I can see that, but it doesn't feel quite right. The tree you get directly from deserialized source text is still a bit more fine grained than I'd expect a true AST to be.

To see what I mean, consider this:

    (if condition 1 2 3)

This expression can be deserialized into a Lisp data structure, but it still contains a syntax error, and I don't think a true AST would be able to represent that syntax error.