[klibertp]

There are many cool features that Racket has out of the box, like very nice module system, delimited continuations, objects and classes and of course macros (both hygienic define-syntax-rule, syntax-case and unhygienic defmacro) and more.

But if I had to show one feature of Racked to make someone amazed, it wouldn't be any of those. It would be a simple program composed of a couple of files, and every file would start with different #lang. Like #lang racket, #lang lazy, #lang typed/racket, #lang datalog.

It's sufficiently mind-blowing that there are this many languages on top of Racket, but the real "killer app" is how seamlessly they integrate with each other.

The next thing I'd show would probably be Danny Yoo tutorial on how you can create even more languages like this: http://hashcollision.org/brainfudge/

[nextos]

It's almost like a practical Mozart/Oz with all Lisp awesomeness. CTM shows how programming with many different paradigms can be extremely powerful.