#12881: GHC 8.0.2 regression involving OVERLAP annotations -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: Type: bug | Status: patch Priority: high | Milestone: 8.0.2 Component: Compiler | Version: 8.0.2-rc1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D2760 Wiki Page: | -------------------------------------+------------------------------------- Comment (by rwbarton): It is possible to write useful potentially-overlapping instances without marking them as overlapping, e.g. {{{#!hs {-# LANGUAGE FlexibleInstances #-} class C a where def :: a def = undefined instance C (Int, b) instance C (a, Char) }}} But happily GHC HEAD already accepts this case, somehow. (Maybe someone with 8.0.2-rc1 can confirm.) -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12881#comment:10 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler