diff --git a/analyze_structure.lua b/analyze_structure.lua
index ea074ac..c9f49fa 100644
--- a/analyze_structure.lua
+++ b/analyze_structure.lua
@@ -181,29 +181,32 @@ end
 
 --------------------------------------------------------------------------------
 
-local function visit_table (t, info, visited)
+local function analyze_structure (root)
+    assert(type(root) == 'table')
 
-    -- Who've been visited? Bookkeeping
-    visited[t] = (visited[t] or 0) + 1
-    if visited[t] == 2 then
-        info[t].marker, info.next_mark = info.next_mark, info.next_mark + 1
+    local info, visited, next_mark, depth  =  { root = root }, {}, 1, { [root] = 0 }
+    local queue  =  { root, bottom = 1, top = 2 }
+
+    while queue.bottom < queue.top do
+        queue.bottom  =  queue.bottom + 1
+        local node        =  queue[queue.bottom-1]
+        -- Who've been visited? Bookkeeping
+        visited[node] = (visited[node] or 0) + 1
+        if visited[node] == 2 then
+            info[node].marker, next_mark  =  next_mark, next_mark + 1
+        end
+        -- Get table info & visit children.
+        if visited[node] < 2 then
+            info[node] = get_table_info(node)
+            info[node].depth  =  depth[node]
+            for k, v in pairs(node) do
+                if type(k) == 'table' then  queue[queue.top], queue.top, depth[k]  =  k, queue.top + 1, depth[node] + 1  end
+                if type(v) == 'table' then  queue[queue.top], queue.top, depth[v]  =  v, queue.top + 1, depth[node] + 1  end
+            end
+        end
     end
-    if visited[t] >= 2 then  return  end
 
-    -- Get table info
-    info[t] = get_table_info(t)
-
-    -- Visit children.
-    for k,v in pairs(t) do
-        if type(k) == 'table' then visit_table(k, info, visited) end
-        if type(v) == 'table' then visit_table(v, info, visited) end
-    end
-end
-
-local function analyze_structure (t)
-    local info, visited = { root = t, next_mark = 1 }, {}
-    visit_table(t, info, visited)
-    info.next_mark = nil
+    assert(type(info) == 'table')
     return info
 end