yeah the author does too much (and un-necessary stuff). To keep his stack just use the Caveman library has he does:

    (defparameter *web* (make-instance '<app>))

    @route GET "/"
    (defun index ()
      (render #P"index.tmpl"))

https://github.com/fukamachi/caveman/ (I like Mito and Djula, I'd go with Hunchentoot rather than Clack which is famously undocumented)