a-star.rkt

#lang racket
(require racket/set)
(define (pq-inserts elems pq)
  (sort (append elems pq) (lambda (a b)
    ((first a) . < . (first b)))))
(define (a-star estimate neighbors dist eps start)
  (define (go visited pq)
    (match pq
      [(list* (list estimation distance path) rest-pq)
        (let ((point (first path)))
          (if ((estimate point) . <= . eps)
            path
            (let*
              ( (near
                  (filter
                    (compose not (curry set-member? visited))
                    (neighbors point)))
                (paths
                  (for/list ([pt near])
                    (let ((distance1 (+ distance (dist point pt))))
                      (list
                        (+ distance1 (estimate pt))
                        distance1
                        (list* pt path))))))
              (go
                (set-add visited point)
                (pq-inserts paths rest-pq)))) )]
      [else
        '()]))
  (define initial
    (list (list 0 0 (list start))))
  (reverse
    (go
      (set)
      initial)))

Hi, Thank you so much for your post and code! I do wonder however how to run this code on some points to test it . how do I define the list with obstacles and path and see the result?? Thanks again