{-# LANGUAGE FlexibleContexts #-} {-# LANGUAGE ScopedTypeVariables #-} {-# LANGUAGE TupleSections #-} {-# OPTIONS_GHC -Wno-incomplete-record-updates #-} {- (c) The University of Glasgow 2006 (c) The GRASP/AQUA Project, Glasgow University, 1992-1998 -} -- | 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, TcTypeFRR, TcSigmaTypeFRR, TcRhoType, TcTauType, TcPredType, TcThetaType, TcTyVar, TcTyVarSet, TcDTyVarSet, TcTyCoVarSet, TcDTyCoVarSet, TcKind, TcCoVar, TcTyCoVar, TcTyVarBinder, TcInvisTVBinder, TcReqTVBinder, TcTyCon, MonoTcTyCon, PolyTcTyCon, TcTyConBinder, KnotTied, ExpType(..), InferResult(..), ExpTypeFRR, ExpSigmaType, ExpSigmaTypeFRR, ExpRhoType, mkCheckExpType, SyntaxOpType(..), synKnownType, mkSynFunTys, -- TcLevel TcLevel(..), topTcLevel, pushTcLevel, isTopTcLevel, strictlyDeeperThan, deeperThanOrSame, sameDepthAs, tcTypeLevel, tcTyVarLevel, maxTcLevel, -------------------------------- -- MetaDetails TcTyVarDetails(..), pprTcTyVarDetails, vanillaSkolemTvUnk, MetaDetails(Flexi, Indirect), MetaInfo(..), skolemSkolInfo, isImmutableTyVar, isSkolemTyVar, isMetaTyVar, isMetaTyVarTy, isTyVarTy, tcIsTcTyVar, isTyVarTyVar, isOverlappableTyVar, isTyConableTyVar, ConcreteTvOrigin(..), isConcreteTyVar_maybe, isConcreteTyVar, isConcreteTyVarTy, isConcreteTyVarTy_maybe, isAmbiguousTyVar, isCycleBreakerTyVar, metaTyVarRef, metaTyVarInfo, isFlexi, isIndirect, isRuntimeUnkSkol, metaTyVarTcLevel, setMetaTyVarTcLevel, metaTyVarTcLevel_maybe, isTouchableMetaTyVar, isPromotableMetaTyVar, findDupTyVarTvs, mkTyVarNamePairs, -------------------------------- -- Builders mkPhiTy, mkInfSigmaTy, mkSpecSigmaTy, mkSigmaTy, mkTcAppTy, mkTcAppTys, mkTcCastTy, -------------------------------- -- Splitters -- These are important because they do not look through newtypes getTyVar, tcSplitForAllTyVarBinder_maybe, tcSplitForAllTyVars, tcSplitForAllInvisTyVars, tcSplitSomeForAllTyVars, tcSplitForAllReqTVBinders, tcSplitForAllInvisTVBinders, tcSplitPiTys, tcSplitPiTy_maybe, tcSplitForAllTyVarBinders, 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, tcEqTyConApps, isSigmaTy, isRhoTy, isRhoExpTy, isOverloadedTy, isFloatingPrimTy, isDoubleTy, isFloatTy, isIntTy, isWordTy, isStringTy, isIntegerTy, isNaturalTy, isBoolTy, isUnitTy, isCharTy, isTauTy, isTauTyCon, tcIsTyVarTy, tcIsForAllTy, isPredTy, isTyVarClassPred, checkValidClsArgs, hasTyVarHead, isRigidTy, --------------------------------- -- Misc type manipulators deNoteType, orphNamesOfType, orphNamesOfCo, orphNamesOfTypes, orphNamesOfCoCon, getDFunTyKey, evVarPred, ambigTkvsOfTy, --------------------------------- -- Predicate types mkMinimalBySCs, transSuperClasses, pickCapturedPreds, immSuperClasses, boxEqPred, isImprovementPred, -- * Finding type instances tcTyFamInsts, tcTyFamInstsAndVis, tcTyConAppTyFamInstsAndVis, isTyFamFree, -- * Finding "exact" (non-dead) type variables exactTyCoVarsOfType, exactTyCoVarsOfTypes, anyRewritableTyVar, anyRewritableTyFamApp, --------------------------------- -- Foreign import and export IllegalForeignTypeReason(..), TypeCannotBeMarshaledReason(..), 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 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, isIPLikePred, isEqPred, isEqPredClass, mkClassPred, tcSplitDFunTy, tcSplitDFunHead, tcSplitMethodTy, isRuntimeRepVar, isFixedRuntimeRepKind, 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, pprTheta, pprParendTheta, pprThetaArrowTy, pprClassPred, pprTCvBndr, pprTCvBndrs, TypeSize, sizeType, sizeTypes, scopedSort, --------------------------------- -- argument visibility tcTyConVisibilities, isNextTyConArgVisible, isNextArgVisible ) where -- 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 import {-# SOURCE #-} GHC.Tc.Types.Origin ( SkolemInfo, unkSkol , FixedRuntimeRepOrigin, FixedRuntimeRepContext ) -- 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.Utils.Panic import GHC.Utils.Panic.Plain import GHC.Utils.Error( Validity'(..) ) import qualified GHC.LanguageExtensions as LangExt import Data.IORef import Data.List.NonEmpty( NonEmpty(..) ) import Data.List ( partition ) {- ************************************************************************ * * 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 -- | A type which has a syntactically fixed RuntimeRep as per -- Note [Fixed RuntimeRep] in GHC.Tc.Utils.Concrete. type TcTypeFRR = TcType -- TODO: consider making this a newtype. type TcTyVarBinder = TyVarBinder type TcInvisTVBinder = InvisTVBinder type TcReqTVBinder = ReqTVBinder -- See Note [TcTyCon, MonoTcTyCon, and PolyTcTyCon] type TcTyCon = TyCon type MonoTcTyCon = TcTyCon type PolyTcTyCon = TcTyCon type TcTyConBinder = TyConBinder -- With skolem TcTyVars -- These types do not have boxy type variables in them type TcPredType = PredType type TcThetaType = ThetaType type TcSigmaType = TcType -- | A 'TcSigmaTypeFRR' is a 'TcSigmaType' which has a syntactically -- fixed 'RuntimeRep' in the sense of Note [Fixed RuntimeRep] -- in GHC.Tc.Utils.Concrete. -- -- In particular, this means that: -- -- - 'GHC.Types.RepType.typePrimRep' does not panic, -- - 'GHC.Core.typeLevity_maybe' does not return 'Nothing'. -- -- This property is important in functions such as 'matchExpectedFunTys', where -- we want to provide argument types which have a known runtime representation. -- See Note [Return arguments with a fixed RuntimeRep. type TcSigmaTypeFRR = TcSigmaType -- TODO: consider making this a newtype. type TcRhoType = TcType -- Note [TcRhoType] type TcTauType = TcType type TcKind = Kind type TcTyVarSet = TyVarSet type TcTyCoVarSet = TyCoVarSet type TcDTyVarSet = DTyVarSet type TcDTyCoVarSet = DTyCoVarSet {- Note [TcTyCon, MonoTcTyCon, and PolyTcTyCon] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ See Note [How TcTyCons work] in GHC.Tc.TyCl Invariants: * TcTyCon: a TyCon built with the TcTyCon constructor * TcTyConBinder: a TyConBinder with a TcTyVar inside (not a TyVar) * TcTyCons contain TcTyVars * MonoTcTyCon: - Flag tcTyConIsPoly = False - tyConScopedTyVars is important; maps a Name to a TyVarTv unification variable The order is important: Specified then Required variables. E.g. in data T a (b :: k) = ... the order will be [k, a, b]. NB: There are no Inferred binders in tyConScopedTyVars; 'a' may also be poly-kinded, but that kind variable will be added by generaliseTcTyCon, in the passage to a PolyTcTyCon. - tyConBinders are irrelevant; we just use tcTyConScopedTyVars Well not /quite/ irrelevant: its length gives the number of Required binders, and so allows up to distinguish between the Specified and Required elements of tyConScopedTyVars. * PolyTcTyCon: - Flag tcTyConIsPoly = True; this is used only to short-cut zonking - tyConBinders are still TcTyConBinders, but they are /skolem/ TcTyVars, with fixed kinds: no unification variables here tyConBinders includes the Inferred binders if any tyConBinders uses the Names from the original, renamed program. - tcTyConScopedTyVars is irrelevant: just use (binderVars tyConBinders) All the types have been swizzled back to use the original Names See Note [tyConBinders and lexical scoping] in GHC.Core.TyCon -} {- ********************************************************************* * * 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 -- ^ This 'Unique' is for debugging only , ir_lvl :: TcLevel -- ^ See Note [TcLevel of ExpType] in GHC.Tc.Utils.TcMType , ir_frr :: Maybe FixedRuntimeRepContext -- ^ See Note [FixedRuntimeRep context in 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 :: RuntimeRep@. -- -- Additionally, if the 'ir_frr' field is @Just frr_orig@ then -- @rr@ must be concrete, in the sense of Note [Concrete types] -- in GHC.Tc.Utils.Concrete. type ExpSigmaType = ExpType -- | An 'ExpType' which has a fixed RuntimeRep. -- -- For a 'Check' 'ExpType', the stored 'TcType' must have -- a fixed RuntimeRep. For an 'Infer' 'ExpType', the 'ir_frr' -- field must be of the form @Just frr_orig@. type ExpTypeFRR = ExpType -- | Like 'TcSigmaTypeFRR', but for an expected type. -- -- See 'ExpTypeFRR'. type ExpSigmaTypeFRR = ExpTypeFRR -- TODO: consider making this a newtype. 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, ir_frr = mb_frr }) = text "Infer" <> mb_frr_text <> braces (ppr u <> comma <> ppr lvl) where mb_frr_text = case mb_frr of Just _ -> text "FRR" Nothing -> empty -- | 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 [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 SkolemInfo 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 invariants] vanillaSkolemTvUnk :: HasCallStack => TcTyVarDetails vanillaSkolemTvUnk = SkolemTv unkSkol topTcLevel False instance Outputable TcTyVarDetails where ppr = pprTcTyVarDetails pprTcTyVarDetails :: TcTyVarDetails -> SDoc -- For debugging pprTcTyVarDetails (RuntimeUnk {}) = text "rt" pprTcTyVarDetails (SkolemTv _sk lvl True) = text "ssk" <> colon <> ppr lvl pprTcTyVarDetails (SkolemTv _sk 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 -- | What restrictions are on this metavariable around unification? -- These are checked in GHC.Tc.Utils.Unify.startSolvingByUnification. 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 [TyVarTv] in GHC.Tc.Utils.TcMType | RuntimeUnkTv -- ^ A unification variable used in the GHCi debugger. -- It /is/ allowed to unify with a polytype, unlike TauTv | CycleBreakerTv -- Used to fix occurs-check problems in Givens -- See Note [Type equality cycles] in -- GHC.Tc.Solver.Canonical | ConcreteTv ConcreteTvOrigin -- ^ A unification variable that can only be unified -- with a concrete type, in the sense of -- Note [Concrete types] in GHC.Tc.Utils.Concrete. -- See Note [ConcreteTv] in GHC.Tc.Utils.Concrete. -- See also Note [The Concrete mechanism] in GHC.Tc.Utils.Concrete -- for an overview of how this works in context. 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 RuntimeUnkTv = text "rutv" ppr CycleBreakerTv = text "cbv" ppr (ConcreteTv {}) = text "conc" -- | What caused us to create a 'ConcreteTv' metavariable? -- See Note [ConcreteTv] in GHC.Tc.Utils.Concrete. data ConcreteTvOrigin -- | A 'ConcreteTv' used to enforce the representation-polymorphism invariants. -- -- See 'FixedRuntimeRepOrigin' for more information. = ConcreteFRR FixedRuntimeRepOrigin {- ********************************************************************* * * Untouchable type variables * * ********************************************************************* -} newtype TcLevel = TcLevel Int deriving( Eq, Ord ) -- See Note [TcLevel invariants] for what this Int is -- See also Note [TcLevel assignment] {- Note [TcLevel invariants] ~~~~~~~~~~~~~~~~~~~~~~~~~ * Each unification variable (MetaTv) and skolem (SkolemTv) 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 See Note [GivenInv] (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] The level of a MetaTyVar also governs its untouchability. See Note [Unification preconditions] in GHC.Tc.Utils.Unify. Note [TcLevel assignment] ~~~~~~~~~~~~~~~~~~~~~~~~~ We arrange the TcLevels like this 0 Top level 1 First-level implication constraints 2 Second-level implication constraints ...etc... Note [GivenInv] ~~~~~~~~~~~~~~~ Invariant (GivenInv) is not essential, but it is easy to guarantee, and it is a useful extra piece of structure. It ensures that the Givens of an implication don't change because of unifications /at the same level/ caused by Wanteds. (Wanteds can also cause unifications at an outer level, but that will iterate the entire implication; see GHC.Tc.Solver.Monad Note [The Unification Level Flag].) Givens can certainly contain meta-tyvars from /outer/ levels. E.g. data T a where MkT :: Eq a => a -> MkT a f x = case x of MkT y -> y && True Then we'll infer (x :: T alpha[1]). The Givens from the implication arising from the pattern match will look like this: forall[2] . Eq alpha[1] => (alpha[1] ~ Bool) But if we unify alpha (which in this case we will), we'll iterate the entire implication via Note [The Unification Level Flag] in GHC.Tc.Solver.Monad. That isn't true of unifications at the /ambient/ level. It would be entirely possible to weaken (GivenInv), to LESS THAN OR EQUAL TO, but we'd need to think carefully about - kick-out for Givens - GHC.Tc.Solver.Monad.isOuterTyVar But in fact (GivenInv) is automatically true, so we're adhering to it for now. See #18929. * If a tyvar tv has level n, then the levels of all variables free in tv's kind are <= n. Consequence: if tv is untouchable, so are all variables in tv's kind. 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. -} 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 deeperThanOrSame :: TcLevel -> TcLevel -> Bool deeperThanOrSame (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 invariants] 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 {- ********************************************************************* * * 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 \)... -- we don't need to take \ 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 any_rewritable :: EqRel -- Ambient role -> (EqRel -> TcTyVar -> Bool) -- check tyvar -> (EqRel -> TyCon -> [TcType] -> Bool) -- check type family -> (TyCon -> Bool) -- expand type synonym? -> TcType -> Bool -- Checks every tyvar and tyconapp (not including FunTys) within a type, -- ORing the results of the predicates above together -- Do not look inside casts and coercions -- See Note [anyRewritableTyVar must be role-aware] -- -- This looks like it should use foldTyCo, but that function is -- role-agnostic, and this one must be role-aware. We could make -- foldTyCon role-aware, but that may slow down more common usages. -- -- See Note [Rewritable] in GHC.Tc.Solver.InertSet for a specification for this function. {-# INLINE any_rewritable #-} -- this allows specialization of predicates any_rewritable role tv_pred tc_pred should_expand = go role emptyVarSet where go_tv rl bvs tv | tv `elemVarSet` bvs = False | otherwise = tv_pred rl tv go rl bvs ty@(TyConApp tc tys) | isTypeSynonymTyCon tc , should_expand tc , Just ty' <- tcView ty -- should always match = go rl bvs ty' | tc_pred rl tc tys = True | otherwise = go_tc rl bvs tc tys go rl bvs (TyVarTy tv) = go_tv rl bvs tv go _ _ (LitTy {}) = False 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 _) = go rl bvs ty go _ _ (CoercionTy _) = False 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 anyRewritableTyVar :: EqRel -- Ambient role -> (EqRel -> TcTyVar -> Bool) -- check tyvar -> TcType -> Bool -- See Note [Rewritable] in GHC.Tc.Solver.InertSet for a specification for this function. anyRewritableTyVar role pred = any_rewritable role pred (\ _ _ _ -> False) -- no special check for tyconapps -- (this False is ORed with other results, so it -- really means "do nothing special"; the arguments -- are still inspected) (\ _ -> False) -- don't expand synonyms -- NB: No need to expand synonyms, because we can find -- all free variables of a synonym by looking at its -- arguments anyRewritableTyFamApp :: EqRel -- Ambient role -> (EqRel -> TyCon -> [TcType] -> Bool) -- check tyconapp -- should return True only for type family applications -> TcType -> Bool -- always ignores casts & coercions -- See Note [Rewritable] in GHC.Tc.Solver.InertSet for a specification for this function. anyRewritableTyFamApp role check_tyconapp = any_rewritable role (\ _ _ -> False) check_tyconapp (not . isFamFreeTyCon) {- 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 isPromotableMetaTyVar :: TcTyVar -> Bool -- True is this is a meta-tyvar that can be -- promoted to an outer level isPromotableMetaTyVar tv | isTyVar tv -- See Note [Coercion variables in free variable lists] , MetaTv { mtv_info = info } <- tcTyVarDetails tv = isTouchableInfo info -- Can't promote cycle breakers | otherwise = False 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 , isTouchableInfo info = assertPpr (checkTcLevelInvariant ctxt_tclvl tv_tclvl) (ppr tv $$ ppr tv_tclvl $$ ppr ctxt_tclvl) $ tv_tclvl `sameDepthAs` ctxt_tclvl | otherwise = False isImmutableTyVar :: TyVar -> Bool isImmutableTyVar tv = isSkolemTyVar tv isTyConableTyVar, isSkolemTyVar, isOverlappableTyVar, isMetaTyVar, isAmbiguousTyVar, isCycleBreakerTyVar :: 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 isSkolemTyVar tv = assertPpr (tcIsTcTyVar tv) (ppr tv) $ case tcTyVarDetails tv of MetaTv {} -> False _other -> True skolemSkolInfo :: TcTyVar -> SkolemInfo skolemSkolInfo tv = assert (isSkolemTyVar tv) $ case tcTyVarDetails tv of SkolemTv skol_info _ _ -> skol_info RuntimeUnk -> panic "RuntimeUnk" MetaTv {} -> panic "skolemSkolInfo" 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 RuntimeUnk 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 isCycleBreakerTyVar tv | isTyVar tv -- See Note [Coercion variables in free variable lists] , MetaTv { mtv_info = CycleBreakerTv } <- tcTyVarDetails tv = True | otherwise = False -- | Is this type variable a concrete type variable, i.e. -- it is a metavariable with 'ConcreteTv' 'MetaInfo'? -- -- Returns the 'ConcreteTvOrigin' stored in the type variable -- if so, or 'Nothing' otherwise. isConcreteTyVar_maybe :: TcTyVar -> Maybe ConcreteTvOrigin isConcreteTyVar_maybe tv | isTcTyVar tv , MetaTv { mtv_info = ConcreteTv conc_orig } <- tcTyVarDetails tv = Just conc_orig | otherwise = Nothing -- | Is this type variable a concrete type variable, i.e. -- it is a metavariable with 'ConcreteTv' 'MetaInfo'? isConcreteTyVar :: TcTyVar -> Bool isConcreteTyVar = isJust . isConcreteTyVar_maybe -- | Is this type concrete type variable, i.e. -- a metavariable with 'ConcreteTv' 'MetaInfo'? isConcreteTyVarTy :: TcType -> Bool isConcreteTyVarTy = isJust . isConcreteTyVarTy_maybe -- | Is this type a concrete type variable? If so, return -- the associated 'TcTyVar' and 'ConcreteTvOrigin'. isConcreteTyVarTy_maybe :: TcType -> Maybe (TcTyVar, ConcreteTvOrigin) isConcreteTyVarTy_maybe (TyVarTy tv) = (tv, ) <$> isConcreteTyVar_maybe tv isConcreteTyVarTy_maybe _ = Nothing 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) isTouchableInfo :: MetaInfo -> Bool isTouchableInfo info | CycleBreakerTv <- info = False | otherwise = True 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 -- | Returns the (kind, type) variables in a type that are -- as-yet-unknown: metavariables and RuntimeUnks ambigTkvsOfTy :: TcType -> ([Var],[Var]) ambigTkvsOfTy ty = partition (`elemVarSet` dep_tkv_set) ambig_tkvs where tkvs = tyCoVarsOfTypeList ty ambig_tkvs = filter isAmbiguousTyVar tkvs dep_tkv_set = tyCoVarsOfTypes (map tyVarKind tkvs) {- ************************************************************************ * * 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 getDFunTyLitKey (CharTyLit n) = mkOccName Name.varName (show n) {- ********************************************************************* * * 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 tcSplitForAllTyVarBinder_maybe :: Type -> Maybe (TyVarBinder, Type) tcSplitForAllTyVarBinder_maybe ty | Just ty' <- tcView ty = tcSplitForAllTyVarBinder_maybe ty' tcSplitForAllTyVarBinder_maybe (ForAllTy tv ty) = assert (isTyVarBinder tv ) Just (tv, ty) tcSplitForAllTyVarBinder_maybe _ = Nothing -- | Like 'tcSplitPiTys', but splits off only named binders, -- returning just the tyvars. tcSplitForAllTyVars :: Type -> ([TyVar], Type) tcSplitForAllTyVars ty = assert (all isTyVar (fst sty) ) sty where sty = splitForAllTyCoVars ty -- | Like 'tcSplitForAllTyVars', but only splits 'ForAllTy's with 'Invisible' -- type variable binders. tcSplitForAllInvisTyVars :: Type -> ([TyVar], Type) tcSplitForAllInvisTyVars ty = tcSplitSomeForAllTyVars isInvisibleArgFlag ty -- | Like 'tcSplitForAllTyVars', but only splits a 'ForAllTy' if @argf_pred argf@ -- is 'True', where @argf@ is the visibility of the @ForAllTy@'s binder and -- @argf_pred@ is a predicate over visibilities provided as an argument to this -- function. tcSplitSomeForAllTyVars :: (ArgFlag -> Bool) -> Type -> ([TyVar], Type) tcSplitSomeForAllTyVars argf_pred ty = split ty ty [] where split _ (ForAllTy (Bndr tv argf) ty) tvs | argf_pred argf = split ty ty (tv:tvs) split orig_ty ty tvs | Just ty' <- coreView ty = split orig_ty ty' tvs split orig_ty _ tvs = (reverse tvs, orig_ty) -- | Like 'tcSplitForAllTyVars', but only splits 'ForAllTy's with 'Required' type -- variable binders. All split tyvars are annotated with '()'. tcSplitForAllReqTVBinders :: Type -> ([TcReqTVBinder], Type) tcSplitForAllReqTVBinders ty = assert (all (isTyVar . binderVar) (fst sty) ) sty where sty = splitForAllReqTVBinders ty -- | Like 'tcSplitForAllTyVars', but only splits 'ForAllTy's with 'Invisible' type -- variable binders. All split tyvars are annotated with their 'Specificity'. tcSplitForAllInvisTVBinders :: Type -> ([TcInvisTVBinder], Type) tcSplitForAllInvisTVBinders ty = assert (all (isTyVar . binderVar) (fst sty) ) sty where sty = splitForAllInvisTVBinders ty -- | Like 'tcSplitForAllTyVars', but splits off only named binders. tcSplitForAllTyVarBinders :: Type -> ([TyVarBinder], Type) tcSplitForAllTyVarBinders ty = assert (all isTyVarBinder (fst sty)) sty where sty = splitForAllTyCoVarBinders 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. This only splits /invisible/ type -- variable binders, as these are the only forms of binder that the typechecker -- will implicitly instantiate. tcSplitSigmaTy :: Type -> ([TyVar], ThetaType, Type) tcSplitSigmaTy ty = case tcSplitForAllInvisTyVars ty of (tvs, rho) -> case tcSplitPhiTy rho of (theta, tau) -> (tvs, theta, tau) -- | Split a sigma type into its parts, going underneath as many arrows -- and foralls as possible. See Note [tcSplitNestedSigmaTys] tcSplitNestedSigmaTys :: Type -> ([TyVar], ThetaType, Type) -- See Note [tcSplitNestedSigmaTys] -- NB: This is basically a pure version of deeplyInstantiate (from Unify) that -- doesn't compute an HsWrapper. tcSplitNestedSigmaTys ty -- If there's a forall, split it apart and try splitting the rho type -- underneath it. | (arg_tys, body_ty) <- tcSplitFunTys ty , (tvs1, theta1, rho1) <- tcSplitSigmaTy body_ty , not (null tvs1 && null theta1) = let (tvs2, theta2, rho2) = tcSplitNestedSigmaTys rho1 in (tvs1 ++ tvs2, theta1 ++ theta2, mkVisFunTys arg_tys rho2) -- If there's no forall, we're done. | otherwise = ([], [], ty) {- Note [tcSplitNestedSigmaTys] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ tcSplitNestedSigmaTys splits out all the /nested/ foralls and constraints, including under function arrows. E.g. given this type synonym: type Traversal s t a b = forall f. Applicative f => (a -> f b) -> s -> f t then tcSplitNestedSigmaTys (forall s t a b. C s t a b => Int -> Traversal s t a b) will return ( [s,t,a,b,f] , [C s t a b, Applicative f] , Int -> (a -> f b) -> s -> f t)@. This function is used in these places: * Improving error messages in GHC.Tc.Gen.Head.addFunResCtxt * Validity checking for default methods: GHC.Tc.TyCl.checkValidClass * A couple of calls in the GHCi debugger: GHC.Runtime.Heap.Inspect In other words, just in validity checking and error messages; hence no wrappers or evidence generation. Notice that tcSplitNestedSigmaTys even looks under function arrows; doing so is the Right Thing even with simple subsumption, not just with deep subsumption. -} ----------------------- 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 tcSplitForAllInvisTyVars 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) <- tcSplitForAllInvisTyVars 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 implements typechecker equality, as described in -- @Note [Typechecker equality vs definitional equality]@. tcEqType ty1 ty2 = tcEqTypeNoSyns ki1 ki2 && tcEqTypeNoSyns 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 = tcEqTypeNoSyns ty1 ty2 -- | Check whether two TyConApps are the same; if the number of arguments -- are different, just checks the common prefix of arguments. tcEqTyConApps :: TyCon -> [Type] -> TyCon -> [Type] -> Bool tcEqTyConApps tc1 args1 tc2 args2 = tc1 == tc2 && and (zipWith tcEqTypeNoKindCheck args1 args2) -- No kind check necessary: if both arguments are well typed, then -- any difference in the kinds of later arguments would show up -- as differences in earlier (dependent) arguments {- Note [Specialising tc_eq_type] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The type equality predicates in TcType are hit pretty hard during typechecking. Consequently we take pains to ensure that these paths are compiled to efficient, minimally-allocating code. To this end we place an INLINE on tc_eq_type, ensuring that it is inlined into its publicly-visible interfaces (e.g. tcEqType). In addition to eliminating some dynamic branches, this allows the simplifier to eliminate the closure allocations that would otherwise be necessary to capture the two boolean "mode" flags. This reduces allocations by a good fraction of a percent when compiling Cabal. See #19226. -} -- | Type equality comparing both visible and invisible arguments and expanding -- type synonyms. tcEqTypeNoSyns :: TcType -> TcType -> Bool tcEqTypeNoSyns ta tb = tc_eq_type False False ta tb -- | 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 -- See Note [Computing equality on types] in 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 -- See Note [Comparing nullary type synonyms] in GHC.Core.Type. go _ (TyConApp tc1 []) (TyConApp tc2 []) | tc1 == tc2 = True 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 `sameVis` vis2 -- See Note [ForAllTy and typechecker equality] in -- GHC.Tc.Solver.Canonical for why we use `sameVis` here && (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. -- See Note [Equality on FunTys] in GHC.Core.TyCo.Rep: we must check -- kinds here go env (FunTy _ w1 arg1 res1) (FunTy _ w2 arg2 res2) = kinds_eq && go env arg1 arg2 && go env res1 res2 && go env w1 w2 where kinds_eq | vis_only = True | otherwise = go env (typeKind arg1) (typeKind arg2) && go env (typeKind res1) (typeKind res2) -- 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] {-# INLINE tc_eq_type #-} -- See Note [Specialising tc_eq_type]. {- Note [Typechecker equality vs definitional equality] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ GHC has two notions of equality over Core types: * Definitional equality, as implemented by GHC.Core.Type.eqType. See Note [Non-trivial definitional equality] in GHC.Core.TyCo.Rep. * Typechecker equality, as implemented by tcEqType (in GHC.Tc.Utils.TcType). GHC.Tc.Solver.Canonical.canEqNC also respects typechecker equality. Typechecker equality implies definitional equality: if two types are equal according to typechecker equality, then they are also equal according to definitional equality. The converse is not always true, as typechecker equality is more finer-grained than definitional equality in two places: * Unlike definitional equality, which equates Type and Constraint, typechecker treats them as distinct types. See Note [Kind Constraint and kind Type] in GHC.Core.Type. * Unlike definitional equality, which does not care about the ArgFlag of a ForAllTy, typechecker equality treats Required type variable binders as distinct from Invisible type variable binders. See Note [ForAllTy and typechecker equality] in GHC.Tc.Solver.Canonical. -} {- ********************************************************************* * * 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. --------------------------- 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 = isIPLikePred 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, implicants 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 -- Why look at work-list too? Suppose work_item is Eq a, -- and work-list contains Ord a = 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 ] implicants pred = pred : eq_extras pred ++ transSuperClasses pred -- Combine (a ~ b) and (b ~ a); no need to have both in one context -- These can arise when dealing with partial type signatures (e.g. T14715) eq_extras pred = case classifyPredType pred of EqPred r t1 t2 -> [mkPrimEqPredRole (eqRelRole r) t2 t1] ClassPred cls [k1,k2,t1,t2] | cls `hasKey` heqTyConKey -> [mkClassPred cls [k2, k1, t2, t1]] ClassPred cls [k,t1,t2] | cls `hasKey` eqTyConKey -> [mkClassPred cls [k, t2, t1]] _ -> [] 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 {- 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. ************************************************************************ * * 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, isFloatPrimTy, isDoublePrimTy, isIntegerTy, isNaturalTy, isIntTy, isWordTy, isBoolTy, isUnitTy, isCharTy, isAnyTy :: Type -> Bool isFloatTy = is_tc floatTyConKey isDoubleTy = is_tc doubleTyConKey isFloatPrimTy = is_tc floatPrimTyConKey isDoublePrimTy = is_tc doublePrimTyConKey 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 -- | Is the type inhabited by machine floating-point numbers? -- -- Used to check that we don't use floating-point literal patterns -- in Core. -- -- See #9238 and Note [Rules for floating-point comparisons] -- in GHC.Core.Opt.ConstantFold. isFloatingPrimTy :: Type -> Bool isFloatingPrimTy ty = isFloatPrimTy ty || isDoublePrimTy 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_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 isRigidTy :: TcType -> Bool isRigidTy ty | Just (tc,_) <- tcSplitTyConApp_maybe ty = isGenerativeTyCon tc Nominal | Just {} <- tcSplitAppTy_maybe ty = True | isForAllTy ty = True | otherwise = False {- ************************************************************************ * * 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 -- | Reason why a type in an FFI signature is invalid data IllegalForeignTypeReason = TypeCannotBeMarshaled !Type TypeCannotBeMarshaledReason | ForeignDynNotPtr !Type -- ^ Expected type !Type -- ^ Actual type | SafeHaskellMustBeInIO | IOResultExpected | UnexpectedNestedForall | LinearTypesNotAllowed | OneArgExpected | AtLeastOneArgExpected -- | Reason why a type cannot be marshalled through the FFI. data TypeCannotBeMarshaledReason = NotADataType | NewtypeDataConNotInScope !(Maybe TyCon) | UnliftedFFITypesNeeded | NotABoxedMarshalableTyCon | ForeignLabelNotAPtr | NotSimpleUnliftedType isFFIArgumentTy :: DynFlags -> Safety -> Type -> Validity' IllegalForeignTypeReason -- Checks for valid argument type for a 'foreign import' isFFIArgumentTy dflags safety ty = checkRepTyCon (legalOutgoingTyCon dflags safety) ty isFFIExternalTy :: Type -> Validity' IllegalForeignTypeReason -- Types that are allowed as arguments of a 'foreign export' isFFIExternalTy ty = checkRepTyCon legalFEArgTyCon ty isFFIImportResultTy :: DynFlags -> Type -> Validity' IllegalForeignTypeReason isFFIImportResultTy dflags ty = checkRepTyCon (legalFIResultTyCon dflags) ty isFFIExportResultTy :: Type -> Validity' IllegalForeignTypeReason isFFIExportResultTy ty = checkRepTyCon legalFEResultTyCon ty isFFIDynTy :: Type -> Type -> Validity' IllegalForeignTypeReason -- 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 (ForeignDynNotPtr expected ty) isFFILabelTy :: Type -> Validity' IllegalForeignTypeReason -- 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 ForeignLabelNotAPtr isFFIPrimArgumentTy :: DynFlags -> Type -> Validity' IllegalForeignTypeReason -- 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' IllegalForeignTypeReason -- 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' TypeCannotBeMarshaledReason) -> Type -> Validity' IllegalForeignTypeReason checkRepTyCon check_tc ty = fmap (TypeCannotBeMarshaled ty) $ case splitTyConApp_maybe ty of Just (tc, tys) | isNewTyCon tc -> NotValid (mk_nt_reason tc tys) | otherwise -> check_tc tc Nothing -> NotValid NotADataType where mk_nt_reason tc tys | null tys = NewtypeDataConNotInScope Nothing | otherwise = NewtypeDataConNotInScope (Just tc) {- 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' TypeCannotBeMarshaledReason 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' TypeCannotBeMarshaledReason legalFIResultTyCon dflags tc | tc == unitTyCon = IsValid | otherwise = marshalableTyCon dflags tc legalFEResultTyCon :: TyCon -> Validity' TypeCannotBeMarshaledReason legalFEResultTyCon tc | tc == unitTyCon = IsValid | otherwise = boxedMarshalableTyCon tc legalOutgoingTyCon :: DynFlags -> Safety -> TyCon -> Validity' TypeCannotBeMarshaledReason -- Checks validity of types going from Haskell -> external world legalOutgoingTyCon dflags _ tc = marshalableTyCon dflags tc -- Check for marshalability of a primitive type. -- We exclude lifted types such as RealWorld and TYPE. -- They can technically appear in types, e.g. -- f :: RealWorld -> TYPE LiftedRep -> RealWorld -- f x _ = x -- but there are no values of type RealWorld or TYPE LiftedRep, -- so it doesn't make sense to use them in FFI. marshalablePrimTyCon :: TyCon -> Bool marshalablePrimTyCon tc = isPrimTyCon tc && not (isLiftedTypeKind (tyConResKind tc)) marshalableTyCon :: DynFlags -> TyCon -> Validity' TypeCannotBeMarshaledReason marshalableTyCon dflags tc | marshalablePrimTyCon tc , not (null (tyConPrimRep tc)) -- Note [Marshalling void] = validIfUnliftedFFITypes dflags | otherwise = boxedMarshalableTyCon tc boxedMarshalableTyCon :: TyCon -> Validity' TypeCannotBeMarshaledReason 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 NotABoxedMarshalableTyCon legalFIPrimArgTyCon :: DynFlags -> TyCon -> Validity' TypeCannotBeMarshaledReason -- Check args of 'foreign import prim', only allow simple unlifted types. legalFIPrimArgTyCon dflags tc | marshalablePrimTyCon tc = validIfUnliftedFFITypes dflags | otherwise = NotValid NotSimpleUnliftedType legalFIPrimResultTyCon :: DynFlags -> TyCon -> Validity' TypeCannotBeMarshaledReason -- Check result type of 'foreign import prim'. Allow simple unlifted -- types and also unboxed tuple and sum result types. legalFIPrimResultTyCon dflags tc | marshalablePrimTyCon tc , not (null (tyConPrimRep tc)) -- Note [Marshalling void] = validIfUnliftedFFITypes dflags | isUnboxedTupleTyCon tc || isUnboxedSumTyCon tc = validIfUnliftedFFITypes dflags | otherwise = NotValid $ NotSimpleUnliftedType validIfUnliftedFFITypes :: DynFlags -> Validity' TypeCannotBeMarshaledReason validIfUnliftedFFITypes dflags | xopt LangExt.UnliftedFFITypes dflags = IsValid | otherwise = NotValid UnliftedFFITypesNeeded {- 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