Prototype of dimensional numbers implementation

unit-numbers.lisp

(set-dispatch-macro-character #\# #\M #'read-dimensional-number)
(set-dispatch-macro-character #\# #\I #'read-dimensional-number)

(defun read-dimensional-number (s c n)
  (declare (ignore n))
  (let* ((prev-case (readtable-case *readtable*))
         (val (unwind-protect
                  (progn (setf (readtable-case *readtable*) :preserve)
                         (symbol-name (read s nil)))
                (setf (readtable-case *readtable*) prev-case)))
         (split-pos (position-if-not (lambda (ch)
                                       (or (digit-char-p ch)
                                           (member ch '(#\- #\.))))
                                     val)))
    (convert-to-SI c
                   (read-from-string (subseq val 0 split-pos))
                   (intern (subseq val split-pos) :keyword))))

(defgeneric convert-to-SI (system number unit))

(defmethod convert-to-SI ((system (eql #\M)) number (unit (eql :m/s2)))
  number)

(defmethod convert-to-SI ((system (eql #\M)) number (unit (eql :kJ)))
  (* 1000 number))

(defmethod convert-to-SI ((system (eql #\M)) number (unit (eql :cal)))
  (* 4.184 number))

(defmethod convert-to-SI ((system (eql #\I)) number (unit (eql :lb)))
  (* 453.592 number))