#13750: GHC produces incorrect coercions in hairy code -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: (none) Type: bug | Status: new Priority: highest | Milestone: 8.2.2 Component: Compiler | Version: 8.2.1-rc2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: Runtime crash | Test Case: Blocked By: | Blocking: Related Tickets: #13429 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by RyanGlScott): I'm no "type guru", but I find this development quite unsurprising. The "utterly bogus definition" that you pointed out in the original comment concerns the `All` type class, which has `AllF` as a superclass. The nub of #13429 concerns improper specialization of dictionary functions with superclasses, and `All` falls into the category. Combine incorrect specialization with `unsafeCoerce`, and segfaults are just around the corner. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13750#comment:11 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler