Implement a package for some game mechanics

Currently can deal some hands and redeal some cards.

src/game.lisp

@@ -0,0 +1,47 @@
+;;; game.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:
+
+;; Game mechanic code.
+
+;;; Code:
+
+(in-package :cantedraw.game)
+
+(fn deal-cards (n deck) (-> (fixnum cardset) (cons cardset cardset))
+  (destructuring-bind (hand . rest) (split n deck)
+    (cons (sort hand #'card<) rest)))
+
+(fn deal-hands (n deck) (-> (fixnum cardset) (cons list cardset))
+  (if (< (length deck) (* 5 n))
+      (error "Require at least ~a cards for ~a hands, but have ~a cards!"
+             n (* 5 n) (length deck)))
+  (loop :for i :from 1 :to n
+        :for (hand . rest) = (deal-cards 5 deck) :then (deal-cards 5 rest)
+        :collect hand :into x
+        :finally (return (cons x rest))))
+
+(fn redeal-hand (hand indices deck) (-> (cardset list cardset)
+                                        (cons cardset cardset))
+  (cond
+    ((null indices) (cons hand deck))
+    ((= 5 (length indices)) (deal-cards 5 deck))
+    (t
+     (destructuring-bind (new-cards . deck)
+         (deal-cards (length indices) deck)
+       (--> it
+         (remove-at-indices indices hand)
+         (append it new-cards)
+         (sort it #'card<)
+         (cons it deck))))))