Hi, Prompted by this question: http://stackoverflow.com/questions/26538595/more-efficient-type-level-comput... I wrote some code today using closed type families and datakinds. Also, as a baseline, I typechecked the code using open type families from the original question. The two files are here: https://gist.github.com/gergoerdi/727f028e4c1ed158ac9a https://gist.github.com/gergoerdi/f96d1a9a58f5e3dccc18 On GHC 7.8.3, typechecking took about 45 seconds for each. However, on a 'perf' build of GHC 7.9 d8c437b3, with ghc-stage2, the first one took 1m3s and the second one 1m12s. A 40% and 60% increase in typechecking time, respectively! Is this some known regression, something surprising, or is 'perf' simply not the right build flavour for this kind of comparison? Bye, Gergo