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| author | Simon Peyton Jones <simonpj@microsoft.com> | 2017-11-08 08:23:53 +0000 |
|---|---|---|
| committer | Simon Peyton Jones <simonpj@microsoft.com> | 2017-11-08 11:12:33 +0000 |
| commit | 21970de8bf810970a9f4d634d53ea02b2cb248db (patch) | |
| tree | 4b60aad3e3f0e11797f2a6f9ef2890de09e0a5aa /compiler/prelude | |
| parent | 14d885e843f6907dbc5048ae66aca25d738e99f7 (diff) | |
| download | haskell-21970de8bf810970a9f4d634d53ea02b2cb248db.tar.gz | |
Imrpove comments about equality types
Diffstat (limited to 'compiler/prelude')
| -rw-r--r-- | compiler/prelude/TysPrim.hs | 25 | ||||
| -rw-r--r-- | compiler/prelude/TysWiredIn.hs | 2 |
2 files changed, 15 insertions, 12 deletions
diff --git a/compiler/prelude/TysPrim.hs b/compiler/prelude/TysPrim.hs index 5c099e845e..f7a51a535e 100644 --- a/compiler/prelude/TysPrim.hs +++ b/compiler/prelude/TysPrim.hs @@ -582,17 +582,19 @@ Note [The equality types story] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ GHC sports a veritable menagerie of equality types: - Built-in tc Hetero? Levity Result Role Defining module + Type or Lifted? Hetero? Role Built in Defining module + class? L/U TyCon ----------------------------------------------------------------------------------------- -~# eqPrimTyCon hetero unlifted # nominal GHC.Prim -~~ hEqTyCon hetero lifted Constraint nominal GHC.Types -~ eqTyCon homo lifted Constraint nominal Data.Type.Equality -:~: - homo lifted * nominal Data.Type.Equality +~# T U hetero nominal eqPrimTyCon GHC.Prim +~~ C L hetero nominal hEqTyCon GHC.Types +~ C L homo nominal eqTyCon Data.Type.Equality +:~: T L homo nominal (not built-in) Data.Type.Equality +:~~: T L hetero nominal (not built-in) Data.Type.Equality -~R# eqReprPrimTy hetero unlifted # repr GHC.Prim -Coercible coercibleTyCon homo lifted Constraint repr GHC.Types -Coercion - homo lifted * repr Data.Type.Coercion -~P# eqPhantPrimTyCon 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) @@ -676,9 +678,10 @@ it is *not* wired in. -------------------------- (:~:) :: 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. -------------------------- diff --git a/compiler/prelude/TysWiredIn.hs b/compiler/prelude/TysWiredIn.hs index 2033fcff36..32c6117041 100644 --- a/compiler/prelude/TysWiredIn.hs +++ b/compiler/prelude/TysWiredIn.hs @@ -1009,7 +1009,7 @@ mk_sum arity = (tycon, sum_cons) ********************************************************************* -} -- See Note [The equality types story] in TysPrim --- (:~~: :: forall k1 k2 (a :: k1) (b :: k2). a -> b -> Constraint) +-- ((~~) :: forall k1 k2 (a :: k1) (b :: k2). a -> b -> Constraint) -- -- It's tempting to put functional dependencies on (~~), but it's not -- necessary because the functional-dependency coverage check looks |