From a40b1ec187ee44c7c562136cc43a74185a3a992d Mon Sep 17 00:00:00 2001
From: Sergiu Ivanov <sivanov@colimite.fr>
Date: Sun, 31 Oct 2021 20:57:17 +0100
Subject: [PATCH] Add bfs/generalized.

---
 graph.rkt | 38 ++++++++++++++++++++++++++++++++++++--
 1 file changed, 36 insertions(+), 2 deletions(-)

diff --git a/graph.rkt b/graph.rkt
index 65e1d24..445ea85 100644
--- a/graph.rkt
+++ b/graph.rkt
@@ -19,7 +19,8 @@
 ;;; https://stackoverflow.com/questions/65386334/racket-generic-graph-library-in-typed-racket
 
 (module graph-wrapper racket
-  (require (prefix-in g: graph))
+  (require (prefix-in g: graph)
+           data/gen-queue/fifo)
   (provide (struct-out graph) has-vertex? has-edge? vertex=? add-vertex! remove-vertex!
            rename-vertex! add-edge! add-directed-edge! remove-edge!
            remove-directed-edge! get-vertices in-vertices get-neighbors
@@ -32,7 +33,7 @@
            undirected-graph directed-graph
            matrix-graph?
 
-           bfs fewest-vertices-path
+           bfs bfs/generalized fewest-vertices-path
            dfs dfs/generalized
 
            graphviz)
@@ -115,6 +116,26 @@
   ;; 4.1 Breadth-first Search
   (define (bfs g source)
     (g:bfs (gg g) source))
+  (define (bfs/generalized
+           g
+           source
+           #:init-queue [init-queue (mk-empty-fifo)]
+           #:break [break? (λ (G source from to) #f)]
+           #:init [init void]
+           #:visit? [custom-visit?-fn (λ (G source from to) #f)]
+           #:discover [discover (λ (G s u v acc) acc)]
+           #:visit [visit (λ (G s v acc) acc)]
+           #:return [finish (λ (G s acc) acc)])
+    (g:bfs/generalized
+     (gg g)
+     source
+     #:init-queue init-queue
+     #:break break?
+     #:init init
+     #:visit? custom-visit?-fn
+     #:discover discover
+     #:visit visit
+     #:return finish))
   (define (fewest-vertices-path G source target)
     (g:fewest-vertices-path (gg G) source target))
 
@@ -201,6 +222,15 @@
   ;; 4.1 Breadth-first Search
   [bfs (-> Graph Any (Values (Mutable-HashTable Any Number)
                              (Mutable-HashTable Any Any)))]
+  [bfs/generalized (->* (Graph Any)
+                        (#:init-queue Any ; TODO: Add a proper type.
+                         #:break (-> Graph Any Any Any Boolean)
+                         #:init (-> Graph Any Void)
+                         #:visit? (-> Graph Any Any Any Boolean)
+                         #:discover (-> Graph Any Any Any Any Any)
+                         #:visit (-> Graph Any Any Any Any)
+                         #:return (-> Graph Any Any Any))
+                        Any)]
   [fewest-vertices-path (-> Graph Any Any (U (Listof Any) False))]
 
   ;; 4.2 Depth-first Search
@@ -301,6 +331,10 @@
     (define-values (bfs-lens bfs-tree) (bfs (directed-graph '((a b) (b c))) 'a))
     (check-equal? (hash->ordered-list bfs-lens) '((a . 0) (b . 1) (c . 2)))
     (check-equal? (hash->ordered-list bfs-tree) '((a . #f) (b . a) (c . b)))
+
+    (check-equal? (bfs/generalized (directed-graph '((a b) (a c) (b d) (c d))) 'a)
+                  (void))
+
     (check-equal? (fewest-vertices-path (directed-graph '((a b) (b c) (c d))) 'a 'd)
                   '(a b c d))