Player handler package

This package defines a player data structure, collections of players,
and different interactions you can have with them:
- Extracting attributes (destructors)
- Checking if they're bankrupt or can bet
- Modifying a collection to adjust the balance of any one
  player (including errors in case that isn't possible)

src/player.lisp

@@ -0,0 +1,72 @@
+;;; player.lisp - 2025-02-15
+
+;; 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:
+
+;; Player management - in particular, financing and hand management.
+
+;;; Code:
+
+(in-package :cantedraw.player)
+
+(defun playerp (x)
+  (and (typep (car x) 'fixnum)
+       (typep (cadr x) 'fixnum)
+       (typep (caddr x) 'cardset)))
+
+(deftype player () `(and cons (satisfies playerp)))
+
+(deftype players () 'list)
+
+(fn player-id (player) (-> (player) fixnum)
+  (car player))
+
+(fn player-balance (player) (-> (player) fixnum)
+  (cadr player))
+
+(fn player-hand (player) (-> (player) cardset)
+  (caddr player))
+
+(fn player-exists? (id players) (-> (fixnum players) boolean)
+  (assoc id players))
+
+(fn player-bankrupt? (player) (-> (player) boolean)
+  (<= (cadr player) 0))
+
+(fn player-can-bet? (min-bet player) (-> (fixnum player) boolean)
+  (>= (cadr player) min-bet))
+
+(fn player-pay (id amount players) (-> (fixnum fixnum players) players)
+  (let ((p (assoc id players)))
+    (cond
+      ((not (typep p 'player))
+       (error "Player [~a] does not exist."))
+      ((not (player-can-bet? amount p))
+       (error "Player [~a] has $~a but needs to pay ~a."
+              id (player-balance p) amount))
+      (t
+       (destructuring-bind (id balance cards) p
+         (setf (cdr (assoc id players))
+               (list (- balance amount) cards)))))
+    players))
+
+(fn player-receive (id amount players)
+    (-> (fixnum fixnum players) players)
+  (let ((p (assoc id players)))
+    (if (not (typep p 'player))
+        (error 'error-player-nonexistent
+               :id id))
+    (destructuring-bind (id balance cards) p
+      (setf (cdr (assoc id players))
+            (list (+ balance amount) cards)))
+    players))