[p4] use -2map for mapping over 2d lists.

p4/p4.org

@@ -50,27 +50,39 @@ This is for part 1; easy
 : 1464
 
 Now for part two, we create a new data-char at each removal step
-I am not particularly happy style-wise, but that is it for today
+and count how many rolls have been removed
 #+begin_src emacs-lisp
-  (defun tensor (a b)
-    (-map (lambda (x) (--map (list it x) a)) b))
-
   (setq initial-roll-number (length (advent/coordinates-of ?@ data-char))
         current-roll-number (1+ initial-roll-number))
 
   (while (> current-roll-number
             (setq current-roll-number (length (advent/coordinates-of ?@ data-char))))
     (setq data-char
-        (-map (lambda (row)
-           (--map (if (and (= ?@ (advent/char-at it data-char))
-                           (<= 4 (rolls-adjacent it data-char)))
+          (--2map-indexed (if (and (= ?@ it)
+                                   (<= 4 (rolls-adjacent it-multi-index data-char)))
                               ?@ ?.)
-                  row))
-         (tensor (-iterate #'1+ 0 width)
-                 (-iterate #'1+ 0 height)))))
+                          data-char)))
 
   (- initial-roll-number current-roll-number)
 #+end_src
 
 #+RESULTS:
 : 8409
+
+#+begin_src emacs-lisp
+  (defun -2map (fun li)
+    (--map (-map fun it) li))
+
+  (defmacro --2map (form list)
+    `(-2map (lambda (it) ,form) ,list))
+
+  (defun -2map-indexed (fun li)
+    (-map-indexed (lambda (i row)
+                    (-map-indexed (lambda (j it)
+                                    (funcall fun i j it))
+                                  row))
+          li))
+
+  (defmacro --2map-indexed (form li)
+    `(-2map-indexed (lambda (it-index-1 it-index-2 it) ,form) ,li))
+#+end_src