Day 19

(defvar *letters* nil)
(defvar *steps* 0)
(defstruct coord nil (y 0) (x 0))
(defvar dir (new coord y 1 x 0))
(defvar p (new coord))
(defvar *map*
  (vec-list
   (mapcar (lambda (l)
             (vec-list
              (mapcar (lambda (c)
                        (caseq c
                               (#\space nil)
                               ((#\| #\- #\+) t)
                               (t c)))
                      l)))
           (get-lines))))
(defun is-in-bounds (y x)
    (and (<= 0 x (- (len [*map* 0]) 1))
     (<= 0 y (- (len *map*) 1))))

(defun find-new-dir ()
  (let ((new-dir (new coord))
        (new-p (copy-struct p))
        (slot (if (= dir.x 0) 'x 'y)))
    (inc (slot new-p slot))
    (if [[*map* new-p.y] new-p.x]
        (inc (slot new-dir slot)))
    (dec (slot new-p slot) 2)
    (if [[*map* new-p.y] new-p.x]
        (dec (slot new-dir slot)))
    (if (= new-dir.x new-dir.y) nil new-dir)))

(set p.x (car (where (fun use) [*map* 0])))
(while t
  (inc *steps*)
  (if (chrp [[*map* p.y] p.x])
      (set *letters* (cons [[*map* p.y] p.x] *letters*)))
  (cond ((or (not (is-in-bounds (+ p.y dir.y) (+ p.x dir.x)))
             (not [[*map* (+ p.y dir.y)] (+ p.x dir.x)]))
         (set dir (find-new-dir))
         (unless dir (return))))
  (inc p.x dir.x)
  (inc p.y dir.y))

(mapcar (fun put-char) (nreverse *letters*))
(format t "\n~a\n" *steps*)