Start server

server/game.lisp

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+(in-package :remote-snake-server-game)
+
+(defclass game ()
+  ((initial-size
+    :initarg :initial-size
+    :initform 3)
+   (initial-position
+    :initarg :initial-position
+    :initform (list 0 0))
+   (snake
+    :accessor snake)
+   (dir
+    :initarg :initial-direction
+    :initform :right)))
+
+;;; Class constructor to initialize the snake
+(defmethod initialize-instance :after ((g game) &key)
+  (with-slots (snake initial-size initial-position) g
+  (setf snake (make-array initial-size :initial-element initial-position))))
+
+;;; Pretty-print a game
+(defmethod print-object ((g game) stream)
+  (with-slots (snake dir) g
+    (format t "Snake:      ")
+    (dotimes (i (first (array-dimensions snake)))
+      (let ((elem (aref snake i)))
+        (unless (eql i 0)
+          (format t "<="))
+        (format t "(~a,~a)" (first elem) (second elem))))
+    (format t "~%Size:       ~a" (first (array-dimensions snake)))
+    (format t "~%Direction:  ~a" dir)))
+
+(defgeneric refresh (g &key)
+  (:documentation "Refresh the game g (move forward or change direction)."))
+
+;;; Return true when doing a legal move (ex: snake can goto left when it is in the right direction)
+(defun legal-move (active-dir dir)
+  (or
+   (eq active-dir dir) ; Goto same direction
+   (and (or (eq dir :up) (eq dir :down)) ; Got up or down only if the snake is on the left or right direction
+        (or (eq active-dir :left) (eq active-dir :right)))
+   (and (or (eq dir :left) (eq dir :right)) ; Goto left or right only if the snake is on the up or down direction
+        (or (eq active-dir :up) (eq active-dir :down)))))
+
+(defmethod refresh ((g game) &key (dir nil dir-supplied-p))
+  ;; First, update direction
+  (with-slots ((active-dir dir)) g
+      (when dir-supplied-p
+        (if (and
+             (or (eq dir :up) (eq dir :down) (eq dir :left) (eq dir :right))
+             (legal-move active-dir dir))
+                 (setf (slot-value g 'dir) dir)
+                 (error "Invalid direction supplied"))))
+  ;; Then, move the snake
+  (with-slots (snake dir) g
+    (let ((last-old-x nil) (last-old-y nil))
+      (dotimes (i (first (array-dimensions snake)))
+        (let ((elem (aref snake i)))
+          (let ((x (first elem)) (y (second elem)))
+            ;; Move snake
+            (if (eql i 0) ; Move head
+                (progn
+                  ;; Update last-old-x and last-old-y (to move the body when i>0)
+                  (setf last-old-x x)
+                  (setf last-old-y y)
+                  (cond ((eq dir :up) (incf y))
+                        ((eq dir :down) (decf y))
+                        ((eq dir :left) (decf x))
+                        ((eq dir :right) (incf x))))
+              (progn ; Move body
+                  (rotatef x last-old-x)
+                  (rotatef y last-old-y)))
+            (format t "l:(~a,~a) n:(~a,~a) ~%" last-old-x last-old-y x y)
+            (setf (aref snake i) (list x y))))))) ; Apply new snake location (update snake slot)
+              
+  ;; Check if we loose
+  )

server/packages.lisp

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+(defpackage :remote-snake-server-game
+  (:nicknames :rssg)
+  (:use :common-lisp)
+  (:export
+   #:game))

server/remote-snake-server.asd

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+
+(defsystem "remote-snake-server"
+  :description "Remote Snake Server."
+  :version "0.0.1"
+  :author "Loic Guegan"
+  :depends-on ( "usocket" "jonathan")
+  :components ((:file "packages")
+               (:file "game")))