Debugs a buggy implementation of Dijkstra’s algorithm.


(module dijkstra mzscheme
  (require "dijkstra-solver.ss"
           (lib "list.ss"))
  (print-struct #t)
  (define g (make-graph 'directed))
  (define (m-node label x y) (make-node label x y +inf.0))
  (define nodes
     (m-node 'J 200 100)
     (m-node 's 100 125)
     (m-node '1 150 100)
     (m-node '2 150 150)
     (m-node '4 250 100)
     (m-node '5 300 100)
     (m-node '6 300 150)))
  (for-each (lambda (n) (graph-node-add! g n)) nodes)
  (define (n-ref label) 
    (first (filter (lambda (n) (eq? label (node-label n))) nodes)))
  (define edges
    (list  (list (n-ref 's) (n-ref '1))
           (list (n-ref 's) (n-ref '2))
           (list (n-ref '1) (n-ref 'J))
           (list (n-ref '4) (n-ref '5))
           (list (n-ref 'J) (n-ref '4))
           (list (n-ref 'J) (n-ref '6))))
  (for-each (lambda (e) (graph-edge-add! g (first e) (second e)))
  (printf "~n~n---output from dijkstra.ss:~n~a~n---~n"
          (solve g (reverse nodes) (n-ref 's))))


(require "dijkstra-solver.ss"
         (lib "match.ss"))

(define-mztake-process p
                       ("heap.ss" [inserts 49 6 bind 'item]
                                  [removes 67 10 bind 'result]))

(define (not-in-order e)
     [('reset _) false]
     [(_ 'reset) false]
     [(previous current) (> previous current)]
     [else false])
   (history-e 2 e)))

(define inserts-and-removes-e (merge-e (removes . ==> . node-weight)
                                       (inserts . -=> . 'reset)))
(define violations (not-in-order inserts-and-removes-e))

(printf-b "all inserts and removes: ~a" (history-b inserts-and-removes-e))
(printf-b "all violations: ~a" (history-b violations))
(printf-b "latest-violation: ~a" (hold violations))

#| Implementation of the local model follows... |#
(define ((insert-in-model item) model)
  (printf "~nInserting ~a into model containing:~n~a~n" item (value-now model))
  (cons item model))

(define ((remove-from-model item) model)
  (printf "~nRemoving ~a from model containing:~n~a~n" item (value-now model))
  (filter (lambda (i) (not (equal? i item))) model))

(define inserters (accum-b (inserts . ==> . insert-in-model) empty))
(define removers  (accum-b (removes . ==> . remove-from-model) inserters))

(start/resume p)