[hyperion2010]

Fantastic. Apparently I am not the only one that has been digging around for more detailed information about how CL implements static typing. There is so much FUD out there from the ??? community(ies) that I ended up sitting down and finding the relevant sections in my lab's copy of CLTL2. This article does an excellent job of laying out the consequences of the standard in a way that is clear and understandable, and probably that also includes knowledge about those consequences that was not entirely known at the time (or maybe it was, but just not documented).

I kind of wish the author had named his type defun `defunct` though!

[dreamcompiler]

As reikonomusha points out, this article is highly SBCL-specific. Other Common Lisps typically use type declarations more as reasons not to check types at runtime. SBCL on the other hand also uses type declarations to reason about types at compile time.