Yes, Typed Racket does have that -- DrRacket continuously expands in the background, so Typed Racket gets it for free by integrating into the macro system. The

Yes, Typed Racket does have that -- DrRacket continuously expands in the background, so Typed Racket gets it for free by integrating into the macro system. The Typed Racket type checker is much slower than Hack, though. Hack does seem to have polymorphic data structures and higher-order functions.