{- (c) The University of Glasgow 2006 (c) The GRASP/AQUA Project, Glasgow University, 1992-1998 The @TyCon@ datatype -} {-# LANGUAGE CPP, FlexibleInstances #-} module TyCon( -- * Main TyCon data types TyCon, AlgTyConRhs(..), visibleDataCons, AlgTyConFlav(..), isNoParent, FamTyConFlav(..), Role(..), Injectivity(..), RuntimeRepInfo(..), TyConFlavour(..), -- * TyConBinder TyConBinder, TyConBndrVis(..), mkNamedTyConBinder, mkNamedTyConBinders, mkAnonTyConBinder, mkAnonTyConBinders, tyConBinderArgFlag, tyConBndrVisArgFlag, isNamedTyConBinder, isVisibleTyConBinder, isInvisibleTyConBinder, -- ** Field labels tyConFieldLabels, lookupTyConFieldLabel, -- ** Constructing TyCons mkAlgTyCon, mkClassTyCon, mkFunTyCon, mkPrimTyCon, mkKindTyCon, mkLiftedPrimTyCon, mkTupleTyCon, mkSumTyCon, mkDataTyConRhs, mkSynonymTyCon, mkFamilyTyCon, mkPromotedDataCon, mkTcTyCon, -- ** Predicates on TyCons isAlgTyCon, isVanillaAlgTyCon, isClassTyCon, isFamInstTyCon, isFunTyCon, isPrimTyCon, isTupleTyCon, isUnboxedTupleTyCon, isBoxedTupleTyCon, isUnboxedSumTyCon, isPromotedTupleTyCon, isTypeSynonymTyCon, mightBeUnsaturatedTyCon, isPromotedDataCon, isPromotedDataCon_maybe, isKindTyCon, isLiftedTypeKindTyConName, isTauTyCon, isFamFreeTyCon, isDataTyCon, isProductTyCon, isDataProductTyCon_maybe, isDataSumTyCon_maybe, isEnumerationTyCon, isNewTyCon, isAbstractTyCon, isFamilyTyCon, isOpenFamilyTyCon, isTypeFamilyTyCon, isDataFamilyTyCon, isOpenTypeFamilyTyCon, isClosedSynFamilyTyConWithAxiom_maybe, tyConInjectivityInfo, isBuiltInSynFamTyCon_maybe, isUnliftedTyCon, isGadtSyntaxTyCon, isInjectiveTyCon, isGenerativeTyCon, isGenInjAlgRhs, isTyConAssoc, tyConAssoc_maybe, isImplicitTyCon, isTyConWithSrcDataCons, isTcTyCon, isTcLevPoly, -- ** Extracting information out of TyCons tyConName, tyConSkolem, tyConKind, tyConUnique, tyConTyVars, tyConVisibleTyVars, tyConCType, tyConCType_maybe, tyConDataCons, tyConDataCons_maybe, tyConSingleDataCon_maybe, tyConSingleDataCon, tyConSingleAlgDataCon_maybe, tyConFamilySize, tyConStupidTheta, tyConArity, tyConRoles, tyConFlavour, tyConTuple_maybe, tyConClass_maybe, tyConATs, tyConFamInst_maybe, tyConFamInstSig_maybe, tyConFamilyCoercion_maybe, tyConFamilyResVar_maybe, synTyConDefn_maybe, synTyConRhs_maybe, famTyConFlav_maybe, famTcResVar, algTyConRhs, newTyConRhs, newTyConEtadArity, newTyConEtadRhs, unwrapNewTyCon_maybe, unwrapNewTyConEtad_maybe, newTyConDataCon_maybe, algTcFields, tyConRuntimeRepInfo, tyConBinders, tyConResKind, tyConTyVarBinders, tcTyConScopedTyVars, tcTyConUserTyVars, mkTyConTagMap, -- ** Manipulating TyCons expandSynTyCon_maybe, makeRecoveryTyCon, newTyConCo, newTyConCo_maybe, pprPromotionQuote, mkTyConKind, -- ** Predicated on TyConFlavours tcFlavourCanBeUnsaturated, tcFlavourIsOpen, -- * Runtime type representation TyConRepName, tyConRepName_maybe, mkPrelTyConRepName, tyConRepModOcc, -- * Primitive representations of Types PrimRep(..), PrimElemRep(..), isVoidRep, isGcPtrRep, primRepSizeB, primElemRepSizeB, primRepIsFloat, -- * Recursion breaking RecTcChecker, initRecTc, checkRecTc ) where #include "HsVersions.h" import GhcPrelude import {-# SOURCE #-} TyCoRep ( Kind, Type, PredType, pprType ) import {-# SOURCE #-} TysWiredIn ( runtimeRepTyCon, constraintKind , vecCountTyCon, vecElemTyCon, liftedTypeKind , mkFunKind, mkForAllKind ) import {-# SOURCE #-} DataCon ( DataCon, dataConExTyVars, dataConFieldLabels , dataConTyCon, dataConFullSig ) import Binary import Var import Class import BasicTypes import DynFlags import ForeignCall import Name import NameEnv import CoAxiom import PrelNames import Maybes import Outputable import FastStringEnv import FieldLabel import Constants import Util import Unique( tyConRepNameUnique, dataConTyRepNameUnique ) import UniqSet import Module import {-# SOURCE #-} DataCon import qualified Data.Data as Data {- ----------------------------------------------- Notes about type families ----------------------------------------------- Note [Type synonym families] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~ * Type synonym families, also known as "type functions", map directly onto the type functions in FC: type family F a :: * type instance F Int = Bool ..etc... * Reply "yes" to isTypeFamilyTyCon, and isFamilyTyCon * From the user's point of view (F Int) and Bool are simply equivalent types. * A Haskell 98 type synonym is a degenerate form of a type synonym family. * Type functions can't appear in the LHS of a type function: type instance F (F Int) = ... -- BAD! * Translation of type family decl: type family F a :: * translates to a FamilyTyCon 'F', whose FamTyConFlav is OpenSynFamilyTyCon type family G a :: * where G Int = Bool G Bool = Char G a = () translates to a FamilyTyCon 'G', whose FamTyConFlav is ClosedSynFamilyTyCon, with the appropriate CoAxiom representing the equations We also support injective type families -- see Note [Injective type families] Note [Data type families] ~~~~~~~~~~~~~~~~~~~~~~~~~ See also Note [Wrappers for data instance tycons] in MkId.hs * Data type families are declared thus data family T a :: * data instance T Int = T1 | T2 Bool Here T is the "family TyCon". * Reply "yes" to isDataFamilyTyCon, and isFamilyTyCon * The user does not see any "equivalent types" as he did with type synonym families. He just sees constructors with types T1 :: T Int T2 :: Bool -> T Int * Here's the FC version of the above declarations: data T a data R:TInt = T1 | T2 Bool axiom ax_ti : T Int ~R R:TInt Note that this is a *representational* coercion The R:TInt is the "representation TyCons". It has an AlgTyConFlav of DataFamInstTyCon T [Int] ax_ti * The axiom ax_ti may be eta-reduced; see Note [Eta reduction for data family axioms] in FamInstEnv * Data family instances may have a different arity than the data family. See Note [Arity of data families] in FamInstEnv * The data constructor T2 has a wrapper (which is what the source-level "T2" invokes): $WT2 :: Bool -> T Int $WT2 b = T2 b `cast` sym ax_ti * A data instance can declare a fully-fledged GADT: data instance T (a,b) where X1 :: T (Int,Bool) X2 :: a -> b -> T (a,b) Here's the FC version of the above declaration: data R:TPair a where X1 :: R:TPair Int Bool X2 :: a -> b -> R:TPair a b axiom ax_pr :: T (a,b) ~R R:TPair a b $WX1 :: forall a b. a -> b -> T (a,b) $WX1 a b (x::a) (y::b) = X2 a b x y `cast` sym (ax_pr a b) The R:TPair are the "representation TyCons". We have a bit of work to do, to unpick the result types of the data instance declaration for T (a,b), to get the result type in the representation; e.g. T (a,b) --> R:TPair a b The representation TyCon R:TList, has an AlgTyConFlav of DataFamInstTyCon T [(a,b)] ax_pr * Notice that T is NOT translated to a FC type function; it just becomes a "data type" with no constructors, which can be coerced inot into R:TInt, R:TPair by the axioms. These axioms axioms come into play when (and *only* when) you - use a data constructor - do pattern matching Rather like newtype, in fact As a result - T behaves just like a data type so far as decomposition is concerned - (T Int) is not implicitly converted to R:TInt during type inference. Indeed the latter type is unknown to the programmer. - There *is* an instance for (T Int) in the type-family instance environment, but it is only used for overlap checking - It's fine to have T in the LHS of a type function: type instance F (T a) = [a] It was this last point that confused me! The big thing is that you should not think of a data family T as a *type function* at all, not even an injective one! We can't allow even injective type functions on the LHS of a type function: type family injective G a :: * type instance F (G Int) = Bool is no good, even if G is injective, because consider type instance G Int = Bool type instance F Bool = Char So a data type family is not an injective type function. It's just a data type with some axioms that connect it to other data types. * The tyConTyVars of the representation tycon are the tyvars that the user wrote in the patterns. This is important in TcDeriv, where we bring these tyvars into scope before type-checking the deriving clause. This fact is arranged for in TcInstDecls.tcDataFamInstDecl. Note [Associated families and their parent class] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ *Associated* families are just like *non-associated* families, except that they have a famTcParent field of (Just cls), which identifies the parent class. However there is an important sharing relationship between * the tyConTyVars of the parent Class * the tyConTyvars of the associated TyCon class C a b where data T p a type F a q b Here the 'a' and 'b' are shared with the 'Class'; that is, they have the same Unique. This is important. In an instance declaration we expect * all the shared variables to be instantiated the same way * the non-shared variables of the associated type should not be instantiated at all instance C [x] (Tree y) where data T p [x] = T1 x | T2 p type F [x] q (Tree y) = (x,y,q) Note [TyCon Role signatures] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Every tycon has a role signature, assigning a role to each of the tyConTyVars (or of equal length to the tyConArity, if there are no tyConTyVars). An example demonstrates these best: say we have a tycon T, with parameters a at nominal, b at representational, and c at phantom. Then, to prove representational equality between T a1 b1 c1 and T a2 b2 c2, we need to have nominal equality between a1 and a2, representational equality between b1 and b2, and nothing in particular (i.e., phantom equality) between c1 and c2. This might happen, say, with the following declaration: data T a b c where MkT :: b -> T Int b c Data and class tycons have their roles inferred (see inferRoles in TcTyDecls), as do vanilla synonym tycons. Family tycons have all parameters at role N, though it is conceivable that we could relax this restriction. (->)'s and tuples' parameters are at role R. Each primitive tycon declares its roles; it's worth noting that (~#)'s parameters are at role N. Promoted data constructors' type arguments are at role R. All kind arguments are at role N. Note [Unboxed tuple RuntimeRep vars] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The contents of an unboxed tuple may have any representation. Accordingly, the kind of the unboxed tuple constructor is runtime-representation polymorphic. For example, (#,#) :: forall (q :: RuntimeRep) (r :: RuntimeRep). TYPE q -> TYPE r -> # These extra tyvars (v and w) cause some delicate processing around tuples, where we used to be able to assume that the tycon arity and the datacon arity were the same. Note [Injective type families] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ We allow injectivity annotations for type families (both open and closed): type family F (a :: k) (b :: k) = r | r -> a type family G a b = res | res -> a b where ... Injectivity information is stored in the `famTcInj` field of `FamilyTyCon`. `famTcInj` maybe stores a list of Bools, where each entry corresponds to a single element of `tyConTyVars` (both lists should have identical length). If no injectivity annotation was provided `famTcInj` is Nothing. From this follows an invariant that if `famTcInj` is a Just then at least one element in the list must be True. See also: * [Injectivity annotation] in HsDecls * [Renaming injectivity annotation] in RnSource * [Verifying injectivity annotation] in FamInstEnv * [Type inference for type families with injectivity] in TcInteract ************************************************************************ * * TyConBinder * * ************************************************************************ -} type TyConBinder = TyVarBndr TyVar TyConBndrVis -- See also Note [TyBinder] in TyCoRep data TyConBndrVis = NamedTCB ArgFlag | AnonTCB instance Outputable TyConBndrVis where ppr (NamedTCB flag) = text "NamedTCB" <+> ppr flag ppr AnonTCB = text "AnonTCB" mkAnonTyConBinder :: TyVar -> TyConBinder mkAnonTyConBinder tv = TvBndr tv AnonTCB mkAnonTyConBinders :: [TyVar] -> [TyConBinder] mkAnonTyConBinders tvs = map mkAnonTyConBinder tvs mkNamedTyConBinder :: ArgFlag -> TyVar -> TyConBinder -- The odd argument order supports currying mkNamedTyConBinder vis tv = TvBndr tv (NamedTCB vis) mkNamedTyConBinders :: ArgFlag -> [TyVar] -> [TyConBinder] -- The odd argument order supports currying mkNamedTyConBinders vis tvs = map (mkNamedTyConBinder vis) tvs tyConBinderArgFlag :: TyConBinder -> ArgFlag tyConBinderArgFlag (TvBndr _ vis) = tyConBndrVisArgFlag vis tyConBndrVisArgFlag :: TyConBndrVis -> ArgFlag tyConBndrVisArgFlag (NamedTCB vis) = vis tyConBndrVisArgFlag AnonTCB = Required isNamedTyConBinder :: TyConBinder -> Bool -- Identifies kind variables -- E.g. data T k (a:k) = blah -- Here 'k' is a NamedTCB, a variable used in the kind of other binders isNamedTyConBinder (TvBndr _ (NamedTCB {})) = True isNamedTyConBinder _ = False isVisibleTyConBinder :: TyVarBndr tv TyConBndrVis -> Bool -- Works for IfaceTyConBinder too isVisibleTyConBinder (TvBndr _ tcb_vis) = isVisibleTcbVis tcb_vis isVisibleTcbVis :: TyConBndrVis -> Bool isVisibleTcbVis (NamedTCB vis) = isVisibleArgFlag vis isVisibleTcbVis AnonTCB = True isInvisibleTyConBinder :: TyVarBndr tv TyConBndrVis -> Bool -- Works for IfaceTyConBinder too isInvisibleTyConBinder tcb = not (isVisibleTyConBinder tcb) mkTyConKind :: [TyConBinder] -> Kind -> Kind mkTyConKind bndrs res_kind = foldr mk res_kind bndrs where mk :: TyConBinder -> Kind -> Kind mk (TvBndr tv AnonTCB) k = mkFunKind (tyVarKind tv) k mk (TvBndr tv (NamedTCB vis)) k = mkForAllKind tv vis k tyConTyVarBinders :: [TyConBinder] -- From the TyCon -> [TyVarBinder] -- Suitable for the foralls of a term function -- See Note [Building TyVarBinders from TyConBinders] tyConTyVarBinders tc_bndrs = map mk_binder tc_bndrs where mk_binder (TvBndr tv tc_vis) = mkTyVarBinder vis tv where vis = case tc_vis of AnonTCB -> Specified NamedTCB Required -> Specified NamedTCB vis -> vis tyConVisibleTyVars :: TyCon -> [TyVar] tyConVisibleTyVars tc = [ tv | TvBndr tv vis <- tyConBinders tc , isVisibleTcbVis vis ] {- Note [Building TyVarBinders from TyConBinders] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ We sometimes need to build the quantified type of a value from the TyConBinders of a type or class. For that we need not TyConBinders but TyVarBinders (used in forall-type) E.g: * From data T a = MkT (Maybe a) we are going to make a data constructor with type MkT :: forall a. Maybe a -> T a See the TyVarBinders passed to buildDataCon * From class C a where { op :: a -> Maybe a } we are going to make a default method $dmop :: forall a. C a => a -> Maybe a See the TyVarBindres passed to mkSigmaTy in mkDefaultMethodType Both of these are user-callable. (NB: default methods are not callable directly by the user but rather via the code generated by 'deriving', which uses visible type application; see mkDefMethBind.) Since they are user-callable we must get their type-argument visibility information right; and that info is in the TyConBinders. Here is an example: data App a b = MkApp (a b) -- App :: forall {k}. (k->*) -> k -> * The TyCon has tyConTyBinders = [ Named (TvBndr (k :: *) Inferred), Anon (k->*), Anon k ] The TyConBinders for App line up with App's kind, given above. But the DataCon MkApp has the type MkApp :: forall {k} (a:k->*) (b:k). a b -> App k a b That is, its TyVarBinders should be dataConUnivTyVarBinders = [ TvBndr (k:*) Inferred , TvBndr (a:k->*) Specified , TvBndr (b:k) Specified ] So tyConTyVarBinders converts TyCon's TyConBinders into TyVarBinders: - variable names from the TyConBinders - but changing Anon/Required to Specified The last part about Required->Specified comes from this: data T k (a:k) b = MkT (a b) Here k is Required in T's kind, but we don't have Required binders in the TyBinders for a term (see Note [No Required TyBinder in terms] in TyCoRep), so we change it to Specified when making MkT's TyBinders -} {- Note [The binders/kind/arity fields of a TyCon] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ All TyCons have this group of fields tyConBinders :: [TyConBinder] tyConResKind :: Kind tyConTyVars :: [TyVar] -- Cached = binderVars tyConBinders tyConKind :: Kind -- Cached = mkTyConKind tyConBinders tyConResKind tyConArity :: Arity -- Cached = length tyConBinders They fit together like so: * tyConBinders gives the telescope of type variables on the LHS of the type declaration. For example: type App a (b :: k) = a b tyConBinders = [ TvBndr (k::*) (NamedTCB Inferred) , TvBndr (a:k->*) AnonTCB , TvBndr (b:k) AnonTCB ] Note that that are three binders here, including the kind variable k. - See Note [TyVarBndrs, TyVarBinders, TyConBinders, and visibility] in TyCoRep for what the visibility flag means. * Each TyConBinder tyConBinders has a TyVar, and that TyVar may scope over some other part of the TyCon's definition. Eg type T a = a->a we have tyConBinders = [ TvBndr (a:*) AnonTCB ] synTcRhs = a->a So the 'a' scopes over the synTcRhs * From the tyConBinders and tyConResKind we can get the tyConKind E.g for our App example: App :: forall k. (k->*) -> k -> * We get a 'forall' in the kind for each NamedTCB, and an arrow for each AnonTCB tyConKind is the full kind of the TyCon, not just the result kind * tyConArity is the arguments this TyCon must be applied to, to be considered saturated. Here we mean "applied to in the actual Type", not surface syntax; i.e. including implicit kind variables. So it's just (length tyConBinders) -} instance Outputable tv => Outputable (TyVarBndr tv TyConBndrVis) where ppr (TvBndr v AnonTCB) = text "anon" <+> parens (ppr v) ppr (TvBndr v (NamedTCB Required)) = text "req" <+> parens (ppr v) ppr (TvBndr v (NamedTCB Specified)) = text "spec" <+> parens (ppr v) ppr (TvBndr v (NamedTCB Inferred)) = text "inf" <+> parens (ppr v) instance Binary TyConBndrVis where put_ bh AnonTCB = putByte bh 0 put_ bh (NamedTCB vis) = do { putByte bh 1; put_ bh vis } get bh = do { h <- getByte bh ; case h of 0 -> return AnonTCB _ -> do { vis <- get bh; return (NamedTCB vis) } } {- ********************************************************************* * * The TyCon type * * ************************************************************************ -} -- | TyCons represent type constructors. Type constructors are introduced by -- things such as: -- -- 1) Data declarations: @data Foo = ...@ creates the @Foo@ type constructor of -- kind @*@ -- -- 2) Type synonyms: @type Foo = ...@ creates the @Foo@ type constructor -- -- 3) Newtypes: @newtype Foo a = MkFoo ...@ creates the @Foo@ type constructor -- of kind @* -> *@ -- -- 4) Class declarations: @class Foo where@ creates the @Foo@ type constructor -- of kind @*@ -- -- This data type also encodes a number of primitive, built in type constructors -- such as those for function and tuple types. -- If you edit this type, you may need to update the GHC formalism -- See Note [GHC Formalism] in coreSyn/CoreLint.hs data TyCon = -- | The function type constructor, @(->)@ FunTyCon { tyConUnique :: Unique, -- ^ A Unique of this TyCon. Invariant: -- identical to Unique of Name stored in -- tyConName field. tyConName :: Name, -- ^ Name of the constructor -- See Note [The binders/kind/arity fields of a TyCon] tyConBinders :: [TyConBinder], -- ^ Full binders tyConResKind :: Kind, -- ^ Result kind tyConKind :: Kind, -- ^ Kind of this TyCon tyConArity :: Arity, -- ^ Arity tcRepName :: TyConRepName } -- | Algebraic data types, from -- - @data@ declarations -- - @newtype@ declarations -- - data instance declarations -- - type instance declarations -- - the TyCon generated by a class declaration -- - boxed tuples -- - unboxed tuples -- - constraint tuples -- All these constructors are lifted and boxed except unboxed tuples -- which should have an 'UnboxedAlgTyCon' parent. -- Data/newtype/type /families/ are handled by 'FamilyTyCon'. -- See 'AlgTyConRhs' for more information. | AlgTyCon { tyConUnique :: Unique, -- ^ A Unique of this TyCon. Invariant: -- identical to Unique of Name stored in -- tyConName field. tyConName :: Name, -- ^ Name of the constructor -- See Note [The binders/kind/arity fields of a TyCon] tyConBinders :: [TyConBinder], -- ^ Full binders tyConTyVars :: [TyVar], -- ^ TyVar binders tyConResKind :: Kind, -- ^ Result kind tyConKind :: Kind, -- ^ Kind of this TyCon tyConArity :: Arity, -- ^ Arity -- The tyConTyVars scope over: -- -- 1. The 'algTcStupidTheta' -- 2. The cached types in algTyConRhs.NewTyCon -- 3. The family instance types if present -- -- Note that it does /not/ scope over the data -- constructors. tcRoles :: [Role], -- ^ The role for each type variable -- This list has length = tyConArity -- See also Note [TyCon Role signatures] tyConCType :: Maybe CType,-- ^ The C type that should be used -- for this type when using the FFI -- and CAPI algTcGadtSyntax :: Bool, -- ^ Was the data type declared with GADT -- syntax? If so, that doesn't mean it's a -- true GADT; only that the "where" form -- was used. This field is used only to -- guide pretty-printing algTcStupidTheta :: [PredType], -- ^ The \"stupid theta\" for the data -- type (always empty for GADTs). A -- \"stupid theta\" is the context to -- the left of an algebraic type -- declaration, e.g. @Eq a@ in the -- declaration @data Eq a => T a ...@. algTcRhs :: AlgTyConRhs, -- ^ Contains information about the -- data constructors of the algebraic type algTcFields :: FieldLabelEnv, -- ^ Maps a label to information -- about the field algTcParent :: AlgTyConFlav -- ^ Gives the class or family declaration -- 'TyCon' for derived 'TyCon's representing -- class or family instances, respectively. } -- | Represents type synonyms | SynonymTyCon { tyConUnique :: Unique, -- ^ A Unique of this TyCon. Invariant: -- identical to Unique of Name stored in -- tyConName field. tyConName :: Name, -- ^ Name of the constructor -- See Note [The binders/kind/arity fields of a TyCon] tyConBinders :: [TyConBinder], -- ^ Full binders tyConTyVars :: [TyVar], -- ^ TyVar binders tyConResKind :: Kind, -- ^ Result kind tyConKind :: Kind, -- ^ Kind of this TyCon tyConArity :: Arity, -- ^ Arity -- tyConTyVars scope over: synTcRhs tcRoles :: [Role], -- ^ The role for each type variable -- This list has length = tyConArity -- See also Note [TyCon Role signatures] synTcRhs :: Type, -- ^ Contains information about the expansion -- of the synonym synIsTau :: Bool, -- True <=> the RHS of this synonym does not -- have any foralls, after expanding any -- nested synonyms synIsFamFree :: Bool -- True <=> the RHS of this synonym does not mention -- any type synonym families (data families -- are fine), again after expanding any -- nested synonyms } -- | Represents families (both type and data) -- Argument roles are all Nominal | FamilyTyCon { tyConUnique :: Unique, -- ^ A Unique of this TyCon. Invariant: -- identical to Unique of Name stored in -- tyConName field. tyConName :: Name, -- ^ Name of the constructor -- See Note [The binders/kind/arity fields of a TyCon] tyConBinders :: [TyConBinder], -- ^ Full binders tyConTyVars :: [TyVar], -- ^ TyVar binders tyConResKind :: Kind, -- ^ Result kind tyConKind :: Kind, -- ^ Kind of this TyCon tyConArity :: Arity, -- ^ Arity -- tyConTyVars connect an associated family TyCon -- with its parent class; see TcValidity.checkConsistentFamInst famTcResVar :: Maybe Name, -- ^ Name of result type variable, used -- for pretty-printing with --show-iface -- and for reifying TyCon in Template -- Haskell famTcFlav :: FamTyConFlav, -- ^ Type family flavour: open, closed, -- abstract, built-in. See comments for -- FamTyConFlav famTcParent :: Maybe Class, -- ^ For *associated* type/data families -- The class in whose declaration the family is declared -- See Note [Associated families and their parent class] famTcInj :: Injectivity -- ^ is this a type family injective in -- its type variables? Nothing if no -- injectivity annotation was given } -- | Primitive types; cannot be defined in Haskell. This includes -- the usual suspects (such as @Int#@) as well as foreign-imported -- types and kinds (@*@, @#@, and @?@) | PrimTyCon { tyConUnique :: Unique, -- ^ A Unique of this TyCon. Invariant: -- identical to Unique of Name stored in -- tyConName field. tyConName :: Name, -- ^ Name of the constructor -- See Note [The binders/kind/arity fields of a TyCon] tyConBinders :: [TyConBinder], -- ^ Full binders tyConResKind :: Kind, -- ^ Result kind tyConKind :: Kind, -- ^ Kind of this TyCon tyConArity :: Arity, -- ^ Arity tcRoles :: [Role], -- ^ The role for each type variable -- This list has length = tyConArity -- See also Note [TyCon Role signatures] isUnlifted :: Bool, -- ^ Most primitive tycons are unlifted (may -- not contain bottom) but other are lifted, -- e.g. @RealWorld@ -- Only relevant if tyConKind = * primRepName :: Maybe TyConRepName -- Only relevant for kind TyCons -- i.e, *, #, ? } -- | Represents promoted data constructor. | PromotedDataCon { -- See Note [Promoted data constructors] tyConUnique :: Unique, -- ^ Same Unique as the data constructor tyConName :: Name, -- ^ Same Name as the data constructor -- See Note [The binders/kind/arity fields of a TyCon] tyConBinders :: [TyConBinder], -- ^ Full binders tyConResKind :: Kind, -- ^ Result kind tyConKind :: Kind, -- ^ Kind of this TyCon tyConArity :: Arity, -- ^ Arity tcRoles :: [Role], -- ^ Roles: N for kind vars, R for type vars dataCon :: DataCon, -- ^ Corresponding data constructor tcRepName :: TyConRepName, promDcRepInfo :: RuntimeRepInfo -- ^ See comments with 'RuntimeRepInfo' } -- | These exist only during type-checking. See Note [How TcTyCons work] -- in TcTyClsDecls | TcTyCon { tyConUnique :: Unique, tyConName :: Name, -- See Note [The binders/kind/arity fields of a TyCon] tyConBinders :: [TyConBinder], -- ^ Full binders tyConTyVars :: [TyVar], -- ^ TyVar binders tyConResKind :: Kind, -- ^ Result kind tyConKind :: Kind, -- ^ Kind of this TyCon tyConArity :: Arity, -- ^ Arity tcTyConScopedTyVars :: [(Name,TyVar)], -- ^ Scoped tyvars over the tycon's body -- See Note [How TcTyCons work] in TcTyClsDecls -- Order does *not* matter. tcTyConUserTyVars :: SDoc, -- ^ Original, user-written tycon tyvars tcTyConFlavour :: TyConFlavour -- ^ What sort of 'TyCon' this represents. } -- | Represents right-hand-sides of 'TyCon's for algebraic types data AlgTyConRhs -- | Says that we know nothing about this data type, except that -- it's represented by a pointer. Used when we export a data type -- abstractly into an .hi file. = AbstractTyCon -- | Information about those 'TyCon's derived from a @data@ -- declaration. This includes data types with no constructors at -- all. | DataTyCon { data_cons :: [DataCon], -- ^ The data type constructors; can be empty if the -- user declares the type to have no constructors -- -- INVARIANT: Kept in order of increasing 'DataCon' -- tag (see the tag assignment in mkTyConTagMap) data_cons_size :: Int, -- ^ Cached value: length data_cons is_enum :: Bool -- ^ Cached value: is this an enumeration type? -- See Note [Enumeration types] } | TupleTyCon { -- A boxed, unboxed, or constraint tuple data_con :: DataCon, -- NB: it can be an *unboxed* tuple tup_sort :: TupleSort -- ^ Is this a boxed, unboxed or constraint -- tuple? } -- | An unboxed sum type. | SumTyCon { data_cons :: [DataCon], data_cons_size :: Int -- ^ Cached value: length data_cons } -- | Information about those 'TyCon's derived from a @newtype@ declaration | NewTyCon { data_con :: DataCon, -- ^ The unique constructor for the @newtype@. -- It has no existentials nt_rhs :: Type, -- ^ Cached value: the argument type of the -- constructor, which is just the representation -- type of the 'TyCon' (remember that @newtype@s -- do not exist at runtime so need a different -- representation type). -- -- The free 'TyVar's of this type are the -- 'tyConTyVars' from the corresponding 'TyCon' nt_etad_rhs :: ([TyVar], Type), -- ^ Same as the 'nt_rhs', but this time eta-reduced. -- Hence the list of 'TyVar's in this field may be -- shorter than the declared arity of the 'TyCon'. -- See Note [Newtype eta] nt_co :: CoAxiom Unbranched -- The axiom coercion that creates the @newtype@ -- from the representation 'Type'. -- See Note [Newtype coercions] -- Invariant: arity = #tvs in nt_etad_rhs; -- See Note [Newtype eta] -- Watch out! If any newtypes become transparent -- again check Trac #1072. } mkSumTyConRhs :: [DataCon] -> AlgTyConRhs mkSumTyConRhs data_cons = SumTyCon data_cons (length data_cons) mkDataTyConRhs :: [DataCon] -> AlgTyConRhs mkDataTyConRhs cons = DataTyCon { data_cons = cons, data_cons_size = length cons, is_enum = not (null cons) && all is_enum_con cons -- See Note [Enumeration types] in TyCon } where is_enum_con con | (_univ_tvs, ex_tvs, eq_spec, theta, arg_tys, _res) <- dataConFullSig con = null ex_tvs && null eq_spec && null theta && null arg_tys -- | Some promoted datacons signify extra info relevant to GHC. For example, -- the @IntRep@ constructor of @RuntimeRep@ corresponds to the 'IntRep' -- constructor of 'PrimRep'. This data structure allows us to store this -- information right in the 'TyCon'. The other approach would be to look -- up things like @RuntimeRep@'s @PrimRep@ by known-key every time. data RuntimeRepInfo = NoRRI -- ^ an ordinary promoted data con | RuntimeRep ([Type] -> [PrimRep]) -- ^ A constructor of @RuntimeRep@. The argument to the function should -- be the list of arguments to the promoted datacon. | VecCount Int -- ^ A constructor of @VecCount@ | VecElem PrimElemRep -- ^ A constructor of @VecElem@ -- | Extract those 'DataCon's that we are able to learn about. Note -- that visibility in this sense does not correspond to visibility in -- the context of any particular user program! visibleDataCons :: AlgTyConRhs -> [DataCon] visibleDataCons (AbstractTyCon {}) = [] visibleDataCons (DataTyCon{ data_cons = cs }) = cs visibleDataCons (NewTyCon{ data_con = c }) = [c] visibleDataCons (TupleTyCon{ data_con = c }) = [c] visibleDataCons (SumTyCon{ data_cons = cs }) = cs -- ^ Both type classes as well as family instances imply implicit -- type constructors. These implicit type constructors refer to their parent -- structure (ie, the class or family from which they derive) using a type of -- the following form. data AlgTyConFlav = -- | An ordinary type constructor has no parent. VanillaAlgTyCon TyConRepName -- | An unboxed type constructor. The TyConRepName is a Maybe since we -- currently don't allow unboxed sums to be Typeable since there are too -- many of them. See #13276. | UnboxedAlgTyCon (Maybe TyConRepName) -- | Type constructors representing a class dictionary. -- See Note [ATyCon for classes] in TyCoRep | ClassTyCon Class -- INVARIANT: the classTyCon of this Class is the -- current tycon TyConRepName -- | Type constructors representing an *instance* of a *data* family. -- Parameters: -- -- 1) The type family in question -- -- 2) Instance types; free variables are the 'tyConTyVars' -- of the current 'TyCon' (not the family one). INVARIANT: -- the number of types matches the arity of the family 'TyCon' -- -- 3) A 'CoTyCon' identifying the representation -- type with the type instance family | DataFamInstTyCon -- See Note [Data type families] (CoAxiom Unbranched) -- The coercion axiom. -- A *Representational* coercion, -- of kind T ty1 ty2 ~R R:T a b c -- where T is the family TyCon, -- and R:T is the representation TyCon (ie this one) -- and a,b,c are the tyConTyVars of this TyCon -- -- BUT may be eta-reduced; see TcInstDcls -- Note [Eta reduction for data family axioms] -- Cached fields of the CoAxiom, but adjusted to -- use the tyConTyVars of this TyCon TyCon -- The family TyCon [Type] -- Argument types (mentions the tyConTyVars of this TyCon) -- No shorter in length than the tyConTyVars of the family TyCon -- How could it be longer? See [Arity of data families] in FamInstEnv -- E.g. data instance T [a] = ... -- gives a representation tycon: -- data R:TList a = ... -- axiom co a :: T [a] ~ R:TList a -- with R:TList's algTcParent = DataFamInstTyCon T [a] co instance Outputable AlgTyConFlav where ppr (VanillaAlgTyCon {}) = text "Vanilla ADT" ppr (UnboxedAlgTyCon {}) = text "Unboxed ADT" ppr (ClassTyCon cls _) = text "Class parent" <+> ppr cls ppr (DataFamInstTyCon _ tc tys) = text "Family parent (family instance)" <+> ppr tc <+> sep (map pprType tys) -- | Checks the invariants of a 'AlgTyConFlav' given the appropriate type class -- name, if any okParent :: Name -> AlgTyConFlav -> Bool okParent _ (VanillaAlgTyCon {}) = True okParent _ (UnboxedAlgTyCon {}) = True okParent tc_name (ClassTyCon cls _) = tc_name == tyConName (classTyCon cls) okParent _ (DataFamInstTyCon _ fam_tc tys) = tys `lengthAtLeast` tyConArity fam_tc isNoParent :: AlgTyConFlav -> Bool isNoParent (VanillaAlgTyCon {}) = True isNoParent _ = False -------------------- data Injectivity = NotInjective | Injective [Bool] -- 1-1 with tyConTyVars (incl kind vars) deriving( Eq ) -- | Information pertaining to the expansion of a type synonym (@type@) data FamTyConFlav = -- | Represents an open type family without a fixed right hand -- side. Additional instances can appear at any time. -- -- These are introduced by either a top level declaration: -- -- > data family T a :: * -- -- Or an associated data type declaration, within a class declaration: -- -- > class C a b where -- > data T b :: * DataFamilyTyCon TyConRepName -- | An open type synonym family e.g. @type family F x y :: * -> *@ | OpenSynFamilyTyCon -- | A closed type synonym family e.g. -- @type family F x where { F Int = Bool }@ | ClosedSynFamilyTyCon (Maybe (CoAxiom Branched)) -- See Note [Closed type families] -- | A closed type synonym family declared in an hs-boot file with -- type family F a where .. | AbstractClosedSynFamilyTyCon -- | Built-in type family used by the TypeNats solver | BuiltInSynFamTyCon BuiltInSynFamily instance Outputable FamTyConFlav where ppr (DataFamilyTyCon n) = text "data family" <+> ppr n ppr OpenSynFamilyTyCon = text "open type family" ppr (ClosedSynFamilyTyCon Nothing) = text "closed type family" ppr (ClosedSynFamilyTyCon (Just coax)) = text "closed type family" <+> ppr coax ppr AbstractClosedSynFamilyTyCon = text "abstract closed type family" ppr (BuiltInSynFamTyCon _) = text "built-in type family" {- Note [Closed type families] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ * In an open type family you can add new instances later. This is the usual case. * In a closed type family you can only put equations where the family is defined. A non-empty closed type family has a single axiom with multiple branches, stored in the 'ClosedSynFamilyTyCon' constructor. A closed type family with no equations does not have an axiom, because there is nothing for the axiom to prove! Note [Promoted data constructors] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ All data constructors can be promoted to become a type constructor, via the PromotedDataCon alternative in TyCon. * The TyCon promoted from a DataCon has the *same* Name and Unique as the DataCon. Eg. If the data constructor Data.Maybe.Just(unique 78, say) is promoted to a TyCon whose name is Data.Maybe.Just(unique 78) * Small note: We promote the *user* type of the DataCon. Eg data T = MkT {-# UNPACK #-} !(Bool, Bool) The promoted kind is MkT :: (Bool,Bool) -> T *not* MkT :: Bool -> Bool -> T Note [Enumeration types] ~~~~~~~~~~~~~~~~~~~~~~~~ We define datatypes with no constructors to *not* be enumerations; this fixes trac #2578, Otherwise we end up generating an empty table for <mod>_<type>_closure_tbl which is used by tagToEnum# to map Int# to constructors in an enumeration. The empty table apparently upset the linker. Moreover, all the data constructor must be enumerations, meaning they have type (forall abc. T a b c). GADTs are not enumerations. For example consider data T a where T1 :: T Int T2 :: T Bool T3 :: T a What would [T1 ..] be? [T1,T3] :: T Int? Easiest thing is to exclude them. See Trac #4528. Note [Newtype coercions] ~~~~~~~~~~~~~~~~~~~~~~~~ The NewTyCon field nt_co is a CoAxiom which is used for coercing from the representation type of the newtype, to the newtype itself. For example, newtype T a = MkT (a -> a) the NewTyCon for T will contain nt_co = CoT where CoT t : T t ~ t -> t. In the case that the right hand side is a type application ending with the same type variables as the left hand side, we "eta-contract" the coercion. So if we had newtype S a = MkT [a] then we would generate the arity 0 axiom CoS : S ~ []. The primary reason we do this is to make newtype deriving cleaner. In the paper we'd write axiom CoT : (forall t. T t) ~ (forall t. [t]) and then when we used CoT at a particular type, s, we'd say CoT @ s which encodes as (TyConApp instCoercionTyCon [TyConApp CoT [], s]) Note [Newtype eta] ~~~~~~~~~~~~~~~~~~ Consider newtype Parser a = MkParser (IO a) deriving Monad Are these two types equal (to Core)? Monad Parser Monad IO which we need to make the derived instance for Monad Parser. Well, yes. But to see that easily we eta-reduce the RHS type of Parser, in this case to ([], Froogle), so that even unsaturated applications of Parser will work right. This eta reduction is done when the type constructor is built, and cached in NewTyCon. Here's an example that I think showed up in practice Source code: newtype T a = MkT [a] newtype Foo m = MkFoo (forall a. m a -> Int) w1 :: Foo [] w1 = ... w2 :: Foo T w2 = MkFoo (\(MkT x) -> case w1 of MkFoo f -> f x) After desugaring, and discarding the data constructors for the newtypes, we get: w2 = w1 `cast` Foo CoT so the coercion tycon CoT must have kind: T ~ [] and arity: 0 ************************************************************************ * * TyConRepName * * ********************************************************************* -} type TyConRepName = Name -- The Name of the top-level declaration -- $tcMaybe :: Data.Typeable.Internal.TyCon -- $tcMaybe = TyCon { tyConName = "Maybe", ... } tyConRepName_maybe :: TyCon -> Maybe TyConRepName tyConRepName_maybe (FunTyCon { tcRepName = rep_nm }) = Just rep_nm tyConRepName_maybe (PrimTyCon { primRepName = mb_rep_nm }) = mb_rep_nm tyConRepName_maybe (AlgTyCon { algTcParent = parent }) | VanillaAlgTyCon rep_nm <- parent = Just rep_nm | ClassTyCon _ rep_nm <- parent = Just rep_nm | UnboxedAlgTyCon rep_nm <- parent = rep_nm tyConRepName_maybe (FamilyTyCon { famTcFlav = DataFamilyTyCon rep_nm }) = Just rep_nm tyConRepName_maybe (PromotedDataCon { dataCon = dc, tcRepName = rep_nm }) | isUnboxedSumCon dc -- see #13276 = Nothing | otherwise = Just rep_nm tyConRepName_maybe _ = Nothing -- | Make a 'Name' for the 'Typeable' representation of the given wired-in type mkPrelTyConRepName :: Name -> TyConRepName -- See Note [Grand plan for Typeable] in 'TcTypeable' in TcTypeable. mkPrelTyConRepName tc_name -- Prelude tc_name is always External, -- so nameModule will work = mkExternalName rep_uniq rep_mod rep_occ (nameSrcSpan tc_name) where name_occ = nameOccName tc_name name_mod = nameModule tc_name name_uniq = nameUnique tc_name rep_uniq | isTcOcc name_occ = tyConRepNameUnique name_uniq | otherwise = dataConTyRepNameUnique name_uniq (rep_mod, rep_occ) = tyConRepModOcc name_mod name_occ -- | The name (and defining module) for the Typeable representation (TyCon) of a -- type constructor. -- -- See Note [Grand plan for Typeable] in 'TcTypeable' in TcTypeable. tyConRepModOcc :: Module -> OccName -> (Module, OccName) tyConRepModOcc tc_module tc_occ = (rep_module, mkTyConRepOcc tc_occ) where rep_module | tc_module == gHC_PRIM = gHC_TYPES | otherwise = tc_module {- ********************************************************************* * * PrimRep * * ************************************************************************ Note [rep swamp] GHC has a rich selection of types that represent "primitive types" of one kind or another. Each of them makes a different set of distinctions, and mostly the differences are for good reasons, although it's probably true that we could merge some of these. Roughly in order of "includes more information": - A Width (cmm/CmmType) is simply a binary value with the specified number of bits. It may represent a signed or unsigned integer, a floating-point value, or an address. data Width = W8 | W16 | W32 | W64 | W80 | W128 - Size, which is used in the native code generator, is Width + floating point information. data Size = II8 | II16 | II32 | II64 | FF32 | FF64 | FF80 it is necessary because e.g. the instruction to move a 64-bit float on x86 (movsd) is different from the instruction to move a 64-bit integer (movq), so the mov instruction is parameterised by Size. - CmmType wraps Width with more information: GC ptr, float, or other value. data CmmType = CmmType CmmCat Width data CmmCat -- "Category" (not exported) = GcPtrCat -- GC pointer | BitsCat -- Non-pointer | FloatCat -- Float It is important to have GcPtr information in Cmm, since we generate info tables containing pointerhood for the GC from this. As for why we have float (and not signed/unsigned) here, see Note [Signed vs unsigned]. - ArgRep makes only the distinctions necessary for the call and return conventions of the STG machine. It is essentially CmmType + void. - PrimRep makes a few more distinctions than ArgRep: it divides non-GC-pointers into signed/unsigned and addresses, information that is necessary for passing these values to foreign functions. There's another tension here: whether the type encodes its size in bytes, or whether its size depends on the machine word size. Width and CmmType have the size built-in, whereas ArgRep and PrimRep do not. This means to turn an ArgRep/PrimRep into a CmmType requires DynFlags. On the other hand, CmmType includes some "nonsense" values, such as CmmType GcPtrCat W32 on a 64-bit machine. -} -- | A 'PrimRep' is an abstraction of a type. It contains information that -- the code generator needs in order to pass arguments, return results, -- and store values of this type. data PrimRep = VoidRep | LiftedRep | UnliftedRep -- ^ Unlifted pointer | IntRep -- ^ Signed, word-sized value | WordRep -- ^ Unsigned, word-sized value | Int64Rep -- ^ Signed, 64 bit value (with 32-bit words only) | Word64Rep -- ^ Unsigned, 64 bit value (with 32-bit words only) | AddrRep -- ^ A pointer, but /not/ to a Haskell value (use '(Un)liftedRep') | FloatRep | DoubleRep | VecRep Int PrimElemRep -- ^ A vector deriving( Eq, Show ) data PrimElemRep = Int8ElemRep | Int16ElemRep | Int32ElemRep | Int64ElemRep | Word8ElemRep | Word16ElemRep | Word32ElemRep | Word64ElemRep | FloatElemRep | DoubleElemRep deriving( Eq, Show ) instance Outputable PrimRep where ppr r = text (show r) instance Outputable PrimElemRep where ppr r = text (show r) isVoidRep :: PrimRep -> Bool isVoidRep VoidRep = True isVoidRep _other = False isGcPtrRep :: PrimRep -> Bool isGcPtrRep LiftedRep = True isGcPtrRep UnliftedRep = True isGcPtrRep _ = False -- | The size of a 'PrimRep' in bytes. -- -- This applies also when used in a constructor, where we allow packing the -- fields. For instance, in @data Foo = Foo Float# Float#@ the two fields will -- take only 8 bytes, which for 64-bit arch will be equal to 1 word. -- See also mkVirtHeapOffsetsWithPadding for details of how data fields are -- layed out. primRepSizeB :: DynFlags -> PrimRep -> Int primRepSizeB dflags IntRep = wORD_SIZE dflags primRepSizeB dflags WordRep = wORD_SIZE dflags primRepSizeB _ Int64Rep = wORD64_SIZE primRepSizeB _ Word64Rep = wORD64_SIZE primRepSizeB _ FloatRep = fLOAT_SIZE primRepSizeB dflags DoubleRep = dOUBLE_SIZE dflags primRepSizeB dflags AddrRep = wORD_SIZE dflags primRepSizeB dflags LiftedRep = wORD_SIZE dflags primRepSizeB dflags UnliftedRep = wORD_SIZE dflags primRepSizeB _ VoidRep = 0 primRepSizeB _ (VecRep len rep) = len * primElemRepSizeB rep primElemRepSizeB :: PrimElemRep -> Int primElemRepSizeB Int8ElemRep = 1 primElemRepSizeB Int16ElemRep = 2 primElemRepSizeB Int32ElemRep = 4 primElemRepSizeB Int64ElemRep = 8 primElemRepSizeB Word8ElemRep = 1 primElemRepSizeB Word16ElemRep = 2 primElemRepSizeB Word32ElemRep = 4 primElemRepSizeB Word64ElemRep = 8 primElemRepSizeB FloatElemRep = 4 primElemRepSizeB DoubleElemRep = 8 -- | Return if Rep stands for floating type, -- returns Nothing for vector types. primRepIsFloat :: PrimRep -> Maybe Bool primRepIsFloat FloatRep = Just True primRepIsFloat DoubleRep = Just True primRepIsFloat (VecRep _ _) = Nothing primRepIsFloat _ = Just False {- ************************************************************************ * * Field labels * * ************************************************************************ -} -- | The labels for the fields of this particular 'TyCon' tyConFieldLabels :: TyCon -> [FieldLabel] tyConFieldLabels tc = dFsEnvElts $ tyConFieldLabelEnv tc -- | The labels for the fields of this particular 'TyCon' tyConFieldLabelEnv :: TyCon -> FieldLabelEnv tyConFieldLabelEnv tc | isAlgTyCon tc = algTcFields tc | otherwise = emptyDFsEnv -- | Look up a field label belonging to this 'TyCon' lookupTyConFieldLabel :: FieldLabelString -> TyCon -> Maybe FieldLabel lookupTyConFieldLabel lbl tc = lookupDFsEnv (tyConFieldLabelEnv tc) lbl -- | Make a map from strings to FieldLabels from all the data -- constructors of this algebraic tycon fieldsOfAlgTcRhs :: AlgTyConRhs -> FieldLabelEnv fieldsOfAlgTcRhs rhs = mkDFsEnv [ (flLabel fl, fl) | fl <- dataConsFields (visibleDataCons rhs) ] where -- Duplicates in this list will be removed by 'mkFsEnv' dataConsFields dcs = concatMap dataConFieldLabels dcs {- ************************************************************************ * * \subsection{TyCon Construction} * * ************************************************************************ Note: the TyCon constructors all take a Kind as one argument, even though they could, in principle, work out their Kind from their other arguments. But to do so they need functions from Types, and that makes a nasty module mutual-recursion. And they aren't called from many places. So we compromise, and move their Kind calculation to the call site. -} -- | Given the name of the function type constructor and it's kind, create the -- corresponding 'TyCon'. It is recomended to use 'TyCoRep.funTyCon' if you want -- this functionality mkFunTyCon :: Name -> [TyConBinder] -> Name -> TyCon mkFunTyCon name binders rep_nm = FunTyCon { tyConUnique = nameUnique name, tyConName = name, tyConBinders = binders, tyConResKind = liftedTypeKind, tyConKind = mkTyConKind binders liftedTypeKind, tyConArity = length binders, tcRepName = rep_nm } -- | This is the making of an algebraic 'TyCon'. Notably, you have to -- pass in the generic (in the -XGenerics sense) information about the -- type constructor - you can get hold of it easily (see Generics -- module) mkAlgTyCon :: Name -> [TyConBinder] -- ^ Binders of the 'TyCon' -> Kind -- ^ Result kind -> [Role] -- ^ The roles for each TyVar -> Maybe CType -- ^ The C type this type corresponds to -- when using the CAPI FFI -> [PredType] -- ^ Stupid theta: see 'algTcStupidTheta' -> AlgTyConRhs -- ^ Information about data constructors -> AlgTyConFlav -- ^ What flavour is it? -- (e.g. vanilla, type family) -> Bool -- ^ Was the 'TyCon' declared with GADT syntax? -> TyCon mkAlgTyCon name binders res_kind roles cType stupid rhs parent gadt_syn = AlgTyCon { tyConName = name, tyConUnique = nameUnique name, tyConBinders = binders, tyConResKind = res_kind, tyConKind = mkTyConKind binders res_kind, tyConArity = length binders, tyConTyVars = binderVars binders, tcRoles = roles, tyConCType = cType, algTcStupidTheta = stupid, algTcRhs = rhs, algTcFields = fieldsOfAlgTcRhs rhs, algTcParent = ASSERT2( okParent name parent, ppr name $$ ppr parent ) parent, algTcGadtSyntax = gadt_syn } -- | Simpler specialization of 'mkAlgTyCon' for classes mkClassTyCon :: Name -> [TyConBinder] -> [Role] -> AlgTyConRhs -> Class -> Name -> TyCon mkClassTyCon name binders roles rhs clas tc_rep_name = mkAlgTyCon name binders constraintKind roles Nothing [] rhs (ClassTyCon clas tc_rep_name) False mkTupleTyCon :: Name -> [TyConBinder] -> Kind -- ^ Result kind of the 'TyCon' -> Arity -- ^ Arity of the tuple 'TyCon' -> DataCon -> TupleSort -- ^ Whether the tuple is boxed or unboxed -> AlgTyConFlav -> TyCon mkTupleTyCon name binders res_kind arity con sort parent = AlgTyCon { tyConUnique = nameUnique name, tyConName = name, tyConBinders = binders, tyConTyVars = binderVars binders, tyConResKind = res_kind, tyConKind = mkTyConKind binders res_kind, tyConArity = arity, tcRoles = replicate arity Representational, tyConCType = Nothing, algTcGadtSyntax = False, algTcStupidTheta = [], algTcRhs = TupleTyCon { data_con = con, tup_sort = sort }, algTcFields = emptyDFsEnv, algTcParent = parent } mkSumTyCon :: Name -> [TyConBinder] -> Kind -- ^ Kind of the resulting 'TyCon' -> Arity -- ^ Arity of the sum -> [TyVar] -- ^ 'TyVar's scoped over: see 'tyConTyVars' -> [DataCon] -> AlgTyConFlav -> TyCon mkSumTyCon name binders res_kind arity tyvars cons parent = AlgTyCon { tyConUnique = nameUnique name, tyConName = name, tyConBinders = binders, tyConTyVars = tyvars, tyConResKind = res_kind, tyConKind = mkTyConKind binders res_kind, tyConArity = arity, tcRoles = replicate arity Representational, tyConCType = Nothing, algTcGadtSyntax = False, algTcStupidTheta = [], algTcRhs = mkSumTyConRhs cons, algTcFields = emptyDFsEnv, algTcParent = parent } -- | Makes a tycon suitable for use during type-checking. It stores -- a variety of details about the definition of the TyCon, but no -- right-hand side. It lives only during the type-checking of a -- mutually-recursive group of tycons; it is then zonked to a proper -- TyCon in zonkTcTyCon. -- See also Note [Kind checking recursive type and class declarations] -- in TcTyClsDecls. mkTcTyCon :: Name -> SDoc -- ^ user-written tycon tyvars -> [TyConBinder] -> Kind -- ^ /result/ kind only -> [(Name,TcTyVar)] -- ^ Scoped type variables; -- see Note [How TcTyCons work] in TcTyClsDecls -> TyConFlavour -- ^ What sort of 'TyCon' this represents -> TyCon mkTcTyCon name tyvars binders res_kind scoped_tvs flav = TcTyCon { tyConUnique = getUnique name , tyConName = name , tyConTyVars = binderVars binders , tyConBinders = binders , tyConResKind = res_kind , tyConKind = mkTyConKind binders res_kind , tyConArity = length binders , tcTyConScopedTyVars = scoped_tvs , tcTyConFlavour = flav , tcTyConUserTyVars = tyvars } -- | Create an unlifted primitive 'TyCon', such as @Int#@. mkPrimTyCon :: Name -> [TyConBinder] -> Kind -- ^ /result/ kind, never levity-polymorphic -> [Role] -> TyCon mkPrimTyCon name binders res_kind roles = mkPrimTyCon' name binders res_kind roles True (Just $ mkPrelTyConRepName name) -- | Kind constructors mkKindTyCon :: Name -> [TyConBinder] -> Kind -- ^ /result/ kind -> [Role] -> Name -> TyCon mkKindTyCon name binders res_kind roles rep_nm = tc where tc = mkPrimTyCon' name binders res_kind roles False (Just rep_nm) -- | Create a lifted primitive 'TyCon' such as @RealWorld@ mkLiftedPrimTyCon :: Name -> [TyConBinder] -> Kind -- ^ /result/ kind -> [Role] -> TyCon mkLiftedPrimTyCon name binders res_kind roles = mkPrimTyCon' name binders res_kind roles False (Just rep_nm) where rep_nm = mkPrelTyConRepName name mkPrimTyCon' :: Name -> [TyConBinder] -> Kind -- ^ /result/ kind, never levity-polymorphic -- (If you need a levity-polymorphic PrimTyCon, change -- isTcLevPoly.) -> [Role] -> Bool -> Maybe TyConRepName -> TyCon mkPrimTyCon' name binders res_kind roles is_unlifted rep_nm = PrimTyCon { tyConName = name, tyConUnique = nameUnique name, tyConBinders = binders, tyConResKind = res_kind, tyConKind = mkTyConKind binders res_kind, tyConArity = length roles, tcRoles = roles, isUnlifted = is_unlifted, primRepName = rep_nm } -- | Create a type synonym 'TyCon' mkSynonymTyCon :: Name -> [TyConBinder] -> Kind -- ^ /result/ kind -> [Role] -> Type -> Bool -> Bool -> TyCon mkSynonymTyCon name binders res_kind roles rhs is_tau is_fam_free = SynonymTyCon { tyConName = name, tyConUnique = nameUnique name, tyConBinders = binders, tyConResKind = res_kind, tyConKind = mkTyConKind binders res_kind, tyConArity = length binders, tyConTyVars = binderVars binders, tcRoles = roles, synTcRhs = rhs, synIsTau = is_tau, synIsFamFree = is_fam_free } -- | Create a type family 'TyCon' mkFamilyTyCon :: Name -> [TyConBinder] -> Kind -- ^ /result/ kind -> Maybe Name -> FamTyConFlav -> Maybe Class -> Injectivity -> TyCon mkFamilyTyCon name binders res_kind resVar flav parent inj = FamilyTyCon { tyConUnique = nameUnique name , tyConName = name , tyConBinders = binders , tyConResKind = res_kind , tyConKind = mkTyConKind binders res_kind , tyConArity = length binders , tyConTyVars = binderVars binders , famTcResVar = resVar , famTcFlav = flav , famTcParent = parent , famTcInj = inj } -- | Create a promoted data constructor 'TyCon' -- Somewhat dodgily, we give it the same Name -- as the data constructor itself; when we pretty-print -- the TyCon we add a quote; see the Outputable TyCon instance mkPromotedDataCon :: DataCon -> Name -> TyConRepName -> [TyConBinder] -> Kind -> [Role] -> RuntimeRepInfo -> TyCon mkPromotedDataCon con name rep_name binders res_kind roles rep_info = PromotedDataCon { tyConUnique = nameUnique name, tyConName = name, tyConArity = length roles, tcRoles = roles, tyConBinders = binders, tyConResKind = res_kind, tyConKind = mkTyConKind binders res_kind, dataCon = con, tcRepName = rep_name, promDcRepInfo = rep_info } isFunTyCon :: TyCon -> Bool isFunTyCon (FunTyCon {}) = True isFunTyCon _ = False -- | Test if the 'TyCon' is algebraic but abstract (invisible data constructors) isAbstractTyCon :: TyCon -> Bool isAbstractTyCon (AlgTyCon { algTcRhs = AbstractTyCon }) = True isAbstractTyCon _ = False -- | Make a fake, recovery 'TyCon' from an existing one. -- Used when recovering from errors makeRecoveryTyCon :: TyCon -> TyCon makeRecoveryTyCon tc = mkTcTyCon (tyConName tc) empty (tyConBinders tc) (tyConResKind tc) [{- no scoped vars -}] (tyConFlavour tc) -- | Does this 'TyCon' represent something that cannot be defined in Haskell? isPrimTyCon :: TyCon -> Bool isPrimTyCon (PrimTyCon {}) = True isPrimTyCon _ = False -- | Is this 'TyCon' unlifted (i.e. cannot contain bottom)? Note that this can -- only be true for primitive and unboxed-tuple 'TyCon's isUnliftedTyCon :: TyCon -> Bool isUnliftedTyCon (PrimTyCon {isUnlifted = is_unlifted}) = is_unlifted isUnliftedTyCon (AlgTyCon { algTcRhs = rhs } ) | TupleTyCon { tup_sort = sort } <- rhs = not (isBoxed (tupleSortBoxity sort)) isUnliftedTyCon (AlgTyCon { algTcRhs = rhs } ) | SumTyCon {} <- rhs = True isUnliftedTyCon _ = False -- | Returns @True@ if the supplied 'TyCon' resulted from either a -- @data@ or @newtype@ declaration isAlgTyCon :: TyCon -> Bool isAlgTyCon (AlgTyCon {}) = True isAlgTyCon _ = False -- | Returns @True@ for vanilla AlgTyCons -- that is, those created -- with a @data@ or @newtype@ declaration. isVanillaAlgTyCon :: TyCon -> Bool isVanillaAlgTyCon (AlgTyCon { algTcParent = VanillaAlgTyCon _ }) = True isVanillaAlgTyCon _ = False isDataTyCon :: TyCon -> Bool -- ^ Returns @True@ for data types that are /definitely/ represented by -- heap-allocated constructors. These are scrutinised by Core-level -- @case@ expressions, and they get info tables allocated for them. -- -- Generally, the function will be true for all @data@ types and false -- for @newtype@s, unboxed tuples, unboxed sums and type family -- 'TyCon's. But it is not guaranteed to return @True@ in all cases -- that it could. -- -- NB: for a data type family, only the /instance/ 'TyCon's -- get an info table. The family declaration 'TyCon' does not isDataTyCon (AlgTyCon {algTcRhs = rhs}) = case rhs of TupleTyCon { tup_sort = sort } -> isBoxed (tupleSortBoxity sort) SumTyCon {} -> False DataTyCon {} -> True NewTyCon {} -> False AbstractTyCon {} -> False -- We don't know, so return False isDataTyCon _ = False -- | 'isInjectiveTyCon' is true of 'TyCon's for which this property holds -- (where X is the role passed in): -- If (T a1 b1 c1) ~X (T a2 b2 c2), then (a1 ~X1 a2), (b1 ~X2 b2), and (c1 ~X3 c2) -- (where X1, X2, and X3, are the roles given by tyConRolesX tc X) -- See also Note [Decomposing equality] in TcCanonical isInjectiveTyCon :: TyCon -> Role -> Bool isInjectiveTyCon _ Phantom = False isInjectiveTyCon (FunTyCon {}) _ = True isInjectiveTyCon (AlgTyCon {}) Nominal = True isInjectiveTyCon (AlgTyCon {algTcRhs = rhs}) Representational = isGenInjAlgRhs rhs isInjectiveTyCon (SynonymTyCon {}) _ = False isInjectiveTyCon (FamilyTyCon { famTcFlav = DataFamilyTyCon _ }) Nominal = True isInjectiveTyCon (FamilyTyCon { famTcInj = Injective inj }) Nominal = and inj isInjectiveTyCon (FamilyTyCon {}) _ = False isInjectiveTyCon (PrimTyCon {}) _ = True isInjectiveTyCon (PromotedDataCon {}) _ = True isInjectiveTyCon (TcTyCon {}) _ = True -- Reply True for TcTyCon to minimise knock on type errors -- See Note [How TcTyCons work] item (1) in TcTyClsDecls -- | 'isGenerativeTyCon' is true of 'TyCon's for which this property holds -- (where X is the role passed in): -- If (T tys ~X t), then (t's head ~X T). -- See also Note [Decomposing equality] in TcCanonical isGenerativeTyCon :: TyCon -> Role -> Bool isGenerativeTyCon (FamilyTyCon { famTcFlav = DataFamilyTyCon _ }) Nominal = True isGenerativeTyCon (FamilyTyCon {}) _ = False -- in all other cases, injectivity implies generativity isGenerativeTyCon tc r = isInjectiveTyCon tc r -- | Is this an 'AlgTyConRhs' of a 'TyCon' that is generative and injective -- with respect to representational equality? isGenInjAlgRhs :: AlgTyConRhs -> Bool isGenInjAlgRhs (TupleTyCon {}) = True isGenInjAlgRhs (SumTyCon {}) = True isGenInjAlgRhs (DataTyCon {}) = True isGenInjAlgRhs (AbstractTyCon {}) = False isGenInjAlgRhs (NewTyCon {}) = False -- | Is this 'TyCon' that for a @newtype@ isNewTyCon :: TyCon -> Bool isNewTyCon (AlgTyCon {algTcRhs = NewTyCon {}}) = True isNewTyCon _ = False -- | Take a 'TyCon' apart into the 'TyVar's it scopes over, the 'Type' it expands -- into, and (possibly) a coercion from the representation type to the @newtype@. -- Returns @Nothing@ if this is not possible. unwrapNewTyCon_maybe :: TyCon -> Maybe ([TyVar], Type, CoAxiom Unbranched) unwrapNewTyCon_maybe (AlgTyCon { tyConTyVars = tvs, algTcRhs = NewTyCon { nt_co = co, nt_rhs = rhs }}) = Just (tvs, rhs, co) unwrapNewTyCon_maybe _ = Nothing unwrapNewTyConEtad_maybe :: TyCon -> Maybe ([TyVar], Type, CoAxiom Unbranched) unwrapNewTyConEtad_maybe (AlgTyCon { algTcRhs = NewTyCon { nt_co = co, nt_etad_rhs = (tvs,rhs) }}) = Just (tvs, rhs, co) unwrapNewTyConEtad_maybe _ = Nothing isProductTyCon :: TyCon -> Bool -- True of datatypes or newtypes that have -- one, non-existential, data constructor -- See Note [Product types] isProductTyCon tc@(AlgTyCon {}) = case algTcRhs tc of TupleTyCon {} -> True DataTyCon{ data_cons = [data_con] } -> null (dataConExTyVars data_con) NewTyCon {} -> True _ -> False isProductTyCon _ = False isDataProductTyCon_maybe :: TyCon -> Maybe DataCon -- True of datatypes (not newtypes) with -- one, vanilla, data constructor -- See Note [Product types] isDataProductTyCon_maybe (AlgTyCon { algTcRhs = rhs }) = case rhs of DataTyCon { data_cons = [con] } | null (dataConExTyVars con) -- non-existential -> Just con TupleTyCon { data_con = con } -> Just con _ -> Nothing isDataProductTyCon_maybe _ = Nothing isDataSumTyCon_maybe :: TyCon -> Maybe [DataCon] isDataSumTyCon_maybe (AlgTyCon { algTcRhs = rhs }) = case rhs of DataTyCon { data_cons = cons } | cons `lengthExceeds` 1 , all (null . dataConExTyVars) cons -- FIXME(osa): Why do we need this? -> Just cons SumTyCon { data_cons = cons } | all (null . dataConExTyVars) cons -- FIXME(osa): Why do we need this? -> Just cons _ -> Nothing isDataSumTyCon_maybe _ = Nothing {- Note [Product types] ~~~~~~~~~~~~~~~~~~~~~~~ A product type is * A data type (not a newtype) * With one, boxed data constructor * That binds no existential type variables The main point is that product types are amenable to unboxing for * Strict function calls; we can transform f (D a b) = e to fw a b = e via the worker/wrapper transformation. (Question: couldn't this work for existentials too?) * CPR for function results; we can transform f x y = let ... in D a b to fw x y = let ... in (# a, b #) Note that the data constructor /can/ have evidence arguments: equality constraints, type classes etc. So it can be GADT. These evidence arguments are simply value arguments, and should not get in the way. -} -- | Is this a 'TyCon' representing a regular H98 type synonym (@type@)? isTypeSynonymTyCon :: TyCon -> Bool isTypeSynonymTyCon (SynonymTyCon {}) = True isTypeSynonymTyCon _ = False isTauTyCon :: TyCon -> Bool isTauTyCon (SynonymTyCon { synIsTau = is_tau }) = is_tau isTauTyCon _ = True isFamFreeTyCon :: TyCon -> Bool isFamFreeTyCon (SynonymTyCon { synIsFamFree = fam_free }) = fam_free isFamFreeTyCon (FamilyTyCon { famTcFlav = flav }) = isDataFamFlav flav isFamFreeTyCon _ = True -- As for newtypes, it is in some contexts important to distinguish between -- closed synonyms and synonym families, as synonym families have no unique -- right hand side to which a synonym family application can expand. -- -- | True iff we can decompose (T a b c) into ((T a b) c) -- I.e. is it injective and generative w.r.t nominal equality? -- That is, if (T a b) ~N d e f, is it always the case that -- (T ~N d), (a ~N e) and (b ~N f)? -- Specifically NOT true of synonyms (open and otherwise) -- -- It'd be unusual to call mightBeUnsaturatedTyCon on a regular H98 -- type synonym, because you should probably have expanded it first -- But regardless, it's not decomposable mightBeUnsaturatedTyCon :: TyCon -> Bool mightBeUnsaturatedTyCon = tcFlavourCanBeUnsaturated . tyConFlavour -- | Is this an algebraic 'TyCon' declared with the GADT syntax? isGadtSyntaxTyCon :: TyCon -> Bool isGadtSyntaxTyCon (AlgTyCon { algTcGadtSyntax = res }) = res isGadtSyntaxTyCon _ = False -- | Is this an algebraic 'TyCon' which is just an enumeration of values? isEnumerationTyCon :: TyCon -> Bool -- See Note [Enumeration types] in TyCon isEnumerationTyCon (AlgTyCon { tyConArity = arity, algTcRhs = rhs }) = case rhs of DataTyCon { is_enum = res } -> res TupleTyCon {} -> arity == 0 _ -> False isEnumerationTyCon _ = False -- | Is this a 'TyCon', synonym or otherwise, that defines a family? isFamilyTyCon :: TyCon -> Bool isFamilyTyCon (FamilyTyCon {}) = True isFamilyTyCon _ = False -- | Is this a 'TyCon', synonym or otherwise, that defines a family with -- instances? isOpenFamilyTyCon :: TyCon -> Bool isOpenFamilyTyCon (FamilyTyCon {famTcFlav = flav }) | OpenSynFamilyTyCon <- flav = True | DataFamilyTyCon {} <- flav = True isOpenFamilyTyCon _ = False -- | Is this a synonym 'TyCon' that can have may have further instances appear? isTypeFamilyTyCon :: TyCon -> Bool isTypeFamilyTyCon (FamilyTyCon { famTcFlav = flav }) = not (isDataFamFlav flav) isTypeFamilyTyCon _ = False -- | Is this a synonym 'TyCon' that can have may have further instances appear? isDataFamilyTyCon :: TyCon -> Bool isDataFamilyTyCon (FamilyTyCon { famTcFlav = flav }) = isDataFamFlav flav isDataFamilyTyCon _ = False -- | Is this an open type family TyCon? isOpenTypeFamilyTyCon :: TyCon -> Bool isOpenTypeFamilyTyCon (FamilyTyCon {famTcFlav = OpenSynFamilyTyCon }) = True isOpenTypeFamilyTyCon _ = False -- | Is this a non-empty closed type family? Returns 'Nothing' for -- abstract or empty closed families. isClosedSynFamilyTyConWithAxiom_maybe :: TyCon -> Maybe (CoAxiom Branched) isClosedSynFamilyTyConWithAxiom_maybe (FamilyTyCon {famTcFlav = ClosedSynFamilyTyCon mb}) = mb isClosedSynFamilyTyConWithAxiom_maybe _ = Nothing -- | @'tyConInjectivityInfo' tc@ returns @'Injective' is@ is @tc@ is an -- injective tycon (where @is@ states for which 'tyConBinders' @tc@ is -- injective), or 'NotInjective' otherwise. tyConInjectivityInfo :: TyCon -> Injectivity tyConInjectivityInfo tc | FamilyTyCon { famTcInj = inj } <- tc = inj | isInjectiveTyCon tc Nominal = Injective (replicate (tyConArity tc) True) | otherwise = NotInjective isBuiltInSynFamTyCon_maybe :: TyCon -> Maybe BuiltInSynFamily isBuiltInSynFamTyCon_maybe (FamilyTyCon {famTcFlav = BuiltInSynFamTyCon ops }) = Just ops isBuiltInSynFamTyCon_maybe _ = Nothing isDataFamFlav :: FamTyConFlav -> Bool isDataFamFlav (DataFamilyTyCon {}) = True -- Data family isDataFamFlav _ = False -- Type synonym family -- | Are we able to extract information 'TyVar' to class argument list -- mapping from a given 'TyCon'? isTyConAssoc :: TyCon -> Bool isTyConAssoc tc = isJust (tyConAssoc_maybe tc) tyConAssoc_maybe :: TyCon -> Maybe Class tyConAssoc_maybe (FamilyTyCon { famTcParent = mb_cls }) = mb_cls tyConAssoc_maybe _ = Nothing -- The unit tycon didn't used to be classed as a tuple tycon -- but I thought that was silly so I've undone it -- If it can't be for some reason, it should be a AlgTyCon isTupleTyCon :: TyCon -> Bool -- ^ Does this 'TyCon' represent a tuple? -- -- NB: when compiling @Data.Tuple@, the tycons won't reply @True@ to -- 'isTupleTyCon', because they are built as 'AlgTyCons'. However they -- get spat into the interface file as tuple tycons, so I don't think -- it matters. isTupleTyCon (AlgTyCon { algTcRhs = TupleTyCon {} }) = True isTupleTyCon _ = False tyConTuple_maybe :: TyCon -> Maybe TupleSort tyConTuple_maybe (AlgTyCon { algTcRhs = rhs }) | TupleTyCon { tup_sort = sort} <- rhs = Just sort tyConTuple_maybe _ = Nothing -- | Is this the 'TyCon' for an unboxed tuple? isUnboxedTupleTyCon :: TyCon -> Bool isUnboxedTupleTyCon (AlgTyCon { algTcRhs = rhs }) | TupleTyCon { tup_sort = sort } <- rhs = not (isBoxed (tupleSortBoxity sort)) isUnboxedTupleTyCon _ = False -- | Is this the 'TyCon' for a boxed tuple? isBoxedTupleTyCon :: TyCon -> Bool isBoxedTupleTyCon (AlgTyCon { algTcRhs = rhs }) | TupleTyCon { tup_sort = sort } <- rhs = isBoxed (tupleSortBoxity sort) isBoxedTupleTyCon _ = False -- | Is this the 'TyCon' for an unboxed sum? isUnboxedSumTyCon :: TyCon -> Bool isUnboxedSumTyCon (AlgTyCon { algTcRhs = rhs }) | SumTyCon {} <- rhs = True isUnboxedSumTyCon _ = False -- | Is this the 'TyCon' for a /promoted/ tuple? isPromotedTupleTyCon :: TyCon -> Bool isPromotedTupleTyCon tyCon | Just dataCon <- isPromotedDataCon_maybe tyCon , isTupleTyCon (dataConTyCon dataCon) = True | otherwise = False -- | Is this a PromotedDataCon? isPromotedDataCon :: TyCon -> Bool isPromotedDataCon (PromotedDataCon {}) = True isPromotedDataCon _ = False -- | Retrieves the promoted DataCon if this is a PromotedDataCon; isPromotedDataCon_maybe :: TyCon -> Maybe DataCon isPromotedDataCon_maybe (PromotedDataCon { dataCon = dc }) = Just dc isPromotedDataCon_maybe _ = Nothing -- | Is this tycon really meant for use at the kind level? That is, -- should it be permitted without -XDataKinds? isKindTyCon :: TyCon -> Bool isKindTyCon tc = getUnique tc `elementOfUniqSet` kindTyConKeys -- | These TyCons should be allowed at the kind level, even without -- -XDataKinds. kindTyConKeys :: UniqSet Unique kindTyConKeys = unionManyUniqSets ( mkUniqSet [ liftedTypeKindTyConKey, constraintKindTyConKey, tYPETyConKey ] : map (mkUniqSet . tycon_with_datacons) [ runtimeRepTyCon , vecCountTyCon, vecElemTyCon ] ) where tycon_with_datacons tc = getUnique tc : map getUnique (tyConDataCons tc) isLiftedTypeKindTyConName :: Name -> Bool isLiftedTypeKindTyConName = (`hasKey` liftedTypeKindTyConKey) -- | Identifies implicit tycons that, in particular, do not go into interface -- files (because they are implicitly reconstructed when the interface is -- read). -- -- Note that: -- -- * Associated families are implicit, as they are re-constructed from -- the class declaration in which they reside, and -- -- * Family instances are /not/ implicit as they represent the instance body -- (similar to a @dfun@ does that for a class instance). -- -- * Tuples are implicit iff they have a wired-in name -- (namely: boxed and unboxed tupeles are wired-in and implicit, -- but constraint tuples are not) isImplicitTyCon :: TyCon -> Bool isImplicitTyCon (FunTyCon {}) = True isImplicitTyCon (PrimTyCon {}) = True isImplicitTyCon (PromotedDataCon {}) = True isImplicitTyCon (AlgTyCon { algTcRhs = rhs, tyConName = name }) | TupleTyCon {} <- rhs = isWiredInName name | SumTyCon {} <- rhs = True | otherwise = False isImplicitTyCon (FamilyTyCon { famTcParent = parent }) = isJust parent isImplicitTyCon (SynonymTyCon {}) = False isImplicitTyCon (TcTyCon {}) = False tyConCType_maybe :: TyCon -> Maybe CType tyConCType_maybe tc@(AlgTyCon {}) = tyConCType tc tyConCType_maybe _ = Nothing -- | Is this a TcTyCon? (That is, one only used during type-checking?) isTcTyCon :: TyCon -> Bool isTcTyCon (TcTyCon {}) = True isTcTyCon _ = False -- | Could this TyCon ever be levity-polymorphic when fully applied? -- True is safe. False means we're sure. Does only a quick check -- based on the TyCon's category. -- Precondition: The fully-applied TyCon has kind (TYPE blah) isTcLevPoly :: TyCon -> Bool isTcLevPoly FunTyCon{} = False isTcLevPoly (AlgTyCon { algTcParent = UnboxedAlgTyCon _ }) = True isTcLevPoly AlgTyCon{} = False isTcLevPoly SynonymTyCon{} = True isTcLevPoly FamilyTyCon{} = True isTcLevPoly PrimTyCon{} = False isTcLevPoly TcTyCon{} = False isTcLevPoly tc@PromotedDataCon{} = pprPanic "isTcLevPoly datacon" (ppr tc) {- ----------------------------------------------- -- Expand type-constructor applications ----------------------------------------------- -} expandSynTyCon_maybe :: TyCon -> [tyco] -- ^ Arguments to 'TyCon' -> Maybe ([(TyVar,tyco)], Type, [tyco]) -- ^ Returns a 'TyVar' substitution, the body -- type of the synonym (not yet substituted) -- and any arguments remaining from the -- application -- ^ Expand a type synonym application, if any expandSynTyCon_maybe tc tys | SynonymTyCon { tyConTyVars = tvs, synTcRhs = rhs, tyConArity = arity } <- tc = case tys `listLengthCmp` arity of GT -> Just (tvs `zip` tys, rhs, drop arity tys) EQ -> Just (tvs `zip` tys, rhs, []) LT -> Nothing | otherwise = Nothing ---------------- -- | Check if the tycon actually refers to a proper `data` or `newtype` -- with user defined constructors rather than one from a class or other -- construction. -- NB: This is only used in TcRnExports.checkPatSynParent to determine if an -- exported tycon can have a pattern synonym bundled with it, e.g., -- module Foo (TyCon(.., PatSyn)) where isTyConWithSrcDataCons :: TyCon -> Bool isTyConWithSrcDataCons (AlgTyCon { algTcRhs = rhs, algTcParent = parent }) = case rhs of DataTyCon {} -> isSrcParent NewTyCon {} -> isSrcParent TupleTyCon {} -> isSrcParent _ -> False where isSrcParent = isNoParent parent isTyConWithSrcDataCons (FamilyTyCon { famTcFlav = DataFamilyTyCon {} }) = True -- #14058 isTyConWithSrcDataCons _ = False -- | As 'tyConDataCons_maybe', but returns the empty list of constructors if no -- constructors could be found tyConDataCons :: TyCon -> [DataCon] -- It's convenient for tyConDataCons to return the -- empty list for type synonyms etc tyConDataCons tycon = tyConDataCons_maybe tycon `orElse` [] -- | Determine the 'DataCon's originating from the given 'TyCon', if the 'TyCon' -- is the sort that can have any constructors (note: this does not include -- abstract algebraic types) tyConDataCons_maybe :: TyCon -> Maybe [DataCon] tyConDataCons_maybe (AlgTyCon {algTcRhs = rhs}) = case rhs of DataTyCon { data_cons = cons } -> Just cons NewTyCon { data_con = con } -> Just [con] TupleTyCon { data_con = con } -> Just [con] SumTyCon { data_cons = cons } -> Just cons _ -> Nothing tyConDataCons_maybe _ = Nothing -- | If the given 'TyCon' has a /single/ data constructor, i.e. it is a @data@ -- type with one alternative, a tuple type or a @newtype@ then that constructor -- is returned. If the 'TyCon' has more than one constructor, or represents a -- primitive or function type constructor then @Nothing@ is returned. In any -- other case, the function panics tyConSingleDataCon_maybe :: TyCon -> Maybe DataCon tyConSingleDataCon_maybe (AlgTyCon { algTcRhs = rhs }) = case rhs of DataTyCon { data_cons = [c] } -> Just c TupleTyCon { data_con = c } -> Just c NewTyCon { data_con = c } -> Just c _ -> Nothing tyConSingleDataCon_maybe _ = Nothing tyConSingleDataCon :: TyCon -> DataCon tyConSingleDataCon tc = case tyConSingleDataCon_maybe tc of Just c -> c Nothing -> pprPanic "tyConDataCon" (ppr tc) tyConSingleAlgDataCon_maybe :: TyCon -> Maybe DataCon -- Returns (Just con) for single-constructor -- *algebraic* data types *not* newtypes tyConSingleAlgDataCon_maybe (AlgTyCon { algTcRhs = rhs }) = case rhs of DataTyCon { data_cons = [c] } -> Just c TupleTyCon { data_con = c } -> Just c _ -> Nothing tyConSingleAlgDataCon_maybe _ = Nothing -- | Determine the number of value constructors a 'TyCon' has. Panics if the -- 'TyCon' is not algebraic or a tuple tyConFamilySize :: TyCon -> Int tyConFamilySize tc@(AlgTyCon { algTcRhs = rhs }) = case rhs of DataTyCon { data_cons_size = size } -> size NewTyCon {} -> 1 TupleTyCon {} -> 1 SumTyCon { data_cons_size = size } -> size _ -> pprPanic "tyConFamilySize 1" (ppr tc) tyConFamilySize tc = pprPanic "tyConFamilySize 2" (ppr tc) -- | Extract an 'AlgTyConRhs' with information about data constructors from an -- algebraic or tuple 'TyCon'. Panics for any other sort of 'TyCon' algTyConRhs :: TyCon -> AlgTyConRhs algTyConRhs (AlgTyCon {algTcRhs = rhs}) = rhs algTyConRhs other = pprPanic "algTyConRhs" (ppr other) -- | Extract type variable naming the result of injective type family tyConFamilyResVar_maybe :: TyCon -> Maybe Name tyConFamilyResVar_maybe (FamilyTyCon {famTcResVar = res}) = res tyConFamilyResVar_maybe _ = Nothing -- | Get the list of roles for the type parameters of a TyCon tyConRoles :: TyCon -> [Role] -- See also Note [TyCon Role signatures] tyConRoles tc = case tc of { FunTyCon {} -> const_role Representational ; AlgTyCon { tcRoles = roles } -> roles ; SynonymTyCon { tcRoles = roles } -> roles ; FamilyTyCon {} -> const_role Nominal ; PrimTyCon { tcRoles = roles } -> roles ; PromotedDataCon { tcRoles = roles } -> roles ; TcTyCon {} -> const_role Nominal } where const_role r = replicate (tyConArity tc) r -- | Extract the bound type variables and type expansion of a type synonym -- 'TyCon'. Panics if the 'TyCon' is not a synonym newTyConRhs :: TyCon -> ([TyVar], Type) newTyConRhs (AlgTyCon {tyConTyVars = tvs, algTcRhs = NewTyCon { nt_rhs = rhs }}) = (tvs, rhs) newTyConRhs tycon = pprPanic "newTyConRhs" (ppr tycon) -- | The number of type parameters that need to be passed to a newtype to -- resolve it. May be less than in the definition if it can be eta-contracted. newTyConEtadArity :: TyCon -> Int newTyConEtadArity (AlgTyCon {algTcRhs = NewTyCon { nt_etad_rhs = tvs_rhs }}) = length (fst tvs_rhs) newTyConEtadArity tycon = pprPanic "newTyConEtadArity" (ppr tycon) -- | Extract the bound type variables and type expansion of an eta-contracted -- type synonym 'TyCon'. Panics if the 'TyCon' is not a synonym newTyConEtadRhs :: TyCon -> ([TyVar], Type) newTyConEtadRhs (AlgTyCon {algTcRhs = NewTyCon { nt_etad_rhs = tvs_rhs }}) = tvs_rhs newTyConEtadRhs tycon = pprPanic "newTyConEtadRhs" (ppr tycon) -- | Extracts the @newtype@ coercion from such a 'TyCon', which can be used to -- construct something with the @newtype@s type from its representation type -- (right hand side). If the supplied 'TyCon' is not a @newtype@, returns -- @Nothing@ newTyConCo_maybe :: TyCon -> Maybe (CoAxiom Unbranched) newTyConCo_maybe (AlgTyCon {algTcRhs = NewTyCon { nt_co = co }}) = Just co newTyConCo_maybe _ = Nothing newTyConCo :: TyCon -> CoAxiom Unbranched newTyConCo tc = case newTyConCo_maybe tc of Just co -> co Nothing -> pprPanic "newTyConCo" (ppr tc) newTyConDataCon_maybe :: TyCon -> Maybe DataCon newTyConDataCon_maybe (AlgTyCon {algTcRhs = NewTyCon { data_con = con }}) = Just con newTyConDataCon_maybe _ = Nothing -- | Find the \"stupid theta\" of the 'TyCon'. A \"stupid theta\" is the context -- to the left of an algebraic type declaration, e.g. @Eq a@ in the declaration -- @data Eq a => T a ...@ tyConStupidTheta :: TyCon -> [PredType] tyConStupidTheta (AlgTyCon {algTcStupidTheta = stupid}) = stupid tyConStupidTheta tycon = pprPanic "tyConStupidTheta" (ppr tycon) -- | Extract the 'TyVar's bound by a vanilla type synonym -- and the corresponding (unsubstituted) right hand side. synTyConDefn_maybe :: TyCon -> Maybe ([TyVar], Type) synTyConDefn_maybe (SynonymTyCon {tyConTyVars = tyvars, synTcRhs = ty}) = Just (tyvars, ty) synTyConDefn_maybe _ = Nothing -- | Extract the information pertaining to the right hand side of a type synonym -- (@type@) declaration. synTyConRhs_maybe :: TyCon -> Maybe Type synTyConRhs_maybe (SynonymTyCon {synTcRhs = rhs}) = Just rhs synTyConRhs_maybe _ = Nothing -- | Extract the flavour of a type family (with all the extra information that -- it carries) famTyConFlav_maybe :: TyCon -> Maybe FamTyConFlav famTyConFlav_maybe (FamilyTyCon {famTcFlav = flav}) = Just flav famTyConFlav_maybe _ = Nothing -- | Is this 'TyCon' that for a class instance? isClassTyCon :: TyCon -> Bool isClassTyCon (AlgTyCon {algTcParent = ClassTyCon {}}) = True isClassTyCon _ = False -- | If this 'TyCon' is that for a class instance, return the class it is for. -- Otherwise returns @Nothing@ tyConClass_maybe :: TyCon -> Maybe Class tyConClass_maybe (AlgTyCon {algTcParent = ClassTyCon clas _}) = Just clas tyConClass_maybe _ = Nothing -- | Return the associated types of the 'TyCon', if any tyConATs :: TyCon -> [TyCon] tyConATs (AlgTyCon {algTcParent = ClassTyCon clas _}) = classATs clas tyConATs _ = [] ---------------------------------------------------------------------------- -- | Is this 'TyCon' that for a data family instance? isFamInstTyCon :: TyCon -> Bool isFamInstTyCon (AlgTyCon {algTcParent = DataFamInstTyCon {} }) = True isFamInstTyCon _ = False tyConFamInstSig_maybe :: TyCon -> Maybe (TyCon, [Type], CoAxiom Unbranched) tyConFamInstSig_maybe (AlgTyCon {algTcParent = DataFamInstTyCon ax f ts }) = Just (f, ts, ax) tyConFamInstSig_maybe _ = Nothing -- | If this 'TyCon' is that of a data family instance, return the family in question -- and the instance types. Otherwise, return @Nothing@ tyConFamInst_maybe :: TyCon -> Maybe (TyCon, [Type]) tyConFamInst_maybe (AlgTyCon {algTcParent = DataFamInstTyCon _ f ts }) = Just (f, ts) tyConFamInst_maybe _ = Nothing -- | If this 'TyCon' is that of a data family instance, return a 'TyCon' which -- represents a coercion identifying the representation type with the type -- instance family. Otherwise, return @Nothing@ tyConFamilyCoercion_maybe :: TyCon -> Maybe (CoAxiom Unbranched) tyConFamilyCoercion_maybe (AlgTyCon {algTcParent = DataFamInstTyCon ax _ _ }) = Just ax tyConFamilyCoercion_maybe _ = Nothing -- | Extract any 'RuntimeRepInfo' from this TyCon tyConRuntimeRepInfo :: TyCon -> RuntimeRepInfo tyConRuntimeRepInfo (PromotedDataCon { promDcRepInfo = rri }) = rri tyConRuntimeRepInfo _ = NoRRI -- could panic in that second case. But Douglas Adams told me not to. {- Note [Constructor tag allocation] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ When typechecking we need to allocate constructor tags to constructors. They are allocated based on the position in the data_cons field of TyCon, with the first constructor getting fIRST_TAG. We used to pay linear cost per constructor, with each constructor looking up its relative index in the constructor list. That was quadratic and prohibitive for large data types with more than 10k constructors. The current strategy is to build a NameEnv with a mapping from costructor's Name to ConTag and pass it down to buildDataCon for efficient lookup. Relevant ticket: #14657 -} mkTyConTagMap :: TyCon -> NameEnv ConTag mkTyConTagMap tycon = mkNameEnv $ map getName (tyConDataCons tycon) `zip` [fIRST_TAG..] -- See Note [Constructor tag allocation] {- ************************************************************************ * * \subsection[TyCon-instances]{Instance declarations for @TyCon@} * * ************************************************************************ @TyCon@s are compared by comparing their @Unique@s. -} instance Eq TyCon where a == b = getUnique a == getUnique b a /= b = getUnique a /= getUnique b instance Uniquable TyCon where getUnique tc = tyConUnique tc instance Outputable TyCon where -- At the moment a promoted TyCon has the same Name as its -- corresponding TyCon, so we add the quote to distinguish it here ppr tc = pprPromotionQuote tc <> ppr (tyConName tc) <> pp_tc where pp_tc = getPprStyle $ \sty -> if ((debugStyle sty || dumpStyle sty) && isTcTyCon tc) then text "[tc]" else empty -- | Paints a picture of what a 'TyCon' represents, in broad strokes. -- This is used towards more informative error messages. data TyConFlavour = ClassFlavour | TupleFlavour Boxity | SumFlavour | DataTypeFlavour | NewtypeFlavour | AbstractTypeFlavour | DataFamilyFlavour Bool -- True <=> associated | OpenTypeFamilyFlavour Bool -- True <=> associated | ClosedTypeFamilyFlavour | TypeSynonymFlavour | BuiltInTypeFlavour -- ^ e.g., the @(->)@ 'TyCon'. | PromotedDataConFlavour deriving Eq instance Outputable TyConFlavour where ppr = text . go where go ClassFlavour = "class" go (TupleFlavour boxed) | isBoxed boxed = "tuple" | otherwise = "unboxed tuple" go SumFlavour = "unboxed sum" go DataTypeFlavour = "data type" go NewtypeFlavour = "newtype" go AbstractTypeFlavour = "abstract type" go (DataFamilyFlavour True) = "associated data family" go (DataFamilyFlavour False) = "data family" go (OpenTypeFamilyFlavour True) = "associated type family" go (OpenTypeFamilyFlavour False) = "type family" go ClosedTypeFamilyFlavour = "type family" go TypeSynonymFlavour = "type synonym" go BuiltInTypeFlavour = "built-in type" go PromotedDataConFlavour = "promoted data constructor" tyConFlavour :: TyCon -> TyConFlavour tyConFlavour (AlgTyCon { algTcParent = parent, algTcRhs = rhs }) | ClassTyCon _ _ <- parent = ClassFlavour | otherwise = case rhs of TupleTyCon { tup_sort = sort } -> TupleFlavour (tupleSortBoxity sort) SumTyCon {} -> SumFlavour DataTyCon {} -> DataTypeFlavour NewTyCon {} -> NewtypeFlavour AbstractTyCon {} -> AbstractTypeFlavour tyConFlavour (FamilyTyCon { famTcFlav = flav, famTcParent = parent }) = case flav of DataFamilyTyCon{} -> DataFamilyFlavour (isJust parent) OpenSynFamilyTyCon -> OpenTypeFamilyFlavour (isJust parent) ClosedSynFamilyTyCon{} -> ClosedTypeFamilyFlavour AbstractClosedSynFamilyTyCon -> ClosedTypeFamilyFlavour BuiltInSynFamTyCon{} -> ClosedTypeFamilyFlavour tyConFlavour (SynonymTyCon {}) = TypeSynonymFlavour tyConFlavour (FunTyCon {}) = BuiltInTypeFlavour tyConFlavour (PrimTyCon {}) = BuiltInTypeFlavour tyConFlavour (PromotedDataCon {}) = PromotedDataConFlavour tyConFlavour (TcTyCon { tcTyConFlavour = flav }) = flav -- | Can this flavour of 'TyCon' appear unsaturated? tcFlavourCanBeUnsaturated :: TyConFlavour -> Bool tcFlavourCanBeUnsaturated ClassFlavour = True tcFlavourCanBeUnsaturated DataTypeFlavour = True tcFlavourCanBeUnsaturated NewtypeFlavour = True tcFlavourCanBeUnsaturated DataFamilyFlavour{} = True tcFlavourCanBeUnsaturated TupleFlavour{} = True tcFlavourCanBeUnsaturated SumFlavour = True tcFlavourCanBeUnsaturated AbstractTypeFlavour = True tcFlavourCanBeUnsaturated BuiltInTypeFlavour = True tcFlavourCanBeUnsaturated PromotedDataConFlavour = True tcFlavourCanBeUnsaturated TypeSynonymFlavour = False tcFlavourCanBeUnsaturated OpenTypeFamilyFlavour{} = False tcFlavourCanBeUnsaturated ClosedTypeFamilyFlavour = False -- | Is this flavour of 'TyCon' an open type family or a data family? tcFlavourIsOpen :: TyConFlavour -> Bool tcFlavourIsOpen DataFamilyFlavour{} = True tcFlavourIsOpen OpenTypeFamilyFlavour{} = True tcFlavourIsOpen ClosedTypeFamilyFlavour = False tcFlavourIsOpen ClassFlavour = False tcFlavourIsOpen DataTypeFlavour = False tcFlavourIsOpen NewtypeFlavour = False tcFlavourIsOpen TupleFlavour{} = False tcFlavourIsOpen SumFlavour = False tcFlavourIsOpen AbstractTypeFlavour = False tcFlavourIsOpen BuiltInTypeFlavour = False tcFlavourIsOpen PromotedDataConFlavour = False tcFlavourIsOpen TypeSynonymFlavour = False pprPromotionQuote :: TyCon -> SDoc -- Promoted data constructors already have a tick in their OccName pprPromotionQuote tc = case tc of PromotedDataCon {} -> char '\'' -- Always quote promoted DataCons in types _ -> empty instance NamedThing TyCon where getName = tyConName instance Data.Data TyCon where -- don't traverse? toConstr _ = abstractConstr "TyCon" gunfold _ _ = error "gunfold" dataTypeOf _ = mkNoRepType "TyCon" instance Binary Injectivity where put_ bh NotInjective = putByte bh 0 put_ bh (Injective xs) = putByte bh 1 >> put_ bh xs get bh = do { h <- getByte bh ; case h of 0 -> return NotInjective _ -> do { xs <- get bh ; return (Injective xs) } } {- ************************************************************************ * * Walking over recursive TyCons * * ************************************************************************ Note [Expanding newtypes and products] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ When expanding a type to expose a data-type constructor, we need to be careful about newtypes, lest we fall into an infinite loop. Here are the key examples: newtype Id x = MkId x newtype Fix f = MkFix (f (Fix f)) newtype T = MkT (T -> T) Type Expansion -------------------------- T T -> T Fix Maybe Maybe (Fix Maybe) Id (Id Int) Int Fix Id NO NO NO Notice that * We can expand T, even though it's recursive. * We can expand Id (Id Int), even though the Id shows up twice at the outer level, because Id is non-recursive So, when expanding, we keep track of when we've seen a recursive newtype at outermost level; and bail out if we see it again. We sometimes want to do the same for product types, so that the strictness analyser doesn't unbox infinitely deeply. More precisely, we keep a *count* of how many times we've seen it. This is to account for data instance T (a,b) = MkT (T a) (T b) Then (Trac #10482) if we have a type like T (Int,(Int,(Int,(Int,Int)))) we can still unbox deeply enough during strictness analysis. We have to treat T as potentially recursive, but it's still good to be able to unwrap multiple layers. The function that manages all this is checkRecTc. -} data RecTcChecker = RC !Int (NameEnv Int) -- The upper bound, and the number of times -- we have encountered each TyCon initRecTc :: RecTcChecker -- Initialise with a fixed max bound of 100 -- We should probably have a flag for this initRecTc = RC 100 emptyNameEnv checkRecTc :: RecTcChecker -> TyCon -> Maybe RecTcChecker -- Nothing => Recursion detected -- Just rec_tcs => Keep going checkRecTc (RC bound rec_nts) tc = case lookupNameEnv rec_nts tc_name of Just n | n >= bound -> Nothing | otherwise -> Just (RC bound (extendNameEnv rec_nts tc_name (n+1))) Nothing -> Just (RC bound (extendNameEnv rec_nts tc_name 1)) where tc_name = tyConName tc -- | Returns whether or not this 'TyCon' is definite, or a hole -- that may be filled in at some later point. See Note [Skolem abstract data] tyConSkolem :: TyCon -> Bool tyConSkolem = isHoleName . tyConName -- Note [Skolem abstract data] -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~ -- Skolem abstract data arises from data declarations in an hsig file. -- -- The best analogy is to interpret the types declared in signature files as -- elaborating to universally quantified type variables; e.g., -- -- unit p where -- signature H where -- data T -- data S -- module M where -- import H -- f :: (T ~ S) => a -> b -- f x = x -- -- elaborates as (with some fake structural types): -- -- p :: forall t s. { f :: forall a b. t ~ s => a -> b } -- p = { f = \x -> x } -- ill-typed -- -- It is clear that inside p, t ~ s is not provable (and -- if we tried to write a function to cast t to s, that -- would not work), but if we call p @Int @Int, clearly Int ~ Int -- is provable. The skolem variables are all distinct from -- one another, but we can't make assumptions like "f is -- inaccessible", because the skolem variables will get -- instantiated eventually! -- -- Skolem abstractness can apply to "non-abstract" data as well): -- -- unit p where -- signature H1 where -- data T = MkT -- signature H2 where -- data T = MkT -- module M where -- import qualified H1 -- import qualified H2 -- f :: (H1.T ~ H2.T) => a -> b -- f x = x -- -- This is why the test is on the original name of the TyCon, -- not whether it is abstract or not.