Could you possibly give us an update about the current status of your pattern checker work? I know the number of tickets may seem a bit overwhelming; please reach out to the ghc-devs list, or individual developers, to get whatever help you need. Knocking out some of these tickets is a priority for 8.2, and the freeze is coming up fast. In my mind, the top priorities for GHC 8.2 should probably be #10746 and #12949. We really want to get those squashed. I think #11195 is also a fairly high priority (if it's still an issue!). #10746 is a serious correctness issue, and Simon's suggested fix sounds straightforward. Have you run into trouble? #12949 is also a serious correctness issue. You're right that desugaring doesn't happen till after type checking, but I believe the type checker should have already worked out what it needs to be able to desugar the overloading. It would be worth asking how you might access that information. #11195 looks like a practically important and serious performance problem. I know you spent some time investigating it months ago; do you have any more recent progress to report? Do you know if the problem is still there? David Feuer