shortest path racket version

shortetpath.rkt

#lang racket
(require "../connive/connive.rkt")

;; :: (state -> [state]), (state -> Bool), state -> [state]
(:= (blocking-path get-successors goal? start)
    
    ;; :: (set state), [state] -> #f | [state]
    (:== solution (blocked path) 
         (_ (cons (list state info) prevs)) 
         (?? (goal? (list state info)) (reverse path)
             (lyt (now-blocked (set-add blocked state))
                  (first-solution  now-blocked path (<- s s (get-successors (list state info))
                                                        (not (set-member? now-blocked (first s))))))))
    
    ;; :: (set state), [state], [state] -> #f | [state]                            
    (:== first-solution (blocked path states) 
         (_ _ empty) #f
         (_ _ (cons state states)) (or (solution blocked (cons state path))
                                       (first-solution blocked path states))) 
    
    (solution (set) (list start)))