#8714: ExistentialQuantification plus DeriveDataTypeable leads to core lint error -------------------------------------+---------------------------------- Reporter: CoreyOConnor | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.6.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: x86_64 (amd64) Type of failure: None/Unknown | Difficulty: Unknown Test Case: | Blocked By: Blocking: | Related Tickets: -------------------------------------+---------------------------------- Comment (by simonpj): Well nailed! We need the cloning because when we float bindings out we might widen the scope of its binders, and we don't want to accidentally capture an un- related occurrence. Originally we only floated let-bindings, which bind only Ids, and so the substitution substituted only for Ids. But now we flaot case-expressions too, and they can bind type variables. Once the substitution binds type variables it must be applied to many more things (e.g. the types of other binders) which is not done at all at the moment. So your diagnosis is right but the fix isn't a one-liner. I'll work on it. Simon -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8714#comment:6 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler