no, adding type declarations to Lisp is the easy part. when it comes to static typing, standard Common Lisp offers very little.
Declaring types? That has been done. In Common Lisp:
(defun twice (n)
(declare (number n))
(the number (* n 2)))
* the type system and its capabilities
* make the operations of the type system sound
* determining sub-types
* type inference
* integration with the rest of the language (where data objects also have something like types)
Common Lisp provides lots of infrastructure for all kinds of things, but very little for a type system. For example in Lisp one can determine the value of an expression via EVAL, but there is no function to compute the type of an expression (other than a type of the computed value).
Static typing consists of (a) tagging variables with their type and (b) running a program that uses these type tags to check and/or rewrite the program.
It's easy to add type tags to a lisp program. It's just that Lisp doesn't specify that second program that checks and transforms the first. So I would say Lisp is half way there when it comes to static typing.
That's a pretty contrived argument though... :-)