#12957: In a record-update construct:ghc-stage2: panic! (the 'impossible' happened) -------------------------------------+------------------------------------- Reporter: niteria | Owner: mpickering Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 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:D3065, Wiki Page: | Phab:D3064 -------------------------------------+------------------------------------- Changes (by mpickering): * differential: => Phab:D3065, Phab:D3064 Comment: There was actually a bug in the PM checker which was causing this bug to show up. Here is a simpler reproduction. Essentially the checker was seeing that `[]` was not consistent with `(_:_)` and thus for any nested pattern matches the initial uncovered set was empty which caused all patterns to be reported as redundant. {{{ module T12957 where data A = N | A { b :: Bool } f = case [] of (_:_) -> case () of a -> undefined }}} However, it was also good to add the case to `matchSeparator` as these matches are printed when `-ddump-ec-trace` is used. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12957#comment:7 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler