Hi all, I wanted to bring to your attention this bug, https://ghc.haskell.org/trac/ghc/ticket/10218 , which I filed about two days ago but hasn't gotten any replies to yet. In my opinion, this is a rather serious bug since GHC is producing incorrect code. While there is a workaround, it makes my program take about 2 hours to compile. Since reporting the bug, I've also seen "strange closure type" exceptions, which I believe are also caused by this bug, although I do not have a test case. Based on my limited understanding of GHC internals, I suspect the problem lies in how type class dictionaries are looked up at run time, as the problem disappears if GHC can fully resolve the types. Can others see if they can reproduce this bug? If there is any way I can help, please let me know. Sincerely, Yongqian Li