{- (c) The University of Glasgow 2006 (c) The GRASP/AQUA Project, Glasgow University, 1992-1998 \section[TcType]{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 The "tc" prefix is for "TypeChecker", because the type checker is the principal client. -} {-# LANGUAGE CPP, MultiWayIf #-} module TcType ( -------------------------------- -- Types TcType, TcSigmaType, TcRhoType, TcTauType, TcPredType, TcThetaType, TcTyVar, TcTyVarSet, TcDTyVarSet, TcTyCoVarSet, TcDTyCoVarSet, TcKind, TcCoVar, TcTyCoVar, TcTyBinder, TcTyCon, ExpType(..), ExpSigmaType, ExpRhoType, mkCheckExpType, SyntaxOpType(..), synKnownType, mkSynFunTys, -- TcLevel TcLevel(..), topTcLevel, pushTcLevel, isTopTcLevel, strictlyDeeperThan, sameDepthAs, fmvTcLevel, -------------------------------- -- MetaDetails UserTypeCtxt(..), pprUserTypeCtxt, pprSigCtxt, isSigMaybe, TcTyVarDetails(..), pprTcTyVarDetails, vanillaSkolemTv, superSkolemTv, MetaDetails(Flexi, Indirect), MetaInfo(..), TauTvFlavour(..), isImmutableTyVar, isSkolemTyVar, isMetaTyVar, isMetaTyVarTy, isTyVarTy, isSigTyVar, isOverlappableTyVar, isTyConableTyVar, isFskTyVar, isFmvTyVar, isFlattenTyVar, isAmbiguousTyVar, metaTvRef, metaTyVarInfo, isFlexi, isIndirect, isRuntimeUnkSkol, metaTyVarTcLevel, setMetaTyVarTcLevel, metaTyVarTcLevel_maybe, isTouchableMetaTyVar, isTouchableOrFmv, isFloatedTouchableMetaTyVar, canUnifyWithPolyType, -------------------------------- -- Builders mkPhiTy, mkInvSigmaTy, mkSpecSigmaTy, mkSigmaTy, mkNakedTyConApp, mkNakedAppTys, mkNakedAppTy, mkNakedCastTy, -------------------------------- -- Splitters -- These are important because they do not look through newtypes getTyVar, tcSplitForAllTy_maybe, tcSplitForAllTys, tcSplitPiTys, tcSplitNamedPiTys, tcSplitPhiTy, tcSplitPredFunTy_maybe, tcSplitFunTy_maybe, tcSplitFunTys, tcFunArgTy, tcFunResultTy, tcSplitFunTysN, tcSplitTyConApp, tcSplitTyConApp_maybe, tcRepSplitTyConApp_maybe, tcTyConAppTyCon, tcTyConAppArgs, tcSplitAppTy_maybe, tcSplitAppTy, tcSplitAppTys, tcRepSplitAppTy_maybe, tcGetTyVar_maybe, tcGetTyVar, nextRole, tcSplitSigmaTy, tcDeepSplitSigmaTy_maybe, --------------------------------- -- Predicates. -- Again, newtypes are opaque eqType, eqTypes, cmpType, cmpTypes, eqTypeX, pickyEqType, tcEqType, tcEqKind, tcEqTypeNoKindCheck, tcEqTypeVis, isSigmaTy, isRhoTy, isRhoExpTy, isOverloadedTy, isFloatingTy, isDoubleTy, isFloatTy, isIntTy, isWordTy, isStringTy, isIntegerTy, isBoolTy, isUnitTy, isCharTy, isCallStackTy, isCallStackPred, isTauTy, isTauTyCon, tcIsTyVarTy, tcIsForAllTy, isPredTy, isTyVarClassPred, isTyVarExposed, isTyVarUnderDatatype, checkValidClsArgs, hasTyVarHead, isRigidEqPred, isRigidTy, --------------------------------- -- Misc type manipulators deNoteType, occurCheckExpand, OccCheckResult(..), orphNamesOfType, orphNamesOfCo, orphNamesOfTypes, orphNamesOfCoCon, getDFunTyKey, evVarPred_maybe, evVarPred, --------------------------------- -- Predicate types mkMinimalBySCs, transSuperClasses, pickQuantifiablePreds, immSuperClasses, isImprovementPred, -- * Finding type instances tcTyFamInsts, -- * Finding "exact" (non-dead) type variables exactTyCoVarsOfType, exactTyCoVarsOfTypes, splitDepVarsOfType, splitDepVarsOfTypes, TcDepVars(..), depVarsTyVars, -- * Extracting bound variables allBoundVariables, allBoundVariabless, --------------------------------- -- 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 -------------------------------- -- Rexported from Kind Kind, typeKind, liftedTypeKind, constraintKind, isLiftedTypeKind, isUnliftedTypeKind, classifiesTypeWithValues, -------------------------------- -- Rexported from Type Type, PredType, ThetaType, TyBinder, VisibilityFlag(..), mkForAllTy, mkForAllTys, mkInvForAllTys, mkSpecForAllTys, mkNamedForAllTy, mkFunTy, mkFunTys, mkTyConApp, mkAppTy, mkAppTys, mkTyConTy, mkTyVarTy, mkTyVarTys, mkNamedBinder, isClassPred, isEqPred, isNomEqPred, isIPPred, mkClassPred, isDictLikeTy, tcSplitDFunTy, tcSplitDFunHead, isRuntimeRepVar, isRuntimeRepPolymorphic, isVisibleBinder, isInvisibleBinder, -- Type substitutions TCvSubst(..), -- Representation visible to a few friends TvSubstEnv, emptyTCvSubst, 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, substTyWith, substTyWithCoVars, substTyAddInScope, substTyUnchecked, substTysUnchecked, substThetaUnchecked, substTyWithBindersUnchecked, substTyWithUnchecked, substCoUnchecked, substCoWithUnchecked, substTheta, isUnliftedType, -- Source types are always lifted isUnboxedTupleType, -- Ditto isPrimitiveType, coreView, tyCoVarsOfType, tyCoVarsOfTypes, closeOverKinds, tyCoVarsOfTelescope, tyCoFVsOfType, tyCoFVsOfTypes, tyCoVarsOfTypeDSet, tyCoVarsOfTypesDSet, closeOverKindsDSet, tyCoVarsOfTypeList, tyCoVarsOfTypesList, -------------------------------- -- Transforming Types to TcTypes toTcType, -- :: Type -> TcType toTcTypeBag, -- :: Bag EvVar -> Bag EvVar pprKind, pprParendKind, pprSigmaType, pprType, pprParendType, pprTypeApp, pprTyThingCategory, pprTheta, pprThetaArrowTy, pprClassPred, pprTvBndr, pprTvBndrs, TypeSize, sizeType, sizeTypes, toposortTyVars ) where #include "HsVersions.h" -- friends: import Kind import TyCoRep import Class import Var import ForeignCall import VarSet import Coercion import Type import TyCon -- others: import DynFlags import CoreFVs import Name -- hiding (varName) -- We use this to make dictionaries for type literals. -- Perhaps there's a better way to do this? import NameSet import VarEnv import PrelNames import TysWiredIn import BasicTypes import Util import Bag import Maybes import Pair import Outputable import FastString import ErrUtils( Validity(..), MsgDoc, isValid ) import FV import qualified GHC.LanguageExtensions as LangExt import Data.IORef import Control.Monad (liftM, ap) #if __GLASGOW_HASKELL__ < 709 import Data.Monoid (mempty, mappend) import Data.Foldable (foldMap) import Control.Applicative (Applicative(..), (<$>) ) #endif import Data.Functor.Identity {- ************************************************************************ * * \subsection{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. -} type TcTyVar = TyVar -- Used only during type inference 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 TcTyBinder = TyBinder 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 -- | An expected type to check against during type-checking. -- See Note [ExpType] in TcMType, where you'll also find manipulators. data ExpType = Check TcType | Infer Unique -- for debugging only TcLevel -- See Note [TcLevel of ExpType] in TcMType Kind (IORef (Maybe TcType)) type ExpSigmaType = ExpType type ExpRhoType = ExpType instance Outputable ExpType where ppr (Check ty) = ppr ty ppr (Infer u lvl ki _) = parens (text "Infer" <> braces (ppr u <> comma <> ppr lvl) <+> dcolon <+> ppr ki) -- | Make an 'ExpType' suitable for checking. mkCheckExpType :: TcType -> ExpType mkCheckExpType = Check -- | 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. -- -- This is defined here to avoid defining it in TcExpr.hs-boot. data SyntaxOpType = SynAny -- ^ Any type | SynRho -- ^ A rho type, deeply 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, or to the right of an arrow YES (forall a. a->a) -> Int NO forall a. a -> Int NO Eq a => a -> a NO Int -> forall a. a -> Int ************************************************************************ * * \subsection{TyVarDetails} * * ************************************************************************ 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 Var.hs. There is no reason in principle why Var.hs shouldn't actually have the definition, but it "belongs" here. Note [Signature skolems] ~~~~~~~~~~~~~~~~~~~~~~~~ Consider this f :: forall a. [a] -> Int f (x::b : xs) = 3 Here 'b' is a lexically scoped type variable, but it turns out to be the same as the skolem 'a'. So we have a special kind of skolem constant, SigTv, which can unify with other SigTvs. They are used *only* for pattern type signatures. Similarly consider 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 SigTvs 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 Bool -- True <=> this skolem type variable can be overlapped -- when looking up instances -- See Note [Binding when looking up instances] in InstEnv | FlatSkol -- A flatten-skolem. It stands for the TcType, and zonking TcType -- will replace it by that type. -- See Note [The flattening story] in TcFlatten | 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 InstEnv vanillaSkolemTv = SkolemTv False -- Might be instantiated superSkolemTv = SkolemTv True -- Treat this as a completely distinct type ----------------------------- data MetaDetails = Flexi -- Flexi type variables unify to become Indirects | Indirect TcType instance Outputable MetaDetails where ppr Flexi = text "Flexi" ppr (Indirect ty) = text "Indirect" <+> ppr ty data TauTvFlavour = VanillaTau | WildcardTau -- ^ A tyvar that originates from a type wildcard. 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. | SigTv -- A variant of TauTv, except that it should not be -- unified with a type, only with a type variable -- SigTvs are only distinguished to improve error messages -- see Note [Signature skolems] -- The MetaDetails, if filled in, will -- always be another SigTv or a SkolemTv | FlatMetaTv -- A flatten meta-tyvar -- It is a meta-tyvar, but it is always untouchable, with level 0 -- See Note [The flattening story] in TcFlatten ------------------------------------- -- UserTypeCtxt describes the origin of the polymorphic type -- in the places where we need to an expression has that type data UserTypeCtxt = FunSigCtxt -- Function type signature, when checking the type -- Also used for types in SPECIALISE pragmas Name -- Name of the function Bool -- True <=> report redundant constraints -- This is usually True, but False for -- * Record selectors (not important here) -- * Class and instance methods. Here -- the code may legitimately be more -- polymorphic than the signature -- generated from the class -- declaration | InfSigCtxt Name -- Inferred type for function | ExprSigCtxt -- Expression type signature | TypeAppCtxt -- Visible type application | ConArgCtxt Name -- Data constructor argument | TySynCtxt Name -- RHS of a type synonym decl | PatSynBuilderCtxt Name -- Type sig for the builder of a bidirectional pattern synonym | PatSigCtxt -- Type sig in pattern -- eg f (x::t) = ... -- or (x::t, y) = e | RuleSigCtxt Name -- LHS of a RULE forall -- RULE "foo" forall (x :: a -> a). f (Just x) = ... | ResSigCtxt -- Result type sig -- f x :: t = .... | ForSigCtxt Name -- Foreign import or export signature | DefaultDeclCtxt -- Types in a default declaration | InstDeclCtxt -- An instance declaration | SpecInstCtxt -- SPECIALISE instance pragma | ThBrackCtxt -- Template Haskell type brackets [t| ... |] | GenSigCtxt -- Higher-rank or impredicative situations -- e.g. (f e) where f has a higher-rank type -- We might want to elaborate this | GhciCtxt -- GHCi command :kind | ClassSCCtxt Name -- Superclasses of a class | SigmaCtxt -- Theta part of a normal for-all type -- f :: => a -> a | DataTyCtxt Name -- Theta part of a data decl -- data => T a = MkT a {- -- Notes re TySynCtxt -- We allow type synonyms that aren't types; e.g. type List = [] -- -- If the RHS mentions tyvars that aren't in scope, we'll -- quantify over them: -- e.g. type T = a->a -- will become type T = forall a. a->a -- -- With gla-exts that's right, but for H98 we should complain. -} {- ********************************************************************* * * Untoucable 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 of an Implication is STRICTLY GREATER THAN that of its parent (MetaTvInv) The level number of a unification variable is LESS THAN OR EQUAL TO that of its parent implication * A unification variable is *touchable* if its level number is EQUAL TO that of its immediate parent implication. * INVARIANT (GivenInv) The free variables of the ic_given of an implication are all untouchable; ie their level numbers are LESS THAN the ic_tclvl of the implication Note [Skolem escape prevention] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ We only unify touchable unification variables. Because of (MetaTvInv), 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 1 Top level 2 Flatten-meta-vars of level 3 3 First-level implication constraints 4 Flatten-meta-vars of level 5 5 Second-level implication constraints ...etc... The even-numbered levels are for the flatten-meta-variables assigned at the next level in. Eg for a second-level implication conststraint (level 5), the flatten meta-vars are level 4, which makes them untouchable. The flatten meta-vars could equally well all have level 0, or just NotALevel since they do not live across implications. -} fmvTcLevel :: TcLevel -> TcLevel -- See Note [TcLevel assignment] fmvTcLevel (TcLevel n) = TcLevel (n-1) topTcLevel :: TcLevel -- See Note [TcLevel assignment] topTcLevel = TcLevel 1 -- 1 = outermost level isTopTcLevel :: TcLevel -> Bool isTopTcLevel (TcLevel 1) = True isTopTcLevel _ = False pushTcLevel :: TcLevel -> TcLevel -- See Note [TcLevel assignment] pushTcLevel (TcLevel us) = TcLevel (us + 2) 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 (MetaTvInv) from Note [TcLevel and untouchable type variables] checkTcLevelInvariant (TcLevel ctxt_tclvl) (TcLevel tv_tclvl) = ctxt_tclvl >= tv_tclvl instance Outputable TcLevel where ppr (TcLevel us) = ppr us {- ************************************************************************ * * Pretty-printing * * ************************************************************************ -} pprTcTyVarDetails :: TcTyVarDetails -> SDoc -- For debugging pprTcTyVarDetails (SkolemTv True) = text "ssk" pprTcTyVarDetails (SkolemTv False) = text "sk" pprTcTyVarDetails (RuntimeUnk {}) = text "rt" pprTcTyVarDetails (FlatSkol {}) = text "fsk" pprTcTyVarDetails (MetaTv { mtv_info = info, mtv_tclvl = tclvl }) = pp_info <> colon <> ppr tclvl where pp_info = case info of TauTv -> text "tau" SigTv -> text "sig" FlatMetaTv -> text "fuv" pprUserTypeCtxt :: UserTypeCtxt -> SDoc pprUserTypeCtxt (FunSigCtxt n _) = text "the type signature for" <+> quotes (ppr n) pprUserTypeCtxt (InfSigCtxt n) = text "the inferred type for" <+> quotes (ppr n) pprUserTypeCtxt (RuleSigCtxt n) = text "a RULE for" <+> quotes (ppr n) pprUserTypeCtxt ExprSigCtxt = text "an expression type signature" pprUserTypeCtxt TypeAppCtxt = text "a type argument" pprUserTypeCtxt (ConArgCtxt c) = text "the type of the constructor" <+> quotes (ppr c) pprUserTypeCtxt (TySynCtxt c) = text "the RHS of the type synonym" <+> quotes (ppr c) pprUserTypeCtxt ThBrackCtxt = text "a Template Haskell quotation [t|...|]" pprUserTypeCtxt PatSigCtxt = text "a pattern type signature" pprUserTypeCtxt ResSigCtxt = text "a result type signature" pprUserTypeCtxt (ForSigCtxt n) = text "the foreign declaration for" <+> quotes (ppr n) pprUserTypeCtxt DefaultDeclCtxt = text "a type in a `default' declaration" pprUserTypeCtxt InstDeclCtxt = text "an instance declaration" pprUserTypeCtxt SpecInstCtxt = text "a SPECIALISE instance pragma" pprUserTypeCtxt GenSigCtxt = text "a type expected by the context" pprUserTypeCtxt GhciCtxt = text "a type in a GHCi command" pprUserTypeCtxt (ClassSCCtxt c) = text "the super-classes of class" <+> quotes (ppr c) pprUserTypeCtxt SigmaCtxt = text "the context of a polymorphic type" pprUserTypeCtxt (DataTyCtxt tc) = text "the context of the data type declaration for" <+> quotes (ppr tc) pprUserTypeCtxt (PatSynBuilderCtxt n) = vcat [ text "the type signature for bidirectional pattern synonym" <+> quotes (ppr n) , text "when used in an expression context" ] pprSigCtxt :: UserTypeCtxt -> SDoc -> SDoc -> SDoc -- (pprSigCtxt ctxt ) -- prints In the type signature for 'f': -- f :: -- The is either empty or "the ambiguity check for" pprSigCtxt ctxt extra pp_ty | Just n <- isSigMaybe ctxt = vcat [ text "In" <+> extra <+> ptext (sLit "the type signature:") , nest 2 (pprPrefixOcc n <+> dcolon <+> pp_ty) ] | otherwise = hang (text "In" <+> extra <+> pprUserTypeCtxt ctxt <> colon) 2 pp_ty where isSigMaybe :: UserTypeCtxt -> Maybe Name isSigMaybe (FunSigCtxt n _) = Just n isSigMaybe (ConArgCtxt n) = Just n isSigMaybe (ForSigCtxt n) = Just n isSigMaybe (PatSynBuilderCtxt n) = Just n isSigMaybe _ = Nothing {- ************************************************************************ * * Finding type family instances * * ************************************************************************ -} -- | Finds outermost type-family applications occuring in a type, -- after expanding synonyms. tcTyFamInsts :: Type -> [(TyCon, [Type])] tcTyFamInsts ty | Just exp_ty <- coreView ty = tcTyFamInsts exp_ty tcTyFamInsts (TyVarTy _) = [] tcTyFamInsts (TyConApp tc tys) | isTypeFamilyTyCon tc = [(tc, tys)] | otherwise = concat (map tcTyFamInsts tys) tcTyFamInsts (LitTy {}) = [] tcTyFamInsts (ForAllTy bndr ty) = tcTyFamInsts (binderType bndr) ++ tcTyFamInsts ty tcTyFamInsts (AppTy ty1 ty2) = tcTyFamInsts ty1 ++ tcTyFamInsts ty2 tcTyFamInsts (CastTy ty _) = tcTyFamInsts ty tcTyFamInsts (CoercionTy _) = [] -- don't count tyfams in coercions, -- as they never get normalized, anyway {- ************************************************************************ * * 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! Here's the example that Ralf Laemmel showed me: foo :: (forall a. C u a -> C u a) -> u mappend :: Monoid u => u -> u -> u bar :: Monoid u => u bar = foo (\t -> t `mappend` t) We have to generalise at the arg to f, and we don't want to capture the constraint (Monad (C u a)) because it appears to mention a. Pretty silly, but it was useful to him. exactTyCoVarsOfType is used by the type checker to figure out exactly which type variables are mentioned in a type. It's also used in the smart-app checking code --- see TcExpr.tcIdApp On the other hand, consider a *top-level* definition f = (\x -> x) :: T a -> T a If we don't abstract over 'a' it'll get fixed to GHC.Prim.Any, and then if we have an application like (f "x") we get a confusing error message involving Any. So the conclusion is this: when generalising - at top level use tyCoVarsOfType - in nested bindings use exactTyCoVarsOfType See Trac #1813 for example. -} exactTyCoVarsOfType :: Type -> TyCoVarSet -- Find the free type variables (of any kind) -- but *expand* type synonyms. See Note [Silly type synonym] above. exactTyCoVarsOfType ty = go ty where go ty | Just ty' <- coreView ty = go ty' -- This is the key line go (TyVarTy tv) = unitVarSet tv `unionVarSet` go (tyVarKind tv) go (TyConApp _ tys) = exactTyCoVarsOfTypes tys go (LitTy {}) = emptyVarSet go (AppTy fun arg) = go fun `unionVarSet` go arg go (ForAllTy bndr ty) = delBinderVar (go ty) bndr `unionVarSet` go (binderType bndr) go (CastTy ty co) = go ty `unionVarSet` goCo co go (CoercionTy co) = goCo co goCo (Refl _ ty) = go ty goCo (TyConAppCo _ _ args)= goCos args goCo (AppCo co arg) = goCo co `unionVarSet` goCo arg goCo (ForAllCo tv k_co co) = goCo co `delVarSet` tv `unionVarSet` goCo k_co goCo (CoVarCo v) = unitVarSet v `unionVarSet` go (varType v) goCo (AxiomInstCo _ _ args) = goCos args goCo (UnivCo p _ t1 t2) = goProv p `unionVarSet` go t1 `unionVarSet` go t2 goCo (SymCo co) = goCo co goCo (TransCo co1 co2) = goCo co1 `unionVarSet` goCo co2 goCo (NthCo _ co) = goCo co goCo (LRCo _ co) = goCo co goCo (InstCo co arg) = goCo co `unionVarSet` goCo arg goCo (CoherenceCo c1 c2) = goCo c1 `unionVarSet` goCo c2 goCo (KindCo co) = goCo co goCo (SubCo co) = goCo co goCo (AxiomRuleCo _ c) = goCos c goCos cos = foldr (unionVarSet . goCo) emptyVarSet cos goProv UnsafeCoerceProv = emptyVarSet goProv (PhantomProv kco) = goCo kco goProv (ProofIrrelProv kco) = goCo kco goProv (PluginProv _) = emptyVarSet goProv (HoleProv _) = emptyVarSet exactTyCoVarsOfTypes :: [Type] -> TyVarSet exactTyCoVarsOfTypes tys = mapUnionVarSet exactTyCoVarsOfType tys {- ************************************************************************ * * Bound variables in a type * * ************************************************************************ -} -- | Find all variables bound anywhere in a type. -- See also Note [Scope-check inferred kinds] in TcHsType allBoundVariables :: Type -> TyVarSet allBoundVariables ty = fvVarSet $ go ty where go :: Type -> FV go (TyVarTy tv) = go (tyVarKind tv) go (TyConApp _ tys) = mapUnionFV go tys go (AppTy t1 t2) = go t1 `unionFV` go t2 go (ForAllTy (Anon t1) t2) = go t1 `unionFV` go t2 go (ForAllTy (Named tv _) t2) = FV.unitFV tv `unionFV` go (tyVarKind tv) `unionFV` go t2 go (LitTy {}) = emptyFV go (CastTy ty _) = go ty go (CoercionTy {}) = emptyFV -- any types mentioned in a coercion should also be mentioned in -- a type. allBoundVariabless :: [Type] -> TyVarSet allBoundVariabless = mapUnionVarSet allBoundVariables {- ************************************************************************ * * Predicates * * ************************************************************************ -} isTouchableOrFmv :: TcLevel -> TcTyVar -> Bool {- ********************************************************************* * * Type and kind variables in a type * * ********************************************************************* -} data TcDepVars -- See Note [Dependent type variables] -- See Note [TcDepVars determinism] = DV { dv_kvs :: DTyCoVarSet -- "kind" variables (dependent) , dv_tvs :: DTyVarSet -- "type" variables (non-dependent) -- The two are disjoint sets } depVarsTyVars :: TcDepVars -> DTyVarSet depVarsTyVars = dv_tvs instance Outputable TcDepVars where ppr (DV {dv_kvs = kvs, dv_tvs = tvs }) = text "DV" <+> braces (sep [ text "dv_kvs =" <+> ppr kvs , text "dv_tvs =" <+> ppr tvs ]) {- Note [Dependent type variables] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ In Haskell type inference we quantify over type variables; but we only quantify over /kind/ variables when -XPolyKinds is on. So when collecting the free vars of a type, prior to quantifying, we must keep the type and kind veraibles separate. But what does that mean in a system where kind variables /are/ type variables? It's a fairly arbitrary distinction based on how the variables appear: - "Kind variables" appear in the kind of some other free variable PLUS any free coercion variables - "Type variables" are all free vars that are not kind variables E.g. In the type T k (a::k) 'k' is a kind variable, because it occurs in the kind of 'a', even though it also appears at "top level" of the type 'a' is a type variable, becuase it doesn't Note that * We include any coercion variables in the "dependent", "kind-variable" set because we never quantify over them. * Both sets are un-ordered, of course. * The "kind variables" might depend on each other; e.g (k1 :: k2), (k2 :: *) The "type variables" do not depend on each other; if one did, it'd be classified as a kind variable! Note [TcDepVars determinism] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~ When we quantify over type variables we decide the order in which they appear in the final type. Because the order of type variables in the type can end up in the interface file and affects some optimizations like worker-wrapper we want this order to be deterministic. To achieve that we use deterministic sets of variables that can be converted to lists in a deterministic order. For more information about deterministic sets see Note [Deterministic UniqFM] in UniqDFM. -} splitDepVarsOfType :: Type -> TcDepVars -- See Note [Dependent type variables] splitDepVarsOfType ty = DV { dv_kvs = dep_vars , dv_tvs = nondep_vars `minusDVarSet` dep_vars } where Pair dep_vars nondep_vars = split_dep_vars ty -- | Like 'splitDepVarsOfType', but over a list of types splitDepVarsOfTypes :: [Type] -> TcDepVars -- See Note [Dependent type variables] splitDepVarsOfTypes tys = DV { dv_kvs = dep_vars , dv_tvs = nondep_vars `minusDVarSet` dep_vars } where Pair dep_vars nondep_vars = foldMap split_dep_vars tys -- | Worker for 'splitDepVarsOfType'. This might output the same var -- in both sets, if it's used in both a type and a kind. -- See Note [TcDepVars determinism] split_dep_vars :: Type -> Pair DTyCoVarSet -- Pair kvs tvs split_dep_vars = go where go (TyVarTy tv) = Pair (tyCoVarsOfTypeDSet $ tyVarKind tv) (unitDVarSet tv) go (AppTy t1 t2) = go t1 `mappend` go t2 go (TyConApp _ tys) = foldMap go tys go (ForAllTy (Anon arg) res) = go arg `mappend` go res go (ForAllTy (Named tv _) ty) = let Pair kvs tvs = go ty in Pair (kvs `delDVarSet` tv `extendDVarSetList` tyCoVarsOfTypeList (tyVarKind tv)) (tvs `delDVarSet` tv) go (LitTy {}) = mempty go (CastTy ty co) = go ty `mappend` Pair (tyCoVarsOfCoDSet co) emptyDVarSet go (CoercionTy co) = Pair (tyCoVarsOfCoDSet co) emptyDVarSet isTouchableOrFmv ctxt_tclvl tv = ASSERT2( isTcTyVar tv, ppr tv ) case tcTyVarDetails tv of MetaTv { mtv_tclvl = tv_tclvl, mtv_info = info } -> ASSERT2( checkTcLevelInvariant ctxt_tclvl tv_tclvl, ppr tv $$ ppr tv_tclvl $$ ppr ctxt_tclvl ) case info of FlatMetaTv -> True _ -> tv_tclvl `sameDepthAs` ctxt_tclvl _ -> False isTouchableMetaTyVar :: TcLevel -> TcTyVar -> Bool isTouchableMetaTyVar ctxt_tclvl tv | isTyVar tv = ASSERT2( isTcTyVar tv, ppr tv ) case tcTyVarDetails tv of MetaTv { mtv_tclvl = tv_tclvl } -> ASSERT2( checkTcLevelInvariant ctxt_tclvl tv_tclvl, ppr tv $$ ppr tv_tclvl $$ ppr ctxt_tclvl ) tv_tclvl `sameDepthAs` ctxt_tclvl _ -> False | otherwise = False isFloatedTouchableMetaTyVar :: TcLevel -> TcTyVar -> Bool isFloatedTouchableMetaTyVar ctxt_tclvl tv | isTyVar tv = ASSERT2( isTcTyVar tv, ppr tv ) case tcTyVarDetails tv of MetaTv { mtv_tclvl = tv_tclvl } -> tv_tclvl `strictlyDeeperThan` ctxt_tclvl _ -> False | otherwise = False isImmutableTyVar :: TyVar -> Bool isImmutableTyVar tv | isTcTyVar tv = isSkolemTyVar tv | otherwise = True 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 SigTv | isTyVar tv = ASSERT2( isTcTyVar tv, ppr tv ) case tcTyVarDetails tv of MetaTv { mtv_info = SigTv } -> False _ -> True | otherwise = True isFmvTyVar tv = ASSERT2( isTcTyVar tv, ppr tv ) case tcTyVarDetails tv of MetaTv { mtv_info = FlatMetaTv } -> True _ -> False -- | True of both given and wanted flatten-skolems (fak and usk) isFlattenTyVar tv = ASSERT2( isTcTyVar tv, ppr tv ) case tcTyVarDetails tv of FlatSkol {} -> True MetaTv { mtv_info = FlatMetaTv } -> True _ -> False -- | True of FlatSkol skolems only isFskTyVar tv = ASSERT2( isTcTyVar tv, ppr tv ) case tcTyVarDetails tv of FlatSkol {} -> True _ -> False isSkolemTyVar tv = ASSERT2( isTcTyVar tv, ppr tv ) case tcTyVarDetails tv of MetaTv {} -> False _other -> True isOverlappableTyVar tv | isTyVar tv = ASSERT2( isTcTyVar tv, ppr tv ) case tcTyVarDetails tv of SkolemTv overlappable -> overlappable _ -> False | otherwise = False isMetaTyVar tv | isTyVar tv = ASSERT2( isTcTyVar tv, ppr tv ) 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 -- RtClosureInspect.zonkRTTIType. These are "ambiguous" in -- the sense that they stand for an as-yet-unknown type isAmbiguousTyVar tv | isTyVar tv = 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) 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 setMetaTyVarTcLevel :: TcTyVar -> TcLevel -> TcTyVar setMetaTyVarTcLevel tv tclvl = case tcTyVarDetails tv of details@(MetaTv {}) -> setTcTyVarDetails tv (details { mtv_tclvl = tclvl }) _ -> pprPanic "metaTyVarTcLevel" (ppr tv) isSigTyVar :: Var -> Bool isSigTyVar tv = case tcTyVarDetails tv of MetaTv { mtv_info = SigTv } -> True _ -> False metaTvRef :: TyVar -> IORef MetaDetails metaTvRef tv = case tcTyVarDetails tv of MetaTv { mtv_ref = ref } -> ref _ -> pprPanic "metaTvRef" (ppr tv) isFlexi, isIndirect :: MetaDetails -> Bool isFlexi Flexi = True isFlexi _ = False isIndirect (Indirect _) = True isIndirect _ = False isRuntimeUnkSkol :: TyVar -> Bool -- Called only in TcErrors; see Note [Runtime skolems] there isRuntimeUnkSkol x | isTcTyVar x, RuntimeUnk <- tcTyVarDetails x = True | otherwise = False {- ************************************************************************ * * \subsection{Tau, sigma and rho} * * ************************************************************************ -} mkSigmaTy :: [TyBinder] -> [PredType] -> Type -> Type mkSigmaTy bndrs theta tau = mkForAllTys bndrs (mkPhiTy theta tau) mkInvSigmaTy :: [TyVar] -> [PredType] -> Type -> Type mkInvSigmaTy tyvars = mkSigmaTy (mkNamedBinders Invisible tyvars) -- | 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 = mkSigmaTy (mkNamedBinders Specified tyvars) mkPhiTy :: [PredType] -> Type -> Type mkPhiTy = mkFunTys -- @isTauTy@ tests if a type is "simple".. isTauTy :: Type -> Bool isTauTy ty | Just ty' <- coreView ty = isTauTy ty' isTauTy (TyVarTy _) = True isTauTy (LitTy {}) = True isTauTy (TyConApp tc tys) = all isTauTy tys && isTauTyCon tc isTauTy (AppTy a b) = isTauTy a && isTauTy b isTauTy (ForAllTy (Anon a) b) = isTauTy a && isTauTy b isTauTy (ForAllTy {}) = False isTauTy (CastTy _ _) = False isTauTy (CoercionTy _) = False isTauTyCon :: TyCon -> Bool -- Returns False for type synonyms whose expansion is a polytype isTauTyCon tc | Just (_, rhs) <- synTyConDefn_maybe tc = isTauTy rhs | otherwise = True --------------- 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 (ForAllTy (Anon _) _) = getOccName funTyCon getDFunTyKey (ForAllTy (Named {}) 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 --------------- mkNakedTyConApp :: TyCon -> [Type] -> Type -- Builds a TyConApp -- * without being strict in TyCon, -- * without satisfying the invariants of TyConApp -- A subsequent zonking will establish the invariants -- See Note [Type-checking inside the knot] in TcHsType mkNakedTyConApp tc tys = TyConApp tc tys mkNakedAppTys :: Type -> [Type] -> Type -- See Note [Type-checking inside the knot] in TcHsType mkNakedAppTys ty1 [] = ty1 mkNakedAppTys (TyConApp tc tys1) tys2 = mkNakedTyConApp tc (tys1 ++ tys2) mkNakedAppTys ty1 tys2 = foldl AppTy ty1 tys2 mkNakedAppTy :: Type -> Type -> Type -- See Note [Type-checking inside the knot] in TcHsType mkNakedAppTy ty1 ty2 = mkNakedAppTys ty1 [ty2] mkNakedCastTy :: Type -> Coercion -> Type mkNakedCastTy = CastTy {- ************************************************************************ * * \subsection{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 = splitPiTys tcSplitForAllTy_maybe :: Type -> Maybe (TyBinder, Type) tcSplitForAllTy_maybe ty | Just ty' <- coreView ty = tcSplitForAllTy_maybe ty' tcSplitForAllTy_maybe (ForAllTy tv ty) = Just (tv, ty) tcSplitForAllTy_maybe _ = Nothing -- | Like 'tcSplitPiTys', but splits off only named binders, returning -- just the tycovars. tcSplitForAllTys :: Type -> ([TyVar], Type) tcSplitForAllTys = splitForAllTys -- | Like 'tcSplitForAllTys', but splits off only named binders. tcSplitNamedPiTys :: Type -> ([TyBinder], Type) tcSplitNamedPiTys = splitNamedPiTys -- | Is this a ForAllTy with a named binder? tcIsForAllTy :: Type -> Bool tcIsForAllTy ty | Just ty' <- coreView ty = tcIsForAllTy ty' tcIsForAllTy (ForAllTy (Named {}) _) = True tcIsForAllTy _ = False tcSplitPredFunTy_maybe :: Type -> Maybe (PredType, Type) -- Split off the first predicate argument from a type tcSplitPredFunTy_maybe ty | Just ty' <- coreView ty = tcSplitPredFunTy_maybe ty' tcSplitPredFunTy_maybe (ForAllTy (Anon arg) res) | isPredTy arg = 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) ----------------------- tcDeepSplitSigmaTy_maybe :: TcSigmaType -> Maybe ([TcType], [TyVar], ThetaType, TcSigmaType) -- Looks for a *non-trivial* quantified type, under zero or more function arrows -- By "non-trivial" we mean either tyvars or constraints are non-empty tcDeepSplitSigmaTy_maybe ty | Just (arg_ty, res_ty) <- tcSplitFunTy_maybe ty , Just (arg_tys, tvs, theta, rho) <- tcDeepSplitSigmaTy_maybe res_ty = Just (arg_ty:arg_tys, tvs, theta, rho) | (tvs, theta, rho) <- tcSplitSigmaTy ty , not (null tvs && null theta) = Just ([], tvs, theta, rho) | otherwise = Nothing ----------------------- tcTyConAppTyCon :: Type -> TyCon tcTyConAppTyCon ty = case tcSplitTyConApp_maybe ty of Just (tc, _) -> tc Nothing -> pprPanic "tcTyConAppTyCon" (pprType ty) 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) tcSplitTyConApp_maybe :: Type -> Maybe (TyCon, [Type]) tcSplitTyConApp_maybe ty | Just ty' <- coreView ty = tcSplitTyConApp_maybe ty' tcSplitTyConApp_maybe ty = tcRepSplitTyConApp_maybe ty tcRepSplitTyConApp_maybe :: Type -> Maybe (TyCon, [Type]) tcRepSplitTyConApp_maybe (TyConApp tc tys) = Just (tc, tys) tcRepSplitTyConApp_maybe (ForAllTy (Anon arg) res) = Just (funTyCon, [arg,res]) tcRepSplitTyConApp_maybe _ = Nothing ----------------------- tcSplitFunTys :: Type -> ([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 (Type, Type) tcSplitFunTy_maybe ty | Just ty' <- coreView ty = tcSplitFunTy_maybe ty' tcSplitFunTy_maybe (ForAllTy (Anon arg) res) | not (isPredTy arg) = Just (arg, res) tcSplitFunTy_maybe _ = Nothing -- Note the typeKind 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 :: TcRhoType -> Arity -- N: Number of desired args -> ([TcSigmaType], -- Arg types (N or fewer) TcSigmaType) -- The rest of the type tcSplitFunTysN ty n_args | n_args == 0 = ([], ty) | Just (arg,res) <- tcSplitFunTy_maybe ty = case tcSplitFunTysN res (n_args - 1) of (args, res) -> (arg:args, res) | otherwise = ([], ty) tcSplitFunTy :: Type -> (Type, Type) tcSplitFunTy ty = expectJust "tcSplitFunTy" (tcSplitFunTy_maybe ty) tcFunArgTy :: Type -> Type tcFunArgTy ty = fst (tcSplitFunTy ty) tcFunResultTy :: Type -> Type tcFunResultTy ty = snd (tcSplitFunTy ty) ----------------------- tcSplitAppTy_maybe :: Type -> Maybe (Type, Type) tcSplitAppTy_maybe ty | Just ty' <- coreView 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) ----------------------- tcGetTyVar_maybe :: Type -> Maybe TyVar tcGetTyVar_maybe ty | Just ty' <- coreView ty = tcGetTyVar_maybe ty' tcGetTyVar_maybe (TyVarTy tv) = Just tv tcGetTyVar_maybe _ = Nothing tcGetTyVar :: String -> Type -> TyVar tcGetTyVar msg ty = expectJust msg (tcGetTyVar_maybe ty) tcIsTyVarTy :: Type -> Bool tcIsTyVarTy ty | Just ty' <- coreView 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, theta, clas, tys) }}} tcSplitDFunHead :: Type -> (Class, [Type]) tcSplitDFunHead = getClassPredTys tcEqKind :: TcKind -> TcKind -> Bool tcEqKind = tcEqType tcEqType :: TcType -> TcType -> Bool -- tcEqType is a proper implements the same Note [Non-trivial definitional -- equality] (in TyCoRep) as `eqType`, but Type.eqType believes (* == -- Constraint), and that is NOT what we want in the type checker! tcEqType ty1 ty2 = isNothing (tc_eq_type coreView ki1 ki2) && isNothing (tc_eq_type coreView ty1 ty2) where ki1 = typeKind ty1 ki2 = typeKind 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 = isNothing $ tc_eq_type coreView ty1 ty2 -- | Like 'tcEqType', but returns information about whether the difference -- is visible in the case of a mismatch. A return of Nothing means the types -- are 'tcEqType'. tcEqTypeVis :: TcType -> TcType -> Maybe VisibilityFlag tcEqTypeVis ty1 ty2 = tc_eq_type coreView ty1 ty2 invis (tc_eq_type coreView ki1 ki2) where ki1 = typeKind ty1 ki2 = typeKind ty2 -- convert Just Visible to Just Invisible invis :: Maybe VisibilityFlag -> Maybe VisibilityFlag invis = fmap (const Invisible) () :: Maybe VisibilityFlag -> Maybe VisibilityFlag -> Maybe VisibilityFlag Nothing x = x Just Visible _ = Just Visible Just _inv Just Visible = Just Visible Just inv _ = Just inv infixr 3 -- | Real worker for 'tcEqType'. No kind check! tc_eq_type :: (TcType -> Maybe TcType) -- ^ @coreView@, if you want unwrapping -> Type -> Type -> Maybe VisibilityFlag tc_eq_type view_fun orig_ty1 orig_ty2 = go Visible orig_env orig_ty1 orig_ty2 where go vis env t1 t2 | Just t1' <- view_fun t1 = go vis env t1' t2 go vis env t1 t2 | Just t2' <- view_fun t2 = go vis env t1 t2' go vis env (TyVarTy tv1) (TyVarTy tv2) = check vis $ rnOccL env tv1 == rnOccR env tv2 go vis _ (LitTy lit1) (LitTy lit2) = check vis $ lit1 == lit2 go vis env (ForAllTy (Named tv1 vis1) ty1) (ForAllTy (Named tv2 vis2) ty2) = go vis1 env (tyVarKind tv1) (tyVarKind tv2) go vis (rnBndr2 env tv1 tv2) ty1 ty2 check vis (vis1 == vis2) go vis env (ForAllTy (Anon arg1) res1) (ForAllTy (Anon arg2) res2) = go vis env arg1 arg2 go vis env res1 res2 -- See Note [Equality on AppTys] in Type go vis env (AppTy s1 t1) ty2 | Just (s2, t2) <- tcRepSplitAppTy_maybe ty2 = go vis env s1 s2 go vis env t1 t2 go vis env ty1 (AppTy s2 t2) | Just (s1, t1) <- tcRepSplitAppTy_maybe ty1 = go vis env s1 s2 go vis env t1 t2 go vis env (TyConApp tc1 ts1) (TyConApp tc2 ts2) = check vis (tc1 == tc2) gos (tc_vis vis tc1) env ts1 ts2 go vis env (CastTy t1 _) t2 = go vis env t1 t2 go vis env t1 (CastTy t2 _) = go vis env t1 t2 go _ _ (CoercionTy {}) (CoercionTy {}) = Nothing go vis _ _ _ = Just vis gos _ _ [] [] = Nothing gos (v:vs) env (t1:ts1) (t2:ts2) = go v env t1 t2 gos vs env ts1 ts2 gos (v:_) _ _ _ = Just v gos _ _ _ _ = panic "tc_eq_type" tc_vis :: VisibilityFlag -> TyCon -> [VisibilityFlag] tc_vis Visible tc = viss ++ repeat Visible -- the repeat Visible is necessary because tycons can legitimately -- be oversaturated where bndrs = tyConBinders tc viss = map binderVisibility bndrs tc_vis vis _ = repeat vis -- if we're not in a visible context, our args -- aren't either check :: VisibilityFlag -> Bool -> Maybe VisibilityFlag check _ True = Nothing check vis False = Just vis orig_env = mkRnEnv2 $ mkInScopeSet $ tyCoVarsOfTypes [orig_ty1, orig_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 = isNothing $ tc_eq_type (const Nothing) ty1 ty2 {- Note [Occurs check expansion] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ (occurCheckExpand tv xi) expands synonyms in xi just enough to get rid of occurrences of tv outside type function arguments, if that is possible; otherwise, it returns Nothing. For example, suppose we have type F a b = [a] Then occurCheckExpand b (F Int b) = Just [Int] but occurCheckExpand a (F a Int) = Nothing We don't promise to do the absolute minimum amount of expanding necessary, but we try not to do expansions we don't need to. We prefer doing inner expansions first. For example, type F a b = (a, Int, a, [a]) type G b = Char We have occurCheckExpand b (F (G b)) = F Char even though we could also expand F to get rid of b. The two variants of the function are to support TcUnify.checkTauTvUpdate, which wants to prevent unification with type families. For more on this point, see Note [Prevent unification with type families] in TcUnify. See also Note [occurCheckExpand] in TcCanonical -} data OccCheckResult a = OC_OK a | OC_Forall | OC_Occurs instance Functor OccCheckResult where fmap = liftM instance Applicative OccCheckResult where pure = OC_OK (<*>) = ap instance Monad OccCheckResult where return = pure OC_OK x >>= k = k x OC_Forall >>= _ = OC_Forall OC_Occurs >>= _ = OC_Occurs occurCheckExpand :: DynFlags -> TcTyVar -> Type -> OccCheckResult Type -- See Note [Occurs check expansion] -- Check whether -- a) the given variable occurs in the given type. -- b) there is a forall in the type (unless we have -XImpredicativeTypes) -- -- We may have needed to do some type synonym unfolding in order to -- get rid of the variable (or forall), so we also return the unfolded -- version of the type, which is guaranteed to be syntactically free -- of the given type variable. If the type is already syntactically -- free of the variable, then the same type is returned. -- -- NB: in the past we also rejected a SigTv matched with a non-tyvar -- But it is wrong to reject that for Givens; -- and SigTv is in any case handled separately by -- - TcUnify.checkTauTvUpdate (on-the-fly unifier) -- - TcInteract.canSolveByUnification (main constraint solver) occurCheckExpand dflags tv ty | fast_check ty = return ty | otherwise = go emptyVarEnv ty where details = tcTyVarDetails tv impredicative = canUnifyWithPolyType dflags details -- True => fine fast_check (LitTy {}) = True fast_check (TyVarTy tv') = tv /= tv' && fast_check (tyVarKind tv') fast_check (TyConApp tc tys) = all fast_check tys && (isTauTyCon tc || impredicative) fast_check (ForAllTy (Anon a) r) = fast_check a && fast_check r fast_check (AppTy fun arg) = fast_check fun && fast_check arg fast_check (ForAllTy (Named tv' _) ty) = impredicative && fast_check (tyVarKind tv') && (tv == tv' || fast_check ty) fast_check (CastTy ty co) = fast_check ty && fast_check_co co fast_check (CoercionTy co) = fast_check_co co -- we really are only doing an occurs check here; no bother about -- impredicativity in coercions, as they're inferred fast_check_co co = not (tv `elemVarSet` tyCoVarsOfCo co) go :: VarEnv TyVar -- carries mappings necessary because of kind expansion -> Type -> OccCheckResult Type go env (TyVarTy tv') | tv == tv' = OC_Occurs | Just tv'' <- lookupVarEnv env tv' = return (mkTyVarTy tv'') | otherwise = do { k' <- go env (tyVarKind tv') ; return (mkTyVarTy $ setTyVarKind tv' k') } go _ ty@(LitTy {}) = return ty go env (AppTy ty1 ty2) = do { ty1' <- go env ty1 ; ty2' <- go env ty2 ; return (mkAppTy ty1' ty2') } go env (ForAllTy (Anon ty1) ty2) = do { ty1' <- go env ty1 ; ty2' <- go env ty2 ; return (mkFunTy ty1' ty2') } go env ty@(ForAllTy (Named tv' vis) body_ty) | not impredicative = OC_Forall | tv == tv' = return ty | otherwise = do { ki' <- go env ki ; let tv'' = setTyVarKind tv' ki' env' = extendVarEnv env tv' tv'' ; body' <- go env' body_ty ; return (ForAllTy (Named tv'' vis) body') } where ki = tyVarKind tv' -- For a type constructor application, first try expanding away the -- offending variable from the arguments. If that doesn't work, next -- see if the type constructor is a type synonym, and if so, expand -- it and try again. go env ty@(TyConApp tc tys) = case do { tys <- mapM (go env) tys ; return (mkTyConApp tc tys) } of OC_OK ty | impredicative || isTauTyCon tc -> return ty -- First try to eliminate the tyvar from the args | otherwise -> OC_Forall -- A type synonym with a forall on the RHS bad | Just ty' <- coreView ty -> go env ty' | otherwise -> bad -- Failing that, try to expand a synonym go env (CastTy ty co) = do { ty' <- go env ty ; co' <- go_co env co ; return (mkCastTy ty' co') } go env (CoercionTy co) = do { co' <- go_co env co ; return (mkCoercionTy co') } go_co env (Refl r ty) = do { ty' <- go env ty ; return (mkReflCo r ty') } -- Note: Coercions do not contain type synonyms go_co env (TyConAppCo r tc args) = do { args' <- mapM (go_co env) args ; return (mkTyConAppCo r tc args') } go_co env (AppCo co arg) = do { co' <- go_co env co ; arg' <- go_co env arg ; return (mkAppCo co' arg') } go_co env co@(ForAllCo tv' kind_co body_co) | not impredicative = OC_Forall | tv == tv' = return co | otherwise = do { kind_co' <- go_co env kind_co ; let tv'' = setTyVarKind tv' $ pFst (coercionKind kind_co') env' = extendVarEnv env tv' tv'' ; body' <- go_co env' body_co ; return (ForAllCo tv'' kind_co' body') } go_co env (CoVarCo c) = do { k' <- go env (varType c) ; return (mkCoVarCo (setVarType c k')) } go_co env (AxiomInstCo ax ind args) = do { args' <- mapM (go_co env) args ; return (mkAxiomInstCo ax ind args') } go_co env (UnivCo p r ty1 ty2) = do { p' <- go_prov env p ; ty1' <- go env ty1 ; ty2' <- go env ty2 ; return (mkUnivCo p' r ty1' ty2') } go_co env (SymCo co) = do { co' <- go_co env co ; return (mkSymCo co') } go_co env (TransCo co1 co2) = do { co1' <- go_co env co1 ; co2' <- go_co env co2 ; return (mkTransCo co1' co2') } go_co env (NthCo n co) = do { co' <- go_co env co ; return (mkNthCo n co') } go_co env (LRCo lr co) = do { co' <- go_co env co ; return (mkLRCo lr co') } go_co env (InstCo co arg) = do { co' <- go_co env co ; arg' <- go_co env arg ; return (mkInstCo co' arg') } go_co env (CoherenceCo co1 co2) = do { co1' <- go_co env co1 ; co2' <- go_co env co2 ; return (mkCoherenceCo co1' co2') } go_co env (KindCo co) = do { co' <- go_co env co ; return (mkKindCo co') } go_co env (SubCo co) = do { co' <- go_co env co ; return (mkSubCo co') } go_co env (AxiomRuleCo ax cs) = do { cs' <- mapM (go_co env) cs ; return (mkAxiomRuleCo ax cs') } go_prov _ UnsafeCoerceProv = return UnsafeCoerceProv go_prov env (PhantomProv co) = PhantomProv <$> go_co env co go_prov env (ProofIrrelProv co) = ProofIrrelProv <$> go_co env co go_prov _ p@(PluginProv _) = return p go_prov _ p@(HoleProv _) = return p canUnifyWithPolyType :: DynFlags -> TcTyVarDetails -> Bool canUnifyWithPolyType dflags details = case details of MetaTv { mtv_info = SigTv } -> False MetaTv { mtv_info = TauTv } -> xopt LangExt.ImpredicativeTypes dflags _other -> True -- We can have non-meta tyvars in given constraints {- Note [Expanding superclasses] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ When we expand superclasses, we use the following algorithm: expand( so_far, pred ) returns the transitive superclasses of pred, not including pred itself 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. * 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. Somthing better would be cool. See also TcTyDecls.checkClassCycles. ************************************************************************ * * \subsection{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 TcValidity because it is -- called from TcSimplify, which itself is imported by TcValidity 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_maybe :: EvVar -> Maybe PredType evVarPred_maybe v = if isPredTy ty then Just ty else Nothing where ty = varType v evVarPred :: EvVar -> PredType evVarPred var | debugIsOn = case evVarPred_maybe var of Just pred -> pred Nothing -> pprPanic "tcEvVarPred" (ppr var <+> ppr (varType var)) | otherwise = varType var ------------------ -- | 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 -- Context from PartialTypeSignatures -> TcThetaType -- Proposed constraints to quantify -> TcThetaType -- A subset that we can actually quantify -- This function decides whether a particular constraint shoudl be -- quantified over, given the type variables that are being quantified pickQuantifiablePreds qtvs annotated_theta theta = let flex_ctxt = True in -- Quantify over non-tyvar constraints, even without -- -XFlexibleContexts: see Trac #10608, #10351 -- flex_ctxt <- xoptM Opt_FlexibleContexts filter (pick_me flex_ctxt) theta where pick_me flex_ctxt pred = case classifyPredType pred of ClassPred cls tys | Just str <- isCallStackPred pred -- NEVER infer a CallStack constraint, unless we were -- given one in a partial type signatures. -- 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] -> str `elem` givenStks | isIPClass cls -> True -- See note [Inheriting implicit parameters] | otherwise -> pick_cls_pred flex_ctxt cls tys EqPred ReprEq ty1 ty2 -> pick_cls_pred flex_ctxt coercibleClass [ty1, ty2] -- representational equality is like a class constraint EqPred NomEq ty1 ty2 -> quant_fun ty1 || quant_fun ty2 IrredPred ty -> tyCoVarsOfType ty `intersectsVarSet` qtvs givenStks = [ str | (str, ty) <- mapMaybe isIPPred_maybe annotated_theta , isCallStackTy ty ] 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 Trac #10351. -- See Note [Quantifying over equality constraints] quant_fun ty = case tcSplitTyConApp_maybe ty of Just (tc, tys) | isTypeFamilyTyCon tc -> tyCoVarsOfTypes tys `intersectsVarSet` qtvs _ -> False -- Superclasses type PredWithSCs = (PredType, [PredType]) mkMinimalBySCs :: [PredType] -> [PredType] -- Remove predicates that can be deduced from others by superclasses -- Result is a subset of the input mkMinimalBySCs ptys = go preds_with_scs [] where preds_with_scs :: [PredWithSCs] preds_with_scs = [ (pred, transSuperClasses pred) | pred <- ptys ] go :: [PredWithSCs] -- Work list -> [PredWithSCs] -- Accumulating result -> [PredType] go [] min_preds = map fst min_preds go (work_item@(p,_) : 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] -> Bool in_cloud p ps = or [ p `eqType` 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? {- 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. ************************************************************************ * * \subsection{Predicates} * * ************************************************************************ -} 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' <- coreView ty = isSigmaTy ty' isSigmaTy (ForAllTy (Named {}) _) = True isSigmaTy (ForAllTy (Anon a) _) = isPredTy a isSigmaTy _ = False isRhoTy :: TcType -> Bool -- True of TcRhoTypes; see Note [TcRhoType] isRhoTy ty | Just ty' <- coreView ty = isRhoTy ty' isRhoTy (ForAllTy (Named {}) _) = False isRhoTy (ForAllTy (Anon a) r) = not (isPredTy a) && isRhoTy r 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' <- coreView ty = isOverloadedTy ty' isOverloadedTy (ForAllTy (Named {}) ty) = isOverloadedTy ty isOverloadedTy (ForAllTy (Anon a) _) = isPredTy a isOverloadedTy _ = False isFloatTy, isDoubleTy, isIntegerTy, isIntTy, isWordTy, isBoolTy, isUnitTy, isCharTy, isAnyTy :: Type -> Bool isFloatTy = is_tc floatTyConKey isDoubleTy = is_tc doubleTyConKey isIntegerTy = is_tc integerTyConKey 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 :: PredType -> Maybe FastString isCallStackPred pred | Just (str, ty) <- isIPPred_maybe pred , isCallStackTy ty = Just str | 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 in the given type outside of any -- non-newtypes? Assume we're looking for @a@. Says "yes" for -- @a@, @N a@, @b a@, @a b@, @b (N a)@. Says "no" for -- @[a]@, @Maybe a@, @T a@, where @N@ is a newtype and @T@ is a datatype. isTyVarExposed :: TcTyVar -> TcType -> Bool isTyVarExposed tv (TyVarTy tv') = tv == tv' isTyVarExposed tv (TyConApp tc tys) | isNewTyCon tc = any (isTyVarExposed tv) tys | otherwise = False isTyVarExposed _ (LitTy {}) = False isTyVarExposed tv (AppTy fun arg) = isTyVarExposed tv fun || isTyVarExposed tv arg isTyVarExposed _ (ForAllTy {}) = False isTyVarExposed tv (CastTy ty _) = isTyVarExposed tv ty isTyVarExposed _ (CoercionTy {}) = False -- | Does the given tyvar appear under a type generative w.r.t. -- representational equality? See Note [Occurs check error] in -- TcCanonical for the motivation for this function. isTyVarUnderDatatype :: TcTyVar -> TcType -> Bool isTyVarUnderDatatype tv = go False where go under_dt ty | Just ty' <- coreView ty = go under_dt ty' go under_dt (TyVarTy tv') = under_dt && (tv == tv') go under_dt (TyConApp tc tys) = let under_dt' = under_dt || isGenerativeTyCon tc Representational in any (go under_dt') tys go _ (LitTy {}) = False go _ (ForAllTy (Anon arg) res) = go True arg || go True res go under_dt (AppTy fun arg) = go under_dt fun || go under_dt arg go under_dt (ForAllTy (Named tv' _) inner_ty) | tv' == tv = False | otherwise = go under_dt inner_ty go under_dt (CastTy ty _) = go under_dt ty go _ (CoercionTy {}) = False isRigidTy :: TcType -> Bool isRigidTy ty | Just (tc,_) <- tcSplitTyConApp_maybe ty = isGenerativeTyCon tc Nominal | Just {} <- tcSplitAppTy_maybe ty = True | isForAllTy ty = True | otherwise = False isRigidEqPred :: TcLevel -> PredTree -> Bool -- ^ True of all Nominal equalities that are solidly insoluble -- This means all equalities *except* -- * Meta-tv non-SigTv on LHS -- * Meta-tv SigTv on LHS, tyvar on right isRigidEqPred tc_lvl (EqPred NomEq ty1 _) | Just tv1 <- tcGetTyVar_maybe ty1 = ASSERT2( isTcTyVar tv1, ppr tv1 ) not (isMetaTyVar tv1) || isTouchableMetaTyVar tc_lvl tv1 | otherwise -- LHS is not a tyvar = True isRigidEqPred _ _ = False -- Not an equality {- ************************************************************************ * * \subsection{Transformation of Types to TcTypes} * * ************************************************************************ -} toTcType :: Type -> TcType -- The constraint solver expects EvVars to have TcType, in which the -- free type variables are TcTyVars. So we convert from Type to TcType here -- A bit tiresome; but one day I expect the two types to be entirely separate -- in which case we'll definitely need to do this toTcType = runIdentity . to_tc_type emptyVarSet toTcTypeBag :: Bag EvVar -> Bag EvVar -- All TyVars are transformed to TcTyVars toTcTypeBag evvars = mapBag (\tv -> setTyVarKind tv (toTcType (tyVarKind tv))) evvars to_tc_mapper :: TyCoMapper VarSet Identity to_tc_mapper = TyCoMapper { tcm_smart = False -- more efficient not to use smart ctors , tcm_tyvar = tyvar , tcm_covar = covar , tcm_hole = hole , tcm_tybinder = tybinder } where tyvar :: VarSet -> TyVar -> Identity Type tyvar ftvs tv | Just var <- lookupVarSet ftvs tv = return $ TyVarTy var | isTcTyVar tv = TyVarTy <$> updateTyVarKindM (to_tc_type ftvs) tv | otherwise = do { kind' <- to_tc_type ftvs (tyVarKind tv) ; return $ TyVarTy $ mkTcTyVar (tyVarName tv) kind' vanillaSkolemTv } covar :: VarSet -> CoVar -> Identity Coercion covar ftvs cv | Just var <- lookupVarSet ftvs cv = return $ CoVarCo var | otherwise = CoVarCo <$> updateVarTypeM (to_tc_type ftvs) cv hole :: VarSet -> CoercionHole -> Role -> Type -> Type -> Identity Coercion hole ftvs h r t1 t2 = mkHoleCo h r <$> to_tc_type ftvs t1 <*> to_tc_type ftvs t2 tybinder :: VarSet -> TyVar -> VisibilityFlag -> Identity (VarSet, TyVar) tybinder ftvs tv _vis = do { kind' <- to_tc_type ftvs (tyVarKind tv) ; let tv' = mkTcTyVar (tyVarName tv) kind' vanillaSkolemTv ; return (ftvs `extendVarSet` tv', tv') } to_tc_type :: VarSet -> Type -> Identity TcType to_tc_type = mapType to_tc_mapper {- ************************************************************************ * * \subsection{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. -} {- ************************************************************************ * * \subsection[TysWiredIn-ext-type]{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, -- 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) , case tyConPrimRep tc of -- Note [Marshalling VoidRep] VoidRep -> False _ -> True = 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 here since -- currently they're of the wrong kind to use in function args anyway. legalFIPrimArgTyCon dflags tc | isUnliftedTyCon tc , not (isUnboxedTupleTyCon 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 result types '... -> (# , , #)' legalFIPrimResultTyCon dflags tc | isUnliftedTyCon tc , (isUnboxedTupleTyCon tc || case tyConPrimRep tc of -- Note [Marshalling VoidRep] VoidRep -> False _ -> True) = 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 VoidRep] ~~~~~~~~~~~~~~~~~~~~~~~~~~ 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 Trac #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 Trac #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 <- coreView 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 go (LitTy {}) = 1 go (ForAllTy (Anon arg) res) = go arg + go res + 1 go (AppTy fun arg) = go fun + go arg go (ForAllTy (Named tv vis) ty) | Visible <- 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)