gistfile1.lisp

; http://tapestryjava.blogspot.se/2013/02/crafting-code-in-clojure.html
;
; Extract all the keys from both maps
; Remove any duplicates
; Convert the keys to strings
; Sort the strings into ascending order
; Build and return one big string, by concatenating all the key strings, using ", " as a separator
; Return "<none>" if both maps are empty

(defun hash-table-keys (hash-table)
  (loop for key being the hash-key of hash-table collect key))

(defun example (&rest hash-tables)
  (format nil "~:[<none>~;~:*~{~A~^, ~}~]"
          (sort (remove-duplicates (mapcan 'hash-table-keys hash-tables) :test #'equal)
                'string<)))