On the topic of the JVM frameworks, you have to understand that the JVM is a very finely tuned machine at this point, it has something like 10+ years of perform

On the topic of the JVM frameworks, you have to understand that the JVM is a very finely tuned machine at this point, it has something like 10+ years of performance tuning by a large portion of the entire industry behind it. Yesod just recently cracked the 1.0 release and has been going through massive changes in the last year or so, the fact that it performs as well as it does is a huge testament not only to Haskell as a language, but also to the work of Michael Snoyman and the others who's work he incorporated into Yesod. That said, there are still a lot of rough patches with Yesod, and I'm sure there are lots of opportunities to improve performance in various small ways. The main Haskell compiler (ghc) is constantly improving and many of the changes allow for smarter automatic optimizations to be applied by both the compiler and the runtime. With continued refinement I feel it's definitely possible for Yesod to match, and even exceed the performance of any of the JVM based languages, but as I said, there are a lot of performance optimizations baked into the JVM and it's probably going to take a while before Yesod (and WAI which it's built on) have similar levels of optimization in them.