => blah Should we quantify over the (F [a] ~ Int)? Perhaps yes, because at the call site we will know 'a', and perhaps we have instance F [Bool] = Int. So we *do* quantify over a type-family equality where the arguments mention the quantified variables. Note [Inheriting implicit parameters] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Consider this: f x = (x::Int) + ?y where f is *not* a top-level binding. From the RHS of f we'll get the constraint (?y::Int). There are two types we might infer for f: f :: Int -> Int (so we get ?y from the context of f's definition), or f :: (?y::Int) => Int -> Int At first you might think the first was better, because then ?y behaves like a free variable of the definition, rather than having to be passed at each call site. But of course, the WHOLE IDEA is that ?y should be passed at each call site (that's what dynamic binding means) so we'd better infer the second. BOTTOM LINE: when *inferring types* you must quantify over implicit parameters, *even if* they don't mention the bound type variables. Reason: because implicit parameters, uniquely, have local instance declarations. See pickQuantifiablePreds. Note [Quantifying over equality constraints] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Should we quantify over an equality constraint (s ~ t)? In general, we don't. Doing so may simply postpone a type error from the function definition site to its call site. (At worst, imagine (Int ~ Bool)). However, consider this forall a. (F [a] ~ Int) => blah Should we quantify over the (F [a] ~ Int). Perhaps yes, because at the call site we will know 'a', and perhaps we have instance F [Bool] = Int. So we *do* quantify over a type-family equality where the arguments mention the quantified variables. ************************************************************************ * * Classifying types * * ************************************************************************ -} isSigmaTy :: TcType -> Bool -- isSigmaTy returns true of any qualified type. It doesn't -- *necessarily* have any foralls. E.g -- f :: (?x::Int) => Int -> Int isSigmaTy ty | Just ty' <- tcView ty = isSigmaTy ty' isSigmaTy (ForAllTy {}) = True isSigmaTy (FunTy { ft_af = InvisArg }) = True isSigmaTy _ = False isRhoTy :: TcType -> Bool -- True of TcRhoTypes; see Note [TcRhoType] isRhoTy ty | Just ty' <- tcView ty = isRhoTy ty' isRhoTy (ForAllTy {}) = False isRhoTy (FunTy { ft_af = InvisArg }) = False isRhoTy _ = True -- | Like 'isRhoTy', but also says 'True' for 'Infer' types isRhoExpTy :: ExpType -> Bool isRhoExpTy (Check ty) = isRhoTy ty isRhoExpTy (Infer {}) = True isOverloadedTy :: Type -> Bool -- Yes for a type of a function that might require evidence-passing -- Used only by bindLocalMethods isOverloadedTy ty | Just ty' <- tcView ty = isOverloadedTy ty' isOverloadedTy (ForAllTy _ ty) = isOverloadedTy ty isOverloadedTy (FunTy { ft_af = InvisArg }) = True isOverloadedTy _ = False isFloatTy, isDoubleTy, isIntegerTy, isNaturalTy, isIntTy, isWordTy, isBoolTy, isUnitTy, isCharTy, isAnyTy :: Type -> Bool isFloatTy = is_tc floatTyConKey isDoubleTy = is_tc doubleTyConKey isIntegerTy = is_tc integerTyConKey isNaturalTy = is_tc naturalTyConKey isIntTy = is_tc intTyConKey isWordTy = is_tc wordTyConKey isBoolTy = is_tc boolTyConKey isUnitTy = is_tc unitTyConKey isCharTy = is_tc charTyConKey isAnyTy = is_tc anyTyConKey -- | Does a type represent a floating-point number? isFloatingTy :: Type -> Bool isFloatingTy ty = isFloatTy ty || isDoubleTy ty -- | Is a type 'String'? isStringTy :: Type -> Bool isStringTy ty = case tcSplitTyConApp_maybe ty of Just (tc, [arg_ty]) -> tc == listTyCon && isCharTy arg_ty _ -> False -- | Is a type a 'CallStack'? isCallStackTy :: Type -> Bool isCallStackTy ty | Just tc <- tyConAppTyCon_maybe ty = tc `hasKey` callStackTyConKey | otherwise = False -- | Is a 'PredType' a 'CallStack' implicit parameter? -- -- If so, return the name of the parameter. isCallStackPred :: Class -> [Type] -> Maybe FastString isCallStackPred cls tys | [ty1, ty2] <- tys , isIPClass cls , isCallStackTy ty2 = isStrLitTy ty1 | otherwise = Nothing is_tc :: Unique -> Type -> Bool -- Newtypes are opaque to this is_tc uniq ty = case tcSplitTyConApp_maybe ty of Just (tc, _) -> uniq == getUnique tc Nothing -> False -- | Does the given tyvar appear at the head of a chain of applications -- (a t1 ... tn) isTyVarHead :: TcTyVar -> TcType -> Bool isTyVarHead tv (TyVarTy tv') = tv == tv' isTyVarHead tv (AppTy fun _) = isTyVarHead tv fun isTyVarHead tv (CastTy ty _) = isTyVarHead tv ty isTyVarHead _ (TyConApp {}) = False isTyVarHead _ (LitTy {}) = False isTyVarHead _ (ForAllTy {}) = False isTyVarHead _ (FunTy {}) = False isTyVarHead _ (CoercionTy {}) = False {- Note [AppTy and ReprEq] ~~~~~~~~~~~~~~~~~~~~~~~~~~ Consider a ~R# b a a ~R# a b The former is /not/ a definite error; we might instantiate 'b' with Id newtype Id a = MkId a but the latter /is/ a definite error. On the other hand, with nominal equality, both are definite errors -} isRigidTy :: TcType -> Bool isRigidTy ty | Just (tc,_) <- tcSplitTyConApp_maybe ty = isGenerativeTyCon tc Nominal | Just {} <- tcSplitAppTy_maybe ty = True | isForAllTy ty = True | otherwise = False -- | Is this type *almost function-free*? See Note [Almost function-free] -- in "GHC.Tc.Types" isAlmostFunctionFree :: TcType -> Bool isAlmostFunctionFree ty | Just ty' <- tcView ty = isAlmostFunctionFree ty' isAlmostFunctionFree (TyVarTy {}) = True isAlmostFunctionFree (AppTy ty1 ty2) = isAlmostFunctionFree ty1 && isAlmostFunctionFree ty2 isAlmostFunctionFree (TyConApp tc args) | isTypeFamilyTyCon tc = False | otherwise = all isAlmostFunctionFree args isAlmostFunctionFree (ForAllTy bndr _) = isAlmostFunctionFree (binderType bndr) isAlmostFunctionFree (FunTy _ w ty1 ty2) = isAlmostFunctionFree w && isAlmostFunctionFree ty1 && isAlmostFunctionFree ty2 isAlmostFunctionFree (LitTy {}) = True isAlmostFunctionFree (CastTy ty _) = isAlmostFunctionFree ty isAlmostFunctionFree (CoercionTy {}) = True {- ************************************************************************ * * Misc * * ************************************************************************ Note [Visible type application] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ GHC implements a generalisation of the algorithm described in the "Visible Type Application" paper (available from http://www.cis.upenn.edu/~sweirich/publications.html). A key part of that algorithm is to distinguish user-specified variables from inferred variables. For example, the following should typecheck: f :: forall a b. a -> b -> b f = const id g = const id x = f @Int @Bool 5 False y = g 5 @Bool False The idea is that we wish to allow visible type application when we are instantiating a specified, fixed variable. In practice, specified, fixed variables are either written in a type signature (or annotation), OR are imported from another module. (We could do better here, for example by doing SCC analysis on parts of a module and considering any type from outside one's SCC to be fully specified, but this is very confusing to users. The simple rule above is much more straightforward and predictable.) So, both of f's quantified variables are specified and may be instantiated. But g has no type signature, so only id's variable is specified (because id is imported). We write the type of g as forall {a}. a -> forall b. b -> b. Note that the a is in braces, meaning it cannot be instantiated with visible type application. Tracking specified vs. inferred variables is done conveniently by a field in TyBinder. -} deNoteType :: Type -> Type -- Remove all *outermost* type synonyms and other notes deNoteType ty | Just ty' <- coreView ty = deNoteType ty' deNoteType ty = ty {- Find the free tycons and classes of a type. This is used in the front end of the compiler. -} {- ************************************************************************ * * External types * * ************************************************************************ The compiler's foreign function interface supports the passing of a restricted set of types as arguments and results (the restricting factor being the ) -} tcSplitIOType_maybe :: Type -> Maybe (TyCon, Type) -- (tcSplitIOType_maybe t) returns Just (IO,t',co) -- if co : t ~ IO t' -- returns Nothing otherwise tcSplitIOType_maybe ty = case tcSplitTyConApp_maybe ty of Just (io_tycon, [io_res_ty]) | io_tycon `hasKey` ioTyConKey -> Just (io_tycon, io_res_ty) _ -> Nothing isFFITy :: Type -> Bool -- True for any TyCon that can possibly be an arg or result of an FFI call isFFITy ty = isValid (checkRepTyCon legalFFITyCon ty) isFFIArgumentTy :: DynFlags -> Safety -> Type -> Validity -- Checks for valid argument type for a 'foreign import' isFFIArgumentTy dflags safety ty = checkRepTyCon (legalOutgoingTyCon dflags safety) ty isFFIExternalTy :: Type -> Validity -- Types that are allowed as arguments of a 'foreign export' isFFIExternalTy ty = checkRepTyCon legalFEArgTyCon ty isFFIImportResultTy :: DynFlags -> Type -> Validity isFFIImportResultTy dflags ty = checkRepTyCon (legalFIResultTyCon dflags) ty isFFIExportResultTy :: Type -> Validity isFFIExportResultTy ty = checkRepTyCon legalFEResultTyCon ty isFFIDynTy :: Type -> Type -> Validity -- The type in a foreign import dynamic must be Ptr, FunPtr, or a newtype of -- either, and the wrapped function type must be equal to the given type. -- We assume that all types have been run through normaliseFfiType, so we don't -- need to worry about expanding newtypes here. isFFIDynTy expected ty -- Note [Foreign import dynamic] -- In the example below, expected would be 'CInt -> IO ()', while ty would -- be 'FunPtr (CDouble -> IO ())'. | Just (tc, [ty']) <- splitTyConApp_maybe ty , tyConUnique tc `elem` [ptrTyConKey, funPtrTyConKey] , eqType ty' expected = IsValid | otherwise = NotValid (vcat [ text "Expected: Ptr/FunPtr" <+> pprParendType expected <> comma , text " Actual:" <+> ppr ty ]) isFFILabelTy :: Type -> Validity -- The type of a foreign label must be Ptr, FunPtr, or a newtype of either. isFFILabelTy ty = checkRepTyCon ok ty where ok tc | tc `hasKey` funPtrTyConKey || tc `hasKey` ptrTyConKey = IsValid | otherwise = NotValid (text "A foreign-imported address (via &foo) must have type (Ptr a) or (FunPtr a)") isFFIPrimArgumentTy :: DynFlags -> Type -> Validity -- Checks for valid argument type for a 'foreign import prim' -- Currently they must all be simple unlifted types, or the well-known type -- Any, which can be used to pass the address to a Haskell object on the heap to -- the foreign function. isFFIPrimArgumentTy dflags ty | isAnyTy ty = IsValid | otherwise = checkRepTyCon (legalFIPrimArgTyCon dflags) ty isFFIPrimResultTy :: DynFlags -> Type -> Validity -- Checks for valid result type for a 'foreign import prim' Currently -- it must be an unlifted type, including unboxed tuples, unboxed -- sums, or the well-known type Any. isFFIPrimResultTy dflags ty | isAnyTy ty = IsValid | otherwise = checkRepTyCon (legalFIPrimResultTyCon dflags) ty isFunPtrTy :: Type -> Bool isFunPtrTy ty | Just (tc, [_]) <- splitTyConApp_maybe ty = tc `hasKey` funPtrTyConKey | otherwise = False -- normaliseFfiType gets run before checkRepTyCon, so we don't -- need to worry about looking through newtypes or type functions -- here; that's already been taken care of. checkRepTyCon :: (TyCon -> Validity) -> Type -> Validity checkRepTyCon check_tc ty = case splitTyConApp_maybe ty of Just (tc, tys) | isNewTyCon tc -> NotValid (hang msg 2 (mk_nt_reason tc tys $$ nt_fix)) | otherwise -> case check_tc tc of IsValid -> IsValid NotValid extra -> NotValid (msg $$ extra) Nothing -> NotValid (quotes (ppr ty) <+> text "is not a data type") where msg = quotes (ppr ty) <+> text "cannot be marshalled in a foreign call" mk_nt_reason tc tys | null tys = text "because its data constructor is not in scope" | otherwise = text "because the data constructor for" <+> quotes (ppr tc) <+> text "is not in scope" nt_fix = text "Possible fix: import the data constructor to bring it into scope" {- Note [Foreign import dynamic] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ A dynamic stub must be of the form 'FunPtr ft -> ft' where ft is any foreign type. Similarly, a wrapper stub must be of the form 'ft -> IO (FunPtr ft)'. We use isFFIDynTy to check whether a signature is well-formed. For example, given a (illegal) declaration like: foreign import ccall "dynamic" foo :: FunPtr (CDouble -> IO ()) -> CInt -> IO () isFFIDynTy will compare the 'FunPtr' type 'CDouble -> IO ()' with the curried result type 'CInt -> IO ()', and return False, as they are not equal. ---------------------------------------------- These chaps do the work; they are not exported ---------------------------------------------- -} legalFEArgTyCon :: TyCon -> Validity legalFEArgTyCon tc -- It's illegal to make foreign exports that take unboxed -- arguments. The RTS API currently can't invoke such things. --SDM 7/2000 = boxedMarshalableTyCon tc legalFIResultTyCon :: DynFlags -> TyCon -> Validity legalFIResultTyCon dflags tc | tc == unitTyCon = IsValid | otherwise = marshalableTyCon dflags tc legalFEResultTyCon :: TyCon -> Validity legalFEResultTyCon tc | tc == unitTyCon = IsValid | otherwise = boxedMarshalableTyCon tc legalOutgoingTyCon :: DynFlags -> Safety -> TyCon -> Validity -- Checks validity of types going from Haskell -> external world legalOutgoingTyCon dflags _ tc = marshalableTyCon dflags tc legalFFITyCon :: TyCon -> Validity -- True for any TyCon that can possibly be an arg or result of an FFI call legalFFITyCon tc | isUnliftedTyCon tc = IsValid | tc == unitTyCon = IsValid | otherwise = boxedMarshalableTyCon tc marshalableTyCon :: DynFlags -> TyCon -> Validity marshalableTyCon dflags tc | isUnliftedTyCon tc , not (isUnboxedTupleTyCon tc || isUnboxedSumTyCon tc) , not (null (tyConPrimRep tc)) -- Note [Marshalling void] = validIfUnliftedFFITypes dflags | otherwise = boxedMarshalableTyCon tc boxedMarshalableTyCon :: TyCon -> Validity boxedMarshalableTyCon tc | getUnique tc `elem` [ intTyConKey, int8TyConKey, int16TyConKey , int32TyConKey, int64TyConKey , wordTyConKey, word8TyConKey, word16TyConKey , word32TyConKey, word64TyConKey , floatTyConKey, doubleTyConKey , ptrTyConKey, funPtrTyConKey , charTyConKey , stablePtrTyConKey , boolTyConKey ] = IsValid | otherwise = NotValid empty legalFIPrimArgTyCon :: DynFlags -> TyCon -> Validity -- Check args of 'foreign import prim', only allow simple unlifted types. -- Strictly speaking it is unnecessary to ban unboxed tuples and sums here since -- currently they're of the wrong kind to use in function args anyway. legalFIPrimArgTyCon dflags tc | isUnliftedTyCon tc , not (isUnboxedTupleTyCon tc || isUnboxedSumTyCon tc) = validIfUnliftedFFITypes dflags | otherwise = NotValid unlifted_only legalFIPrimResultTyCon :: DynFlags -> TyCon -> Validity -- Check result type of 'foreign import prim'. Allow simple unlifted -- types and also unboxed tuple and sum result types. legalFIPrimResultTyCon dflags tc | isUnliftedTyCon tc , isUnboxedTupleTyCon tc || isUnboxedSumTyCon tc || not (null (tyConPrimRep tc)) -- Note [Marshalling void] = validIfUnliftedFFITypes dflags | otherwise = NotValid unlifted_only unlifted_only :: MsgDoc unlifted_only = text "foreign import prim only accepts simple unlifted types" validIfUnliftedFFITypes :: DynFlags -> Validity validIfUnliftedFFITypes dflags | xopt LangExt.UnliftedFFITypes dflags = IsValid | otherwise = NotValid (text "To marshal unlifted types, use UnliftedFFITypes") {- Note [Marshalling void] ~~~~~~~~~~~~~~~~~~~~~~~ We don't treat State# (whose PrimRep is VoidRep) as marshalable. In turn that means you can't write foreign import foo :: Int -> State# RealWorld Reason: the back end falls over with panic "primRepHint:VoidRep"; and there is no compelling reason to permit it -} {- ************************************************************************ * * The "Paterson size" of a type * * ************************************************************************ -} {- Note [Paterson conditions on PredTypes] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ We are considering whether *class* constraints terminate (see Note [Paterson conditions]). Precisely, the Paterson conditions would have us check that "the constraint has fewer constructors and variables (taken together and counting repetitions) than the head.". However, we can be a bit more refined by looking at which kind of constraint this actually is. There are two main tricks: 1. It seems like it should be OK not to count the tuple type constructor for a PredType like (Show a, Eq a) :: Constraint, since we don't count the "implicit" tuple in the ThetaType itself. In fact, the Paterson test just checks *each component* of the top level ThetaType against the size bound, one at a time. By analogy, it should be OK to return the size of the *largest* tuple component as the size of the whole tuple. 2. Once we get into an implicit parameter or equality we can't get back to a class constraint, so it's safe to say "size 0". See #4200. NB: we don't want to detect PredTypes in sizeType (and then call sizePred on them), or we might get an infinite loop if that PredType is irreducible. See #5581. -} type TypeSize = IntWithInf sizeType :: Type -> TypeSize -- Size of a type: the number of variables and constructors -- Ignore kinds altogether sizeType = go where go ty | Just exp_ty <- tcView ty = go exp_ty go (TyVarTy {}) = 1 go (TyConApp tc tys) | isTypeFamilyTyCon tc = infinity -- Type-family applications can -- expand to any arbitrary size | otherwise = sizeTypes (filterOutInvisibleTypes tc tys) + 1 -- Why filter out invisible args? I suppose any -- size ordering is sound, but why is this better? -- I came across this when investigating #14010. go (LitTy {}) = 1 go (FunTy _ w arg res) = go w + go arg + go res + 1 go (AppTy fun arg) = go fun + go arg go (ForAllTy (Bndr tv vis) ty) | isVisibleArgFlag vis = go (tyVarKind tv) + go ty + 1 | otherwise = go ty + 1 go (CastTy ty _) = go ty go (CoercionTy {}) = 0 sizeTypes :: [Type] -> TypeSize sizeTypes tys = sum (map sizeType tys) ----------------------------------------------------------------------------------- ----------------------------------------------------------------------------------- ----------------------- -- | For every arg a tycon can take, the returned list says True if the argument -- is taken visibly, and False otherwise. Ends with an infinite tail of Trues to -- allow for oversaturation. tcTyConVisibilities :: TyCon -> [Bool] tcTyConVisibilities tc = tc_binder_viss ++ tc_return_kind_viss ++ repeat True where tc_binder_viss = map isVisibleTyConBinder (tyConBinders tc) tc_return_kind_viss = map isVisibleBinder (fst $ tcSplitPiTys (tyConResKind tc)) -- | If the tycon is applied to the types, is the next argument visible? isNextTyConArgVisible :: TyCon -> [Type] -> Bool isNextTyConArgVisible tc tys = tcTyConVisibilities tc `getNth` length tys -- | Should this type be applied to a visible argument? isNextArgVisible :: TcType -> Bool isNextArgVisible ty | Just (bndr, _) <- tcSplitPiTy_maybe ty = isVisibleBinder bndr | otherwise = True -- this second case might happen if, say, we have an unzonked TauTv. -- But TauTvs can't range over types that take invisible arguments