Two Years of GNU Guile Scheme 2.0
Two years ago Guile Scheme, the official extension language of the GNU project, released version 2.0, a major upgrade to the implementation. As part of the two year anniversary, the maintainers organized a challenge to hack a small project using Guile in 30 days as part of a birthday software potluck. The two coolest dishes appear to be OpenGL support using the FFI, and XCB bindings built using the XML specification for XCB: "guile-xcb is a language implemented in the Guile VM that parses the XML
files used by the xcb project to specify the X protocol and compiles
them into Guile modules containing all the methods and data needed to
send requests to the X server and receive replies/events back. If new X
extensions are added to the xcb library, guile-xcb can compile and add
them with no additional work.
"
See the release announcement for details on the other dishes.
Plenty of LISPs break that "rule", and usually for the better. Clojure wouldn't be the tremendously practical and useful language it is if it didn't have vectors, maps, queues, and the like.
What's important is that the language retains isomorphism (and thus, LISP's full measure of metaprogramming power) -- as long as your parse tree and your code map 1:1, adding some additional types does no harm and a world of good.