(in-package #:json)

(defparameter number-parser
  (let ((signed-digits
          (comp ((sign (zero-or-one (unit (lambda (x) (or (char= x #\-)
                                                          (char= x #\+))))))
                 (natural (one-or-more (unit #'digit-char-p))))
            (cons sign natural))))
    (comp ((base (either signed-digits
                         (fail "Malformed number.")))
           (dot (zero-or-one (unit (lambda (x) (char= x #\.)))))
           (fraction (if dot
                       (either (one-or-more (unit #'digit-char-p))
                               (fail "Malformed fractional part."))
                       nothing))
           (e (zero-or-one (unit (lambda (x) (or (char= x #\e)
                                                 (char= x #\E))))))
           (exponent (if e
                       (either signed-digits
                               (fail "Malformed exponent part."))
                       nothing)))
      (list 'number base fraction exponent))))