From 19ff0dd7d5081f3502cf2a58ead3ea22473e5fbb Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Carlos=20Mart=C3=ADn=20Nieto?= <cmn@dwim.me>
Date: Sat, 10 Aug 2013 06:30:49 +0200
Subject: [PATCH] Tree: raise an exception if we can't look up the tree

---
 lib/geef/tree.ex | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/lib/geef/tree.ex b/lib/geef/tree.ex
index 474ecfb..fcbcea2 100644
--- a/lib/geef/tree.ex
+++ b/lib/geef/tree.ex
@@ -44,8 +44,15 @@ defimpl Access, for: Geef.Tree do
 
 end
 
+defexception Geef.TreeError, reason: nil do
+  def message(Geef.TreeError[reason: reason]) do
+    "tree error #{inspect reason}"
+  end
+end
+
 defimpl Enumerable, for: Geef.Tree do
   alias Geef.Tree
+  alias Geef.TreeError
 
   def count(tree) do
     Tree.count(tree)
@@ -67,8 +74,12 @@ defimpl Enumerable, for: Geef.Tree do
 
   # Call the user-passed function and recurse with the next index
   defp reduce(tree, idx, count, acc, fun) do
-    cur = Tree.nth(tree, idx)
-    reduce(tree, idx + 1, count, fun.(cur, acc), fun)
+    case Tree.nth(tree, idx) do
+      {:ok, entry} ->
+        reduce(tree, idx + 1, count, fun.(entry, acc), fun)
+      {:error, error} ->
+        raise TreeError, reason: error
+    end
   end
 
 end