Certainly you can implement the typechecker with macros, but it should also work on macros, before expansion. That is, you likely want (-> ...) typechecked as written, not (only) as expanded, and typing errors reported on the non-expanded form.
Word. This is a problem of lisps in general, they loose information as the same "thing" traverse the various meta-layers that constitute the system. A parsed expression is not tied to its string, and the expansion of the expression, provided it is a macro, is not tied to the original expression. In the same vein: you can't easily find the source code of a lambda that was compiled/interpreted.
Of course you can do all of this, but you need to build it yourself: see rewrite-clj. If you want to build a clojure debugger that is able to display or refer to code with the same indentation the programmer is dealing with in his text editor, you need to bridge the gap between clojure expressiosn and their string representation.
Anyway I concur that reversible macros would be great. Tag the output, have those tags propagate to the input by playing the macro backwards. Complex stuff really. That's a job for category theory I guess.
