Why would you do that in a doc-string? If you just `declare` the types with `declare` instead of putting them in the docstring, the compiler can also take advantage of them. Then the system can automatically tell you that information back. It will also infer the return type for you automatically.

A trivial example (your editor can do this for you):

    (defun add-string (a b)
      (declare (number a) (string b))
      "Parses b and adds to a"
      (+ a (parse-integer b)))

    CL-USER> (describe #'add-string)
    #<FUNCTION ADD-STRING>
      [compiled function]
    
    Lambda-list: (A B)
    Derived type: (FUNCTION (NUMBER STRING) (VALUES NUMBER &OPTIONAL))
    Documentation:
      Parses b and adds to a
    Source file: /home/bja/foo.lisp