#11142: Type-level skolem capture leads to core lint error -------------------------------------+------------------------------------- Reporter: goldfire | Owner: bgamari Type: bug | Status: new Priority: high | Milestone: 8.0.1 Component: Compiler (Type | Version: 7.10.2 checker) | Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by simonpj): * owner: => bgamari * priority: normal => high * milestone: => 8.0.1 Comment: Works fine with `wip/spj-wildcard-refactor`. Ben please add this as a regression test. We get {{{ $ ghc-stage1 -c T11142.hs -dcore-lint -fforce-recomp -ddump-types TYPE SIGNATURES foo :: forall (k :: BOX) (b :: k). (forall (a :: k). SameKind a b) -> () }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11142#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#11142: Type-level skolem capture leads to core lint error -------------------------------------+------------------------------------- Reporter: goldfire | Owner: bgamari Type: bug | Status: new Priority: high | Milestone: 8.0.1 Component: Compiler (Type | Version: 7.10.2 checker) | Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): Always top level; c.f. #4426. Needs documentation I agree Simon -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11142#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#11142: Type-level skolem capture leads to core lint error -------------------------------------+------------------------------------- Reporter: goldfire | Owner: bgamari Type: bug | Status: new Priority: high | Milestone: 8.0.1 Component: Compiler (Type | Version: 7.10.2 checker) | Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by goldfire): That's true -- but we're not talking about kind generalization here, because the user is asking for it (albeit a bit indirectly). So: all kind variables that GHC invents are always quantified at the top level, but previously, users could specify kind variables to be quantified below top level. If that ability has been removed, this is a real loss of expressiveness that will bite. However, it's all easily recovered with the capabilities of my branch, where you can write kind quantification directly. So perhaps it all works out. But there's a bad migration story, because there will be no way to write higher-rank kind quantification that works in both GHC 7.10 and GHC 8.0. In any case, we need to clearly document the new behavior in the release notes. Is it worth trying to resurrect the old behavior on your branch, just to ease migration? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11142#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#11142: Type-level skolem capture leads to core lint error -------------------------------------+------------------------------------- Reporter: goldfire | Owner: bgamari Type: bug | Status: new Priority: high | Milestone: 8.0.1 Component: Compiler (Type | Version: 7.10.2 checker) | Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by Richard Eisenberg ): In [changeset:"6746549772c5cc0ac66c0fce562f297f4d4b80a2/ghc" 67465497/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="6746549772c5cc0ac66c0fce562f297f4d4b80a2" Add kind equalities to GHC. This implements the ideas originally put forward in "System FC with Explicit Kind Equality" (ICFP'13). There are several noteworthy changes with this patch: * We now have casts in types. These change the kind of a type. See new constructor `CastTy`. * All types and all constructors can be promoted. This includes GADT constructors. GADT pattern matches take place in type family equations. In Core, types can now be applied to coercions via the `CoercionTy` constructor. * Coercions can now be heterogeneous, relating types of different kinds. A coercion proving `t1 :: k1 ~ t2 :: k2` proves both that `t1` and `t2` are the same and also that `k1` and `k2` are the same. * The `Coercion` type has been significantly enhanced. The documentation in `docs/core-spec/core-spec.pdf` reflects the new reality. * The type of `*` is now `*`. No more `BOX`. * Users can write explicit kind variables in their code, anywhere they can write type variables. For backward compatibility, automatic inference of kind-variable binding is still permitted. * The new extension `TypeInType` turns on the new user-facing features. * Type families and synonyms are now promoted to kinds. This causes trouble with parsing `*`, leading to the somewhat awkward new `HsAppsTy` constructor for `HsType`. This is dispatched with in the renamer, where the kind `*` can be told apart from a type-level multiplication operator. Without `-XTypeInType` the old behavior persists. With `-XTypeInType`, you need to import `Data.Kind` to get `*`, also known as `Type`. * The kind-checking algorithms in TcHsType have been significantly rewritten to allow for enhanced kinds. * The new features are still quite experimental and may be in flux. * TODO: Several open tickets: #11195, #11196, #11197, #11198, #11203. * TODO: Update user manual. Tickets addressed: #9017, #9173, #7961, #10524, #8566, #11142. Updates Haddock submodule. }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11142#comment:7 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler