Add a package for modelling cards

Time to do the fun non-yakshaving part.  I'll start out by writing
some custom types for the objects of concern: ranks, suits, cards and
sets of cards.

model.lisp

@@ -0,0 +1,37 @@
+;;; model.lisp - 2025-02-14
+
+;; Copyright (C) 2025 Aryadev Chavali
+
+;; This program is distributed in the hope that it will be useful, but WITHOUT
+;; ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+;; FOR A PARTICULAR PURPOSE.  See the GNU General Public License Version 2 for
+;; details.
+
+;; You may distribute and modify this code under the terms of the GNU General
+;; Public License Version 2, which you should have received a copy of along with
+;; this program.  If not, please go to <https://www.gnu.org/licenses/>.
+
+;;; Commentary:
+
+;; Model of cards and sets of cards in Lisp.
+
+;;; Code:
+
+(in-package :cantedraw.model)
+
+(deftype rank ()
+  `(or (member :Jack :Queen :King :Ace)
+       (integer 2 10)))
+
+(deftype suit ()
+  `(member :Diamonds :Clubs :Hearts :Spades :Joker))
+
+(deftype card () `(cons rank suit))
+
+(deftype int-card () `(integer 0 51))
+
+(fn cardsetp (lst) (-> (list) boolean)
+  (every #'(lambda (x) (typep x 'card)) lst))
+
+(deftype cardset () `(and list (satisfies cardsetp)))
+