csv.lisp

(defun map-csv-file (fun file)
  (let ((buffer (make-string 512)))
    (with-open-file (stream file)
      (let (fields
            (read 0)
            (start 0)
            concat
            escaping)
        (loop
          do
          (setf read (read-sequence buffer stream)
                start 0)
          (loop for n below read
                for char = (aref buffer n)
                do (flet ((end-field ()
                            (let ((field (subseq buffer start n)))
                              (when concat
                                (push field concat)
                                (setf field (apply #'concatenate 'string (nreverse concat))
                                      concat nil))
                              (push field fields))))
                     (if escaping
                         (case char
                           (#\"
                            (end-field)
                            (setf escaping nil)
                            (setf start (1+ n))))
                         (case char
                           (#\Return
                            (when (or concat
                                      (> n start))
                              (end-field))
                            (funcall fun (nreverse fields))
                            (setf fields nil)
                            (setf start (1+ n)))
                           (#\Newline
                            (setf start (1+ n)))
                           (#\,
                            (end-field)
                            (setf start (1+ n)))
                           (#\"
                            (setf escaping t)
                            (setf start (1+ n)))))))
          (when (> read start)
            (push (subseq buffer start read)
                  concat))
          while (= read (length buffer)))))))