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| author | Simon Peyton Jones <simonpj@microsoft.com> | 2017-09-26 15:02:09 +0100 |
|---|---|---|
| committer | Simon Peyton Jones <simonpj@microsoft.com> | 2017-09-26 15:06:16 +0100 |
| commit | c41ccbfa8aaeb99dd9a36cb3d99993f0fa039cdc (patch) | |
| tree | 7d41a806727d1ce407802f8a5c475333418c1151 /compiler/prelude/TysPrim.hs | |
| parent | 7446c7f68bd5addd2f2db0d8d5910fb963869c47 (diff) | |
| download | haskell-c41ccbfa8aaeb99dd9a36cb3d99993f0fa039cdc.tar.gz | |
Omit Typeable from the "naturally coherent" list
In doing something else (Trac #14218) I tripped over the
definition of "naturally coherent" classes. This patch
- Cocuments properly what that means
- Removes Typeable from the list, because now we know what
it meams, Typeable clearly doesn't belong.
No regressions.
(Actually the term "naturally coherent" seems a bit off.
More like "invertible" or something. But I left it.)
Diffstat (limited to 'compiler/prelude/TysPrim.hs')
| -rw-r--r-- | compiler/prelude/TysPrim.hs | 31 |
1 files changed, 15 insertions, 16 deletions
diff --git a/compiler/prelude/TysPrim.hs b/compiler/prelude/TysPrim.hs index b4a5b6b541..5c099e845e 100644 --- a/compiler/prelude/TysPrim.hs +++ b/compiler/prelude/TysPrim.hs @@ -582,18 +582,17 @@ 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 - - ~P# hetero unlifted phantom GHC.Prim + Built-in tc Hetero? Levity Result Role Defining module +----------------------------------------------------------------------------------------- +~# 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 + +~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 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) @@ -638,8 +637,8 @@ 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 @@ -666,8 +665,8 @@ This is even more so an ordinary class than (~~), with the following exceptions: * It is "naturally coherent". (See (~~).) - * (~) is magical syntax, as ~ is a reserved symbol. It cannot be exported - or imported. + * (~) is magical syntax, as ~ is a reserved symbol. + It cannot be exported or imported. * It always terminates. |