I'd have to disagree, considering that GHC maintains similar speeds to Mono and JVM languages. The question was about functional languages being slower, but he didn't specify slower than what. If the unspecified alternative is imperative languages, then there are plenty of imperative languages that are slower in that graph and will likely never be as fast as Haskell. Granted, functional languages are never going to be as fast as low-level languages like C, but that doesn't mean they're necessarily slow either.