emacs lisp exercise: latitude-longitude-decimalize

decimalize.el

;; http://xahlee.blogspot.com/2011/11/emacs-lisp-exercise-latitude-longitude.html

(defun latitude-longitude-decimalize (str)
  (destructuring-bind (lath latm lats latd lonh lonm lons lond)
      (split-string str "[^0-9.NEWS]+" t)
    (vector (latlon-helper latd lath latm lats)
            (latlon-helper lond lonh lonm lons))))

(defun latlon-helper (d &rest hms)
  (* (if (or (equal d "N") (equal d "E")) 1 -1)
     (reduce (lambda (a b) (+ b (/ a 60.0)))
             (mapcar 'string-to-number (reverse hms)))))

;; Example usage:

(latitude-longitude-decimalize "37°26′36.42″N 06°15′14.28″W")
[37.44345 -6.253966666666667]