#13766: Confusing "redundant pattern match" in 8.0, no warning at all in 8.2 -------------------------------------+------------------------------------- Reporter: edsko | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: 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 mpickering): This is the expected behaviour, the commit message explains the reasoning. {{{ Previously when the checker encountered an unsatisfiable term of type context it would return an empty initial uncovered set. This caused all pattern matches in the context to be reported as redudant. This is arguably correct behaviour as they will never be reached but it is better to recover and provide accurate warnings for these cases to avoid error cascades. It would perhaps be better to report an error to the user about an inacessible branch but this is certainly better than many confusing redundant match warnings. }}} Warning that the RHS is inaccessible would be valuable but I don't think it's the domain of the pattern match checker to warn indirectly of this by warning of "redundant" clauses. So it looks like the tickets that Edward linked are more relevant. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13766#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler