diff options
Diffstat (limited to 'compiler/prelude/TysPrim.hs')
| -rw-r--r-- | compiler/prelude/TysPrim.hs | 89 |
1 files changed, 54 insertions, 35 deletions
diff --git a/compiler/prelude/TysPrim.hs b/compiler/prelude/TysPrim.hs index 0732b5636d..c5af4a5121 100644 --- a/compiler/prelude/TysPrim.hs +++ b/compiler/prelude/TysPrim.hs @@ -30,7 +30,7 @@ module TysPrim( tYPE, primRepToRuntimeRep, funTyCon, funTyConName, - primTyCons, + unexposedPrimTyCons, exposedPrimTyCons, primTyCons, charPrimTyCon, charPrimTy, charPrimTyConName, intPrimTyCon, intPrimTy, intPrimTyConName, @@ -80,6 +80,8 @@ module TysPrim( #include "HsVersions.h" +import GhcPrelude + import {-# SOURCE #-} TysWiredIn ( runtimeRepTy, unboxedTupleKind, liftedTypeKind , vecRepDataConTyCon, tupleRepDataConTyCon @@ -94,7 +96,7 @@ import {-# SOURCE #-} TysWiredIn , doubleElemRepDataConTy , mkPromotedListTy ) -import Var ( TyVar, TyVarBndr(TvBndr), mkTyVar ) +import Var ( TyVar, VarBndr(Bndr), mkTyVar ) import Name import TyCon import SrcLoc @@ -116,7 +118,22 @@ import Data.Char -} primTyCons :: [TyCon] -primTyCons +primTyCons = unexposedPrimTyCons ++ exposedPrimTyCons + +-- | Primitive 'TyCon's that are defined in "GHC.Prim" but not exposed. +-- It's important to keep these separate as we don't want users to be able to +-- write them (see Trac #15209) or see them in GHCi's @:browse@ output +-- (see Trac #12023). +unexposedPrimTyCons :: [TyCon] +unexposedPrimTyCons + = [ eqPrimTyCon + , eqReprPrimTyCon + , eqPhantPrimTyCon + ] + +-- | Primitive 'TyCon's that are defined in, and exported from, "GHC.Prim". +exposedPrimTyCons :: [TyCon] +exposedPrimTyCons = [ addrPrimTyCon , arrayPrimTyCon , byteArrayPrimTyCon @@ -148,9 +165,6 @@ primTyCons , wordPrimTyCon , word32PrimTyCon , word64PrimTyCon - , eqPrimTyCon - , eqReprPrimTyCon - , eqPhantPrimTyCon , tYPETyCon @@ -326,7 +340,7 @@ openBetaTy = mkTyVarTy openBetaTyVar -} funTyConName :: Name -funTyConName = mkPrimTyConName (fsLit "(->)") funTyConKey funTyCon +funTyConName = mkPrimTyConName (fsLit "->") funTyConKey funTyCon -- | The @(->)@ type constructor. -- @@ -337,8 +351,8 @@ funTyConName = mkPrimTyConName (fsLit "(->)") funTyConKey funTyCon funTyCon :: TyCon funTyCon = mkFunTyCon funTyConName tc_bndrs tc_rep_nm where - tc_bndrs = [ TvBndr runtimeRep1TyVar (NamedTCB Inferred) - , TvBndr runtimeRep2TyVar (NamedTCB Inferred) + tc_bndrs = [ Bndr runtimeRep1TyVar (NamedTCB Inferred) + , Bndr runtimeRep2TyVar (NamedTCB Inferred) ] ++ mkTemplateAnonTyConBinders [ tYPE runtimeRep1Ty , tYPE runtimeRep2Ty @@ -580,18 +594,19 @@ Note [The equality types story] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ GHC sports a veritable menagerie of equality types: - Hetero? Levity Result Role Defining module - ------------------------------------------------------------ - ~# hetero unlifted # nominal GHC.Prim - ~~ hetero lifted Constraint nominal GHC.Types - ~ homo lifted Constraint nominal Data.Type.Equality - :~: homo lifted * nominal Data.Type.Equality - - ~R# hetero unlifted # repr GHC.Prim - Coercible homo lifted Constraint repr GHC.Types - Coercion homo lifted * repr Data.Type.Coercion + Type or Lifted? Hetero? Role Built in Defining module + class? L/U TyCon +----------------------------------------------------------------------------------------- +~# T U hetero nominal eqPrimTyCon GHC.Prim +~~ C L hetero nominal heqTyCon GHC.Types +~ C L homo nominal eqTyCon GHC.Types +:~: T L homo nominal (not built-in) Data.Type.Equality +:~~: T L hetero nominal (not built-in) Data.Type.Equality - ~P# hetero unlifted phantom GHC.Prim +~R# T U hetero repr eqReprPrimTy GHC.Prim +Coercible C L homo repr coercibleTyCon GHC.Types +Coercion T L homo repr (not built-in) Data.Type.Coercion +~P# T U hetero phantom eqPhantPrimTyCon GHC.Prim Recall that "hetero" means the equality can related types of different kinds. Knowing that (t1 ~# t2) or (t1 ~R# t2) or even that (t1 ~P# t2) @@ -627,6 +642,7 @@ This is (almost) an ordinary class, defined as if by class a ~# b => a ~~ b instance a ~# b => a ~~ b Here's what's unusual about it: + * We can't actually declare it that way because we don't have syntax for ~#. And ~# isn't a constraint, so even if we could write it, it wouldn't kind check. @@ -636,8 +652,8 @@ Here's what's unusual about it: * It is "naturally coherent". This means that the solver won't hesitate to solve a goal of type (a ~~ b) even if there is, say (Int ~~ c) in the context. (Normally, it waits to learn more, just in case the given - influences what happens next.) This is quite like having - IncoherentInstances enabled. + influences what happens next.) See Note [Naturally coherent classes] + in TcInteract. * It always terminates. That is, in the UndecidableInstances checks, we don't worry if a (~~) constraint is too big, as we know that solving @@ -656,28 +672,31 @@ Within GHC, ~~ is called heqTyCon, and it is defined in TysWiredIn. -------------------------- (~) :: forall k. k -> k -> Constraint -------------------------- -This is defined in Data.Type.Equality: - class a ~~ b => (a :: k) ~ (b :: k) - instance a ~~ b => a ~ b -This is even more so an ordinary class than (~~), with the following exceptions: - * Users cannot write instances of it. +This is /exactly/ like (~~), except with a homogeneous kind. +It is an almost-ordinary class defined as if by + class a ~# b => (a :: k) ~ (b :: k) + instance a ~# b => a ~ b - * It is "naturally coherent". (See (~~).) + * All the bullets for (~~) apply - * (~) is magical syntax, as ~ is a reserved symbol. It cannot be exported - or imported. + * In addition (~) is magical syntax, as ~ is a reserved symbol. + It cannot be exported or imported. - * It always terminates. +Within GHC, ~ is called eqTyCon, and it is defined in TysWiredIn. -Within GHC, ~ is called eqTyCon, and it is defined in PrelNames. Note that -it is *not* wired in. +Historical note: prior to July 18 (~) was defined as a + more-ordinary class with (~~) as a superclass. But that made it + special in different ways; and the extra superclass selections to + get from (~) to (~#) via (~~) were tiresome. Now it's defined + uniformly with (~~) and Coercible; much nicer.) -------------------------- (:~:) :: forall k. k -> k -> * + (:~~:) :: forall k1 k2. k1 -> k2 -> * -------------------------- -This is a perfectly ordinary GADT, wrapping (~). It is not defined within -GHC at all. +These are perfectly ordinary GADTs, wrapping (~) and (~~) resp. +They are not defined within GHC at all. -------------------------- |