% % (c) The AQUA Project, Glasgow University, 1994-1998 % \section[TysPrim]{Wired-in knowledge about primitive types} \begin{code} -- | This module defines TyCons that can't be expressed in Haskell. -- They are all, therefore, wired-in TyCons. C.f module TysWiredIn module TysPrim( mkPrimTyConName, -- For implicit parameters in TysWiredIn only tyVarList, alphaTyVars, betaTyVars, alphaTyVar, betaTyVar, gammaTyVar, deltaTyVar, alphaTy, betaTy, gammaTy, deltaTy, openAlphaTy, openBetaTy, openAlphaTyVar, openBetaTyVar, openAlphaTyVars, argAlphaTy, argAlphaTyVar, argBetaTy, argBetaTyVar, -- Kind constructors... tySuperKindTyCon, tySuperKind, liftedTypeKindTyCon, openTypeKindTyCon, unliftedTypeKindTyCon, argTypeKindTyCon, ubxTupleKindTyCon, constraintKindTyCon, tySuperKindTyConName, liftedTypeKindTyConName, openTypeKindTyConName, unliftedTypeKindTyConName, ubxTupleKindTyConName, argTypeKindTyConName, constraintKindTyConName, -- Kinds liftedTypeKind, unliftedTypeKind, openTypeKind, argTypeKind, ubxTupleKind, constraintKind, mkArrowKind, mkArrowKinds, funTyCon, funTyConName, primTyCons, charPrimTyCon, charPrimTy, intPrimTyCon, intPrimTy, wordPrimTyCon, wordPrimTy, addrPrimTyCon, addrPrimTy, floatPrimTyCon, floatPrimTy, doublePrimTyCon, doublePrimTy, statePrimTyCon, mkStatePrimTy, realWorldTyCon, realWorldTy, realWorldStatePrimTy, arrayPrimTyCon, mkArrayPrimTy, byteArrayPrimTyCon, byteArrayPrimTy, mutableArrayPrimTyCon, mkMutableArrayPrimTy, mutableByteArrayPrimTyCon, mkMutableByteArrayPrimTy, mutVarPrimTyCon, mkMutVarPrimTy, mVarPrimTyCon, mkMVarPrimTy, tVarPrimTyCon, mkTVarPrimTy, stablePtrPrimTyCon, mkStablePtrPrimTy, stableNamePrimTyCon, mkStableNamePrimTy, bcoPrimTyCon, bcoPrimTy, weakPrimTyCon, mkWeakPrimTy, threadIdPrimTyCon, threadIdPrimTy, int32PrimTyCon, int32PrimTy, word32PrimTyCon, word32PrimTy, int64PrimTyCon, int64PrimTy, word64PrimTyCon, word64PrimTy, eqPrimTyCon, -- ty1 ~# ty2 -- * Any anyTy, anyTyCon, anyTyConOfKind, anyTypeOfKind ) where #include "HsVersions.h" import Var ( TyVar, mkTyVar ) import Name ( Name, BuiltInSyntax(..), mkInternalName, mkWiredInName ) import OccName ( mkTcOcc,mkTyVarOccFS, mkTcOccFS ) import TyCon import TypeRep import SrcLoc import Unique ( mkAlphaTyVarUnique ) import PrelNames import FastString import Outputable import Data.Char \end{code} %************************************************************************ %* * \subsection{Primitive type constructors} %* * %************************************************************************ \begin{code} primTyCons :: [TyCon] primTyCons = [ addrPrimTyCon , arrayPrimTyCon , byteArrayPrimTyCon , charPrimTyCon , doublePrimTyCon , floatPrimTyCon , intPrimTyCon , int32PrimTyCon , int64PrimTyCon , bcoPrimTyCon , weakPrimTyCon , mutableArrayPrimTyCon , mutableByteArrayPrimTyCon , mVarPrimTyCon , tVarPrimTyCon , mutVarPrimTyCon , realWorldTyCon , stablePtrPrimTyCon , stableNamePrimTyCon , statePrimTyCon , threadIdPrimTyCon , wordPrimTyCon , word32PrimTyCon , word64PrimTyCon , anyTyCon , eqPrimTyCon , liftedTypeKindTyCon , unliftedTypeKindTyCon , openTypeKindTyCon , argTypeKindTyCon , ubxTupleKindTyCon , constraintKindTyCon ] mkPrimTc :: FastString -> Unique -> TyCon -> Name mkPrimTc fs unique tycon = mkWiredInName gHC_PRIM (mkTcOccFS fs) unique (ATyCon tycon) -- Relevant TyCon UserSyntax -- None are built-in syntax charPrimTyConName, intPrimTyConName, int32PrimTyConName, int64PrimTyConName, wordPrimTyConName, word32PrimTyConName, word64PrimTyConName, addrPrimTyConName, floatPrimTyConName, doublePrimTyConName, statePrimTyConName, realWorldTyConName, arrayPrimTyConName, byteArrayPrimTyConName, mutableArrayPrimTyConName, mutableByteArrayPrimTyConName, mutVarPrimTyConName, mVarPrimTyConName, tVarPrimTyConName, stablePtrPrimTyConName, stableNamePrimTyConName, bcoPrimTyConName, weakPrimTyConName, threadIdPrimTyConName, eqPrimTyConName :: Name charPrimTyConName = mkPrimTc (fsLit "Char#") charPrimTyConKey charPrimTyCon intPrimTyConName = mkPrimTc (fsLit "Int#") intPrimTyConKey intPrimTyCon int32PrimTyConName = mkPrimTc (fsLit "Int32#") int32PrimTyConKey int32PrimTyCon int64PrimTyConName = mkPrimTc (fsLit "Int64#") int64PrimTyConKey int64PrimTyCon wordPrimTyConName = mkPrimTc (fsLit "Word#") wordPrimTyConKey wordPrimTyCon word32PrimTyConName = mkPrimTc (fsLit "Word32#") word32PrimTyConKey word32PrimTyCon word64PrimTyConName = mkPrimTc (fsLit "Word64#") word64PrimTyConKey word64PrimTyCon addrPrimTyConName = mkPrimTc (fsLit "Addr#") addrPrimTyConKey addrPrimTyCon floatPrimTyConName = mkPrimTc (fsLit "Float#") floatPrimTyConKey floatPrimTyCon doublePrimTyConName = mkPrimTc (fsLit "Double#") doublePrimTyConKey doublePrimTyCon statePrimTyConName = mkPrimTc (fsLit "State#") statePrimTyConKey statePrimTyCon eqPrimTyConName = mkPrimTc (fsLit "~#") eqPrimTyConKey eqPrimTyCon realWorldTyConName = mkPrimTc (fsLit "RealWorld") realWorldTyConKey realWorldTyCon arrayPrimTyConName = mkPrimTc (fsLit "Array#") arrayPrimTyConKey arrayPrimTyCon byteArrayPrimTyConName = mkPrimTc (fsLit "ByteArray#") byteArrayPrimTyConKey byteArrayPrimTyCon mutableArrayPrimTyConName = mkPrimTc (fsLit "MutableArray#") mutableArrayPrimTyConKey mutableArrayPrimTyCon mutableByteArrayPrimTyConName = mkPrimTc (fsLit "MutableByteArray#") mutableByteArrayPrimTyConKey mutableByteArrayPrimTyCon mutVarPrimTyConName = mkPrimTc (fsLit "MutVar#") mutVarPrimTyConKey mutVarPrimTyCon mVarPrimTyConName = mkPrimTc (fsLit "MVar#") mVarPrimTyConKey mVarPrimTyCon tVarPrimTyConName = mkPrimTc (fsLit "TVar#") tVarPrimTyConKey tVarPrimTyCon stablePtrPrimTyConName = mkPrimTc (fsLit "StablePtr#") stablePtrPrimTyConKey stablePtrPrimTyCon stableNamePrimTyConName = mkPrimTc (fsLit "StableName#") stableNamePrimTyConKey stableNamePrimTyCon bcoPrimTyConName = mkPrimTc (fsLit "BCO#") bcoPrimTyConKey bcoPrimTyCon weakPrimTyConName = mkPrimTc (fsLit "Weak#") weakPrimTyConKey weakPrimTyCon threadIdPrimTyConName = mkPrimTc (fsLit "ThreadId#") threadIdPrimTyConKey threadIdPrimTyCon \end{code} %************************************************************************ %* * \subsection{Support code} %* * %************************************************************************ alphaTyVars is a list of type variables for use in templates: ["a", "b", ..., "z", "t1", "t2", ... ] \begin{code} tyVarList :: Kind -> [TyVar] tyVarList kind = [ mkTyVar (mkInternalName (mkAlphaTyVarUnique u) (mkTyVarOccFS (mkFastString name)) noSrcSpan) kind | u <- [2..], let name | c <= 'z' = [c] | otherwise = 't':show u where c = chr (u-2 + ord 'a') ] alphaTyVars :: [TyVar] alphaTyVars = tyVarList liftedTypeKind betaTyVars :: [TyVar] betaTyVars = tail alphaTyVars alphaTyVar, betaTyVar, gammaTyVar, deltaTyVar :: TyVar (alphaTyVar:betaTyVar:gammaTyVar:deltaTyVar:_) = alphaTyVars alphaTys :: [Type] alphaTys = mkTyVarTys alphaTyVars alphaTy, betaTy, gammaTy, deltaTy :: Type (alphaTy:betaTy:gammaTy:deltaTy:_) = alphaTys -- openAlphaTyVar is prepared to be instantiated -- to a lifted or unlifted type variable. It's used for the -- result type for "error", so that we can have (error Int# "Help") openAlphaTyVars :: [TyVar] openAlphaTyVar, openBetaTyVar :: TyVar openAlphaTyVars@(openAlphaTyVar:openBetaTyVar:_) = tyVarList openTypeKind openAlphaTy, openBetaTy :: Type openAlphaTy = mkTyVarTy openAlphaTyVar openBetaTy = mkTyVarTy openBetaTyVar argAlphaTyVar, argBetaTyVar :: TyVar (argAlphaTyVar : argBetaTyVar : _) = tyVarList argTypeKind argAlphaTy, argBetaTy :: Type argAlphaTy = mkTyVarTy argAlphaTyVar argBetaTy = mkTyVarTy argBetaTyVar \end{code} %************************************************************************ %* * FunTyCon %* * %************************************************************************ \begin{code} funTyConName :: Name funTyConName = mkPrimTyConName (fsLit "(->)") funTyConKey funTyCon funTyCon :: TyCon funTyCon = mkFunTyCon funTyConName (mkArrowKinds [argTypeKind, openTypeKind] liftedTypeKind) -- You might think that (->) should have type (?? -> ? -> *), and you'd be right -- But if we do that we get kind errors when saying -- instance Control.Arrow (->) -- becuase the expected kind is (*->*->*). The trouble is that the -- expected/actual stuff in the unifier does not go contra-variant, whereas -- the kind sub-typing does. Sigh. It really only matters if you use (->) in -- a prefix way, thus: (->) Int# Int#. And this is unusual. -- because they are never in scope in the source \end{code} %************************************************************************ %* * Kinds %* * %************************************************************************ \begin{code} -- | See "Type#kind_subtyping" for details of the distinction between the 'Kind' 'TyCon's tySuperKindTyCon, liftedTypeKindTyCon, openTypeKindTyCon, unliftedTypeKindTyCon, ubxTupleKindTyCon, argTypeKindTyCon, constraintKindTyCon :: TyCon tySuperKindTyConName, liftedTypeKindTyConName, openTypeKindTyConName, unliftedTypeKindTyConName, ubxTupleKindTyConName, argTypeKindTyConName, constraintKindTyConName :: Name tySuperKindTyCon = mkSuperKindTyCon tySuperKindTyConName liftedTypeKindTyCon = mkKindTyCon liftedTypeKindTyConName tySuperKind openTypeKindTyCon = mkKindTyCon openTypeKindTyConName tySuperKind unliftedTypeKindTyCon = mkKindTyCon unliftedTypeKindTyConName tySuperKind ubxTupleKindTyCon = mkKindTyCon ubxTupleKindTyConName tySuperKind argTypeKindTyCon = mkKindTyCon argTypeKindTyConName tySuperKind constraintKindTyCon = mkKindTyCon constraintKindTyConName tySuperKind -------------------------- -- ... and now their names tySuperKindTyConName = mkPrimTyConName (fsLit "BOX") tySuperKindTyConKey tySuperKindTyCon liftedTypeKindTyConName = mkPrimTyConName (fsLit "*") liftedTypeKindTyConKey liftedTypeKindTyCon openTypeKindTyConName = mkPrimTyConName (fsLit "?") openTypeKindTyConKey openTypeKindTyCon unliftedTypeKindTyConName = mkPrimTyConName (fsLit "#") unliftedTypeKindTyConKey unliftedTypeKindTyCon ubxTupleKindTyConName = mkPrimTyConName (fsLit "(#)") ubxTupleKindTyConKey ubxTupleKindTyCon argTypeKindTyConName = mkPrimTyConName (fsLit "??") argTypeKindTyConKey argTypeKindTyCon constraintKindTyConName = mkPrimTyConName (fsLit "Constraint") constraintKindTyConKey constraintKindTyCon mkPrimTyConName :: FastString -> Unique -> TyCon -> Name mkPrimTyConName occ key tycon = mkWiredInName gHC_PRIM (mkTcOccFS occ) key (ATyCon tycon) BuiltInSyntax -- All of the super kinds and kinds are defined in Prim and use BuiltInSyntax, -- because they are never in scope in the source \end{code} \begin{code} kindTyConType :: TyCon -> Type kindTyConType kind = TyConApp kind [] -- | See "Type#kind_subtyping" for details of the distinction between these 'Kind's liftedTypeKind, unliftedTypeKind, openTypeKind, argTypeKind, ubxTupleKind, constraintKind :: Kind liftedTypeKind = kindTyConType liftedTypeKindTyCon unliftedTypeKind = kindTyConType unliftedTypeKindTyCon openTypeKind = kindTyConType openTypeKindTyCon argTypeKind = kindTyConType argTypeKindTyCon ubxTupleKind = kindTyConType ubxTupleKindTyCon constraintKind = kindTyConType constraintKindTyCon -- | Given two kinds @k1@ and @k2@, creates the 'Kind' @k1 -> k2@ mkArrowKind :: Kind -> Kind -> Kind mkArrowKind k1 k2 = FunTy k1 k2 -- | Iterated application of 'mkArrowKind' mkArrowKinds :: [Kind] -> Kind -> Kind mkArrowKinds arg_kinds result_kind = foldr mkArrowKind result_kind arg_kinds tySuperKind :: SuperKind tySuperKind = kindTyConType tySuperKindTyCon \end{code} %************************************************************************ %* * \subsection[TysPrim-basic]{Basic primitive types (@Char#@, @Int#@, etc.)} %* * %************************************************************************ \begin{code} -- only used herein pcPrimTyCon :: Name -> Int -> PrimRep -> TyCon pcPrimTyCon name arity rep = mkPrimTyCon name kind arity rep where kind = mkArrowKinds (replicate arity liftedTypeKind) result_kind result_kind = unliftedTypeKind pcPrimTyCon0 :: Name -> PrimRep -> TyCon pcPrimTyCon0 name rep = mkPrimTyCon name result_kind 0 rep where result_kind = unliftedTypeKind charPrimTy :: Type charPrimTy = mkTyConTy charPrimTyCon charPrimTyCon :: TyCon charPrimTyCon = pcPrimTyCon0 charPrimTyConName WordRep intPrimTy :: Type intPrimTy = mkTyConTy intPrimTyCon intPrimTyCon :: TyCon intPrimTyCon = pcPrimTyCon0 intPrimTyConName IntRep int32PrimTy :: Type int32PrimTy = mkTyConTy int32PrimTyCon int32PrimTyCon :: TyCon int32PrimTyCon = pcPrimTyCon0 int32PrimTyConName IntRep int64PrimTy :: Type int64PrimTy = mkTyConTy int64PrimTyCon int64PrimTyCon :: TyCon int64PrimTyCon = pcPrimTyCon0 int64PrimTyConName Int64Rep wordPrimTy :: Type wordPrimTy = mkTyConTy wordPrimTyCon wordPrimTyCon :: TyCon wordPrimTyCon = pcPrimTyCon0 wordPrimTyConName WordRep word32PrimTy :: Type word32PrimTy = mkTyConTy word32PrimTyCon word32PrimTyCon :: TyCon word32PrimTyCon = pcPrimTyCon0 word32PrimTyConName WordRep word64PrimTy :: Type word64PrimTy = mkTyConTy word64PrimTyCon word64PrimTyCon :: TyCon word64PrimTyCon = pcPrimTyCon0 word64PrimTyConName Word64Rep addrPrimTy :: Type addrPrimTy = mkTyConTy addrPrimTyCon addrPrimTyCon :: TyCon addrPrimTyCon = pcPrimTyCon0 addrPrimTyConName AddrRep floatPrimTy :: Type floatPrimTy = mkTyConTy floatPrimTyCon floatPrimTyCon :: TyCon floatPrimTyCon = pcPrimTyCon0 floatPrimTyConName FloatRep doublePrimTy :: Type doublePrimTy = mkTyConTy doublePrimTyCon doublePrimTyCon :: TyCon doublePrimTyCon = pcPrimTyCon0 doublePrimTyConName DoubleRep \end{code} %************************************************************************ %* * \subsection[TysPrim-state]{The @State#@ type (and @_RealWorld@ types)} %* * %************************************************************************ Note [The ~# TyCon) ~~~~~~~~~~~~~~~~~~~~ There is a perfectly ordinary type constructor ~# that represents the type of coercions (which, remember, are values). For example Refl Int :: ~# Int Int Atcually it is not quite "perfectly ordinary" because it is kind-polymorphic: Refl Maybe :: ~# Maybe Maybe So the true kind of ~# :: forall k. k -> k -> #. But we don't have polymorphic kinds (yet). However, (~) really only appears saturated in which case there is no problem in finding the kind of (ty1 ~# ty2). So we check that in CoreLint (and, in an assertion, in Kind.typeKind). Note [The State# TyCon] ~~~~~~~~~~~~~~~~~~~~~~~ State# is the primitive, unlifted type of states. It has one type parameter, thus State# RealWorld or State# s where s is a type variable. The only purpose of the type parameter is to keep different state threads separate. It is represented by nothing at all. \begin{code} mkStatePrimTy :: Type -> Type mkStatePrimTy ty = mkTyConApp statePrimTyCon [ty] statePrimTyCon :: TyCon -- See Note [The State# TyCon] statePrimTyCon = pcPrimTyCon statePrimTyConName 1 VoidRep eqPrimTyCon :: TyCon -- The representation type for equality predicates -- See Note [The ~# TyCon] eqPrimTyCon = pcPrimTyCon eqPrimTyConName 2 VoidRep \end{code} RealWorld is deeply magical. It is *primitive*, but it is not *unlifted* (hence ptrArg). We never manipulate values of type RealWorld; it's only used in the type system, to parameterise State#. \begin{code} realWorldTyCon :: TyCon realWorldTyCon = mkLiftedPrimTyCon realWorldTyConName liftedTypeKind 0 PtrRep realWorldTy :: Type realWorldTy = mkTyConTy realWorldTyCon realWorldStatePrimTy :: Type realWorldStatePrimTy = mkStatePrimTy realWorldTy -- State# RealWorld \end{code} Note: the ``state-pairing'' types are not truly primitive, so they are defined in \tr{TysWiredIn.lhs}, not here. %************************************************************************ %* * \subsection[TysPrim-arrays]{The primitive array types} %* * %************************************************************************ \begin{code} arrayPrimTyCon, mutableArrayPrimTyCon, mutableByteArrayPrimTyCon, byteArrayPrimTyCon :: TyCon arrayPrimTyCon = pcPrimTyCon arrayPrimTyConName 1 PtrRep mutableArrayPrimTyCon = pcPrimTyCon mutableArrayPrimTyConName 2 PtrRep mutableByteArrayPrimTyCon = pcPrimTyCon mutableByteArrayPrimTyConName 1 PtrRep byteArrayPrimTyCon = pcPrimTyCon0 byteArrayPrimTyConName PtrRep mkArrayPrimTy :: Type -> Type mkArrayPrimTy elt = mkTyConApp arrayPrimTyCon [elt] byteArrayPrimTy :: Type byteArrayPrimTy = mkTyConTy byteArrayPrimTyCon mkMutableArrayPrimTy :: Type -> Type -> Type mkMutableArrayPrimTy s elt = mkTyConApp mutableArrayPrimTyCon [s, elt] mkMutableByteArrayPrimTy :: Type -> Type mkMutableByteArrayPrimTy s = mkTyConApp mutableByteArrayPrimTyCon [s] \end{code} %************************************************************************ %* * \subsection[TysPrim-mut-var]{The mutable variable type} %* * %************************************************************************ \begin{code} mutVarPrimTyCon :: TyCon mutVarPrimTyCon = pcPrimTyCon mutVarPrimTyConName 2 PtrRep mkMutVarPrimTy :: Type -> Type -> Type mkMutVarPrimTy s elt = mkTyConApp mutVarPrimTyCon [s, elt] \end{code} %************************************************************************ %* * \subsection[TysPrim-synch-var]{The synchronizing variable type} %* * %************************************************************************ \begin{code} mVarPrimTyCon :: TyCon mVarPrimTyCon = pcPrimTyCon mVarPrimTyConName 2 PtrRep mkMVarPrimTy :: Type -> Type -> Type mkMVarPrimTy s elt = mkTyConApp mVarPrimTyCon [s, elt] \end{code} %************************************************************************ %* * \subsection[TysPrim-stm-var]{The transactional variable type} %* * %************************************************************************ \begin{code} tVarPrimTyCon :: TyCon tVarPrimTyCon = pcPrimTyCon tVarPrimTyConName 2 PtrRep mkTVarPrimTy :: Type -> Type -> Type mkTVarPrimTy s elt = mkTyConApp tVarPrimTyCon [s, elt] \end{code} %************************************************************************ %* * \subsection[TysPrim-stable-ptrs]{The stable-pointer type} %* * %************************************************************************ \begin{code} stablePtrPrimTyCon :: TyCon stablePtrPrimTyCon = pcPrimTyCon stablePtrPrimTyConName 1 AddrRep mkStablePtrPrimTy :: Type -> Type mkStablePtrPrimTy ty = mkTyConApp stablePtrPrimTyCon [ty] \end{code} %************************************************************************ %* * \subsection[TysPrim-stable-names]{The stable-name type} %* * %************************************************************************ \begin{code} stableNamePrimTyCon :: TyCon stableNamePrimTyCon = pcPrimTyCon stableNamePrimTyConName 1 PtrRep mkStableNamePrimTy :: Type -> Type mkStableNamePrimTy ty = mkTyConApp stableNamePrimTyCon [ty] \end{code} %************************************************************************ %* * \subsection[TysPrim-BCOs]{The ``bytecode object'' type} %* * %************************************************************************ \begin{code} bcoPrimTy :: Type bcoPrimTy = mkTyConTy bcoPrimTyCon bcoPrimTyCon :: TyCon bcoPrimTyCon = pcPrimTyCon0 bcoPrimTyConName PtrRep \end{code} %************************************************************************ %* * \subsection[TysPrim-Weak]{The ``weak pointer'' type} %* * %************************************************************************ \begin{code} weakPrimTyCon :: TyCon weakPrimTyCon = pcPrimTyCon weakPrimTyConName 1 PtrRep mkWeakPrimTy :: Type -> Type mkWeakPrimTy v = mkTyConApp weakPrimTyCon [v] \end{code} %************************************************************************ %* * \subsection[TysPrim-thread-ids]{The ``thread id'' type} %* * %************************************************************************ A thread id is represented by a pointer to the TSO itself, to ensure that they are always unique and we can always find the TSO for a given thread id. However, this has the unfortunate consequence that a ThreadId# for a given thread is treated as a root by the garbage collector and can keep TSOs around for too long. Hence the programmer API for thread manipulation uses a weak pointer to the thread id internally. \begin{code} threadIdPrimTy :: Type threadIdPrimTy = mkTyConTy threadIdPrimTyCon threadIdPrimTyCon :: TyCon threadIdPrimTyCon = pcPrimTyCon0 threadIdPrimTyConName PtrRep \end{code} %************************************************************************ %* * Any %* * %************************************************************************ Note [Any types] ~~~~~~~~~~~~~~~~ The type constructor Any::* has these properties * It is defined in module GHC.Prim, and exported so that it is available to users. For this reason it's treated like any other primitive type: - has a fixed unique, anyTyConKey, - lives in the global name cache - built with TyCon.PrimTyCon * It is lifted, and hence represented by a pointer * It is inhabited by at least one value, namely bottom * You can unsafely coerce any lifted type to Any, and back. * It does not claim to be a *data* type, and that's important for the code generator, because the code gen may *enter* a data value but never enters a function value. * It is used to instantiate otherwise un-constrained type variables of kind * For example length Any [] See Note [Strangely-kinded void TyCons] In addition, we have a potentially-infinite family of types, one for each kind /other than/ *, needed to instantiate otherwise un-constrained type variables of kinds other than *. This is a bit like tuples; there is a potentially-infinite family. They have slightly different characteristics to Any::*: * They are built with TyCon.AnyTyCon * They have non-user-writable names like "Any(*->*)" * They are not exported by GHC.Prim * They are uninhabited (of course; not kind *) * They have a unique derived from their OccName (see Note [Uniques of Any]) * Their Names do not live in the global name cache Note [Uniques of Any] ~~~~~~~~~~~~~~~~~~~~~ Although Any(*->*), say, doesn't have a binding site, it still needs to have a Unique. Unlike tuples (which are also an infinite family) there is no convenient way to index them, so we use the Unique from their OccName instead. That should be unique, - both wrt each other, because their strings differ - and wrt any other Name, because Names get uniques with various 'char' tags, but the OccName of Any will get a Unique built with mkTcOccUnique, which has a particular 'char' tag; see Unique.mkTcOccUnique! Note [Strangely-kinded void TyCons] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ See Trac #959 for more examples When the type checker finds a type variable with no binding, which means it can be instantiated with an arbitrary type, it usually instantiates it to Void. Eg. length [] ===> length Any (Nil Any) But in really obscure programs, the type variable might have a kind other than *, so we need to invent a suitably-kinded type. This commit uses Any for kind * Any(*->*) for kind *->* etc \begin{code} anyTyConName :: Name anyTyConName = mkPrimTc (fsLit "Any") anyTyConKey anyTyCon anyTy :: Type anyTy = mkTyConTy anyTyCon anyTyCon :: TyCon anyTyCon = mkLiftedPrimTyCon anyTyConName liftedTypeKind 0 PtrRep anyTypeOfKind :: Kind -> Type anyTypeOfKind kind = mkTyConApp (anyTyConOfKind kind) [] anyTyConOfKind :: Kind -> TyCon -- Map all superkinds of liftedTypeKind to liftedTypeKind anyTyConOfKind kind | isLiftedTypeKind kind = anyTyCon | otherwise = tycon where -- Derive the name from the kind, thus: -- Any(*->*), Any(*->*->*) -- These are names that can't be written by the user, -- and are not allocated in the global name cache str = "Any" ++ showSDoc (pprParendKind kind) occ = mkTcOcc str uniq = getUnique occ -- See Note [Uniques of Any] name = mkWiredInName gHC_PRIM occ uniq (ATyCon tycon) UserSyntax tycon = mkAnyTyCon name kind \end{code}