#14584: Core Lint error -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 Resolution: | Keywords: TypeInType, | DeferredTypeErrors 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): * cc: goldfire (added) Comment: Yurgh. I don't yet understand the details, but what is happening is something like this. We have an implication constraint {{{ forall x[2]. [W] co1: alpaha[1] ~ ty |> co2 [W] co2: k1 ~ * }}} Here `co2` is an ultimately-unsolved kind coercion. We float `co1` out of the implication and unify with `alpha`. Then in `TcErrors` we make evidence for `co2` using a call to `error`, bound in the `EvBinds` for the implication. But alas the scope of the binding for `co2` is just the term enclosed by the implication constraint. But the use of `co2` has escaped, in the type `alpha`. Yikes. This only shows up with deferred type errors, because normally we don't make term-level bindings for coercions; instead we just side-effect them right into the coercions they are used in, which just happens to work even in the "escaping" case. But with deferred type errors we need to force a term-level error, and to do so in as narrow a scope as possible. I'd like a smaller test case to show this up. I really do not know how to solve this. It's all because of those pesky casts inside types! Richard, your advice would be valuable here. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14584#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler