The easiest way to install Clack is to take advantage of Quicklisp. Run the following code on your Lisp.
(ql:quickload :clack)
Then all libraries including dependencies will be downloaded and be installed automatically.
To verify that you have everything installed correctly, let's start a Clack server. You don't have to understand the following code now. It will be mentioned the next chapter.
(clack:clackup
(lambda (env)
(declare (ignore env))
'(200 (:content-type "text/plain") ("Hello, Clack!"))))
;-> Hunchentoot server is started.
Listening on localhost:5000.
# #x30200A102B3D>
Clack runs on localhost port 5000 by default. Open the URL http://127.0.0.1:5000/ on your browser and Clack show you "Hello, Clack!".
To stop the process, get back to REPL and execute the following code.
(clack:stop *)