This is such a cool idea.
One potential application is doing something like F#'s type providers for typed access to a SQL database.
You could use `trivial` to get fully typed SELECT statements integrated with Typed Racket.
In fact, Ben has already done some thinking along these lines: section 3.6 of http://www.ccs.neu.edu/home/types/cv/failures/icfp-2016-reje... sketches out the idea, and there is some stubbed-out code in the `trivial` git repo waiting to be dusted off.
