Hi Harendra,

I saw your comment on a ghc proposal 
(https://github.com/ghc-proposals/ghc-proposals/pull/343#issuecomment-650797297)
 that said you experienced perf regressions with -XTypeFamilies enabled (but no 
other changes). Are these reproducible in a way that can be shared publicly? 
And are the regressions in compile times or run times?

-XTypeFamilies enables -XMonoLocalBinds, which disables let-generalization on 
some nested lets. It is thus just barely conceivable that different Core is 
produced depending on this extension, and that there may be a possibility of 
performance changes. But this would be unexpected, and something worth 
investigating.

In other words: if you can, do please post a bug -- simply enabling 
-XTypeFamilies should not slow anything down!

Thanks,
Richard
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