#14561: Panic on levity polymorphic very unsafe coerce -------------------------------------+------------------------------------- Reporter: goldfire | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.3 Resolution: | Keywords: | LevityPolymorphism 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): I strongly prefer the latter. It makes me nervous not to have a true back- door to the type system (which we would lose if we dropped the levity- polymorphism from `unsafeCoerce#`). It should be easy enough to check for saturation in the desugarer. But, actually, there's a third option: * Allow silly uses of `unsafeCoerce#` to cause a panic. The user is clearly taking on the risk of a runtime crash with `unsafeCoerce#`. We could just say they also risk taking on a compile-time crash. In this case, I think the fix (the saturation check) is easy enough, but I don't feel strongly committed to eradicating a hard-to-fix panic if the user abuses the type system with such a low-level operation. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14561#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler