[racket] typed racket, filters, and polymorphism

Robby Findler writes:

 > Whoops, sorry: this is the same thing Konrad was talking about! Duh.
 > Well, hopefully the link is useful.

It is, thanks! There's a lot of material explaining the background of
F#'s unit checker.

The problem is highly relevant in science and engineering, where
dimensional analysis is the equivalent of type checking in
programming, with the added benefit that no one questions its utility
or importance.

There is also some interesting material on the Haskell Wiki:

   http://www.haskell.org/haskellwiki/Physical_units

Unfortunately it is hard to see what exactly is going on there, since
every package on that list requires some arcane GHC extensions whose
precise impact on the type system is known only to Haskell insiders.

Konrad.