(defvar *checks* (make-array 100 :adjustable t :fill-pointer 0)
  "A vector of checks.")

(defconstant +first-check-number+ 100
   "The number of the first check.")

(defvar *next-check-number* +first-check-number+
  "The number of the next check.")

(defvar *payees* (make-hash-table :test #'equal)
  "Payees with checks paid to each.")

(defstruct check
  number date amount payee memo)

(defun current-date-string ()
  "Returns current date as a string."
  (multiple-value-bind (sec min hr day mon yr)
	  (get-decoded-time)
	(declare (ignore sec min hr))
	(format nil "~A-~A-~A" yr mon day)))

(defun write-check (amount payee memo)
  "Writes the next check in sequence."
  (let ((new-check (make-check
					:number *next-check-number*
					:date (current-date-string)
					:amount amount
					:payee payee
					:memo memo)))
	(incf *next-check-number*)
	(vector-push-extend new-check *checks*)
	(push new-check (gethash payee *payees*))
	new-check))

(defun get-check (number)
  "Returns a check given its number, or NIL if no such check."
  (when (and (<= +first-check-number+ number) (< number *next-check-number*))
	(aref *checks* (- number +first-check-number+))))

(defun void-check (number)
  "Voids a check and returns T.  Returns NIL if no such check."
  (let ((check (get-check number)))
	(when check
	  (setf (gethash (check-payee check) *payees*)
			(delete check (gethash (check-payee check) *payees*)))
	  (setf (aref *checks* (- number +first-check-number+)) nil)
	  t)))

(defun list-checks (payee)
  "Lists all of the checks written to payee."
  (gethash payee *payees*))

(defun list-all-checks ()
  "Lists all checks written."
  (coerce *checks* 'list))

(defun sum-checks ()
  (let ((sum 0))
	(map nil #'(lambda (check)
				 (when check
				   (incf sum (check-amount check))))
		 *checks*)
	sum))

(defun list-payees ()
  "Lists all payees."
  (let ((payees ()))
	(maphash #'(lambda (key value)
				 (declare (ignore value))
				 (push key payees))
			 *payees*)
	    payees))