Use green-threads to build a "blocking" interface for an asynchronous library.

async.lisp

;; you'll need to clone green-threads and cl-async into ~/quicklisp/local-projects
(ql:quickload "green-threads")
(ql:quickload "cl-async")

(defun f-http-client (url &rest rest)
  (let ((http-future (green-threads:make-future)))
    (apply #'cl-async:http-client
           url
           #'(lambda (status headers body)
               (green-threads:complete-future 
                 http-future status headers body nil))
           #'(lambda (err)
               (green-threads:complete-future
                 http-future nil nil nil err))
           rest)
    http-future))

(cl-async:start-event-loop
  (lambda ()
    (green-threads:with-green-thread
      (let ((f1 (f-http-client "http://blog.thezerobit.com/" :timeout 5))
            (f2 (f-http-client "http://blog.deliciousrobots.com/" :timeout 5)))
        (multiple-value-bind
          (status headers body err) (green-threads:wait-on f1)
          (when (not err)
            (format t "Status: ~a bytes: ~a Headers: ~a~%" 
                    status (length body) (length headers))))
        (multiple-value-bind
          (status headers body err) (green-threads:wait-on f2)
          (when (not err)
            (format t "Status: ~a bytes: ~a Headers: ~a~%" 
                    status (length body) (length headers))))))))