Read a file containing lines like foo=bar and output to a new file like this (foo . bar)

read-write.lisp

(defun arabic_to_roman (filename)
  (cl-flet ((read-it ()
                  (with-open-file (in filename
                                      :direction :input
                                      :if-does-not-exist nil)
                                  (loop for line = (read-line in nil)
                                        for pos = (position \= line)
                                        while line collect (cons (subseq line 0 pos)
                                                                 (subseq line (1+ pos))))))
         (write-it (list)
                   (with-open-file (cl-stream #p"ar_out.txt"
                                           :direction :output
                                           :if-exists :overwrite
                                           :if-does-not-exist :create)
                                   (write list :stream stream :escape nil :readably nil :pretty nil))))
    (write-it (read-it))
    'done-read-write))