maze-conversion.rkt

(require "../ncurses/api.rkt")
(require "struct.rkt")
(require data/pvector)
(require data/collection)
(require lens)

(define WIDTH 2)
(define HEIGHT 2)

(define NORTH 1)
(define SOUTH 2)
(define EAST 4)
(define WEST 8)

(define DX (hash EAST 1 WEST -1 NORTH 0 SOUTH 0))
(define DY (hash EAST 0 WEST 0 NORTH -1 SOUTH 1))
(define OPPOSITE (hash EAST WEST WEST EAST NORTH SOUTH SOUTH NORTH))

(define (carve-passages-from cx cy grid)
  (define directions (sort (list NORTH SOUTH EAST WEST)
			   <
			   #:key (λ (x) (random))
			   #:cache-keys? #t))
  (for/fold ([grid grid])
    	    ([direction directions])
    (define nx (+ cx (hash-ref DX direction)))
    (define ny (+ cy (hash-ref DY direction)))
    (cond
      [(and (<= 0 ny (sub1 (length grid)))
	    (<= 0 nx (sub1 (length (nth grid ny))))
	    (= 0 (nth (nth grid ny) nx)))
       (define grid^ (lens-transform (pvector-ref-nested-lens cy cx)
				     grid
				     (curry bitwise-ior direction)))
       (define grid^^ (lens-transform (pvector-ref-nested-lens ny nx)
				      grid^ 
				     (curry bitwise-ior (hash-ref OPPOSITE direction))))
       (carve-passages-from nx ny grid^^)]
      [else
	grid])))

(carve-passages-from 0 0 (make-pvector HEIGHT (make-pvector WIDTH 0)))