Day 17: Generalized solution with macros.

src/17-macro.rkt

@@ -0,0 +1,62 @@
+#lang curly-fn racket
+
+(require (for-syntax racket/syntax
+                     [only-in racket/list
+                              range
+                              make-list])
+         "../lib.rkt")
+
+(define input
+  (map string->list (problem-input 17)))
+
+(define (grid dim)
+  (for*/fold ([grid (hash)])
+             ([x (length (first input))]
+              [y (length input)])
+    (hash-set grid
+              `(,x ,y ,@(make-list (- dim 2) 0))
+              (list-ref (list-ref input y) x))))
+
+(define (actives chars)
+  (count #{char=? % #\#} chars))
+
+(define (in-range+ from to)
+  (in-range (- from 1) (+ to 2)))
+
+(define-syntax cycle
+  (λ (stx)
+    (syntax-case stx ()
+      [(_ dim grid)
+       (let ([dim (syntax->datum #'dim)])
+         (with-syntax* ([(i     ...) (range dim)]
+                        [(d     ...) (generate-temporaries (make-list dim 'd))]
+                        [(ds    ...) (generate-temporaries (make-list dim 'ds))]
+                        [(d-min ...) (generate-temporaries (make-list dim 'd-min))]
+                        [(d-max ...) (generate-temporaries (make-list dim 'd-max))]
+                        [(d*    ...) (generate-temporaries (make-list dim 'd*))])
+           #'(let* ([coords (hash-keys grid)]
+                    [ds (map #{list-ref % i} coords)] ...
+                    [d-min (apply min ds)] ...
+                    [d-max (apply max ds)] ...)
+               (for*/fold ([grid* grid])
+                          ([d (in-range+ d-min d-max)] ...)
+                 (let* ([cube (hash-ref grid (list d ...) #\.)]
+                        [neighbours
+                         (for*/list ([d* (in-range+ d d)] ...
+                                     #:unless (and (= d d*) ...))
+                           (hash-ref grid (list d* ...) #\.))]
+                        [active-neighbours (actives neighbours)])
+                   (cond
+                     [(and (char=? cube #\#) (not (<= 2 active-neighbours 3)))
+                      (hash-set grid* (list d ...) #\.)]
+                     [(and (char=? cube #\.) (= active-neighbours 3))
+                      (hash-set grid* (list d ...) #\#)]
+                     [else grid*]))))))])))
+
+(define part1
+  (actives (hash-values ((iterate #{cycle 3 %} 6) (grid 3)))))
+
+(define part2
+  (actives (hash-values ((iterate #{cycle 4 %} 6) (grid 4)))))
+
+(show-solution part1 part2)