From fa1a39d1daacd14a37a0c47b4834a39ddad4466d Mon Sep 17 00:00:00 2001
From: hi <hi>
Date: Fri, 15 Aug 2025 10:10:20 +0000
Subject: [PATCH] verify graph path search

---
 Logic/Graph.hs | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/Logic/Graph.hs b/Logic/Graph.hs
index c45b3cd..ad86164 100644
--- a/Logic/Graph.hs
+++ b/Logic/Graph.hs
@@ -35,3 +35,21 @@ Just ["succ","succ","succ","succ","succ","succ","succ","succ","succ","succ"]
 ghci> bfs 13 0 (\x -> [("double", x+x), ("add", x+1)])
 Just ["add","double","add","double","double","add"]
 -}
+
+data VerifyPathError vertex edge
+  = NoSuchEdge vertex edge
+
+verifyPath
+  :: (Eq vertex, Ord vertex, Eq edge)
+  => GetEdges vertex edge
+  -> vertex
+  -> vertex
+  -> [edge]
+  -> Either (VerifyPathError vertex edge) Bool
+verifyPath getEdges goal start path =
+  case path of
+    [] -> Right $ start == goal
+    (thisEdge:nextEdges) ->
+      case map fst $ filter (\(next, realEdge) -> realEdge == thisEdge) $ getEdges start of
+        [] -> Left $ NoSuchEdge start thisEdge
+        (next:_) -> verifyPath getEdges goal next nextEdges