Just to make it clear, the authors of that paper (including myself) are all to some extent Racket developers. Some big improvements have been made but there are

Just to make it clear, the authors of that paper (including myself) are all to some extent Racket developers. Some big improvements have been made but there are still pathological cases. For the latest published on this see this paper: http://users.cs.northwestern.edu/~robby/pubs/papers/oopsla2018-fgsfs.pdf http://users.cs.northwestern.edu/~robby/pubs/papers/oopsla20... But also it's important to note that it's not Typed Racket or Racket in isolation that are slow, but the inter-mingling of the two due to contract overhead.