.

wcfs/internal/xbtree.py

@@ -26,12 +26,16 @@ It is primarily used to verify ΔBTail in wcfs.
 XXX Typology:
 """
 
-# Tree represents internal tree node.
+from BTrees import check as bcheck
+
+# Tree represents a tree node.
 class Tree:
     #   .keyv       () of keys
     #   .children   () of children  len(.children) == len(.keyv) + 1
     def __init__(tree, keyv, *children):
-        assert len(children) == len(keyv) + 1
+        assert len(children) == len(keyv) + 1, (keyv, children)
+        # XXX assert keyv ↑
+        # XXX assert children keys consistent?
         tree.keyv     = tuple(keyv)
         tree.children = tuple(children)
 
@@ -45,7 +49,20 @@ class Tree:
 
 # StructureOf returns internal structure of the tree.
 def StructureOf(tree):
-    1/0
+    typ = type(tree)
+    assert "Tree" in typ.__name__, typ
+
+    kind, keys, children = bcheck.crack_btree(tree, True)
+    if kind == bcheck.BTREE_EMPTY:
+        return Tree([])
+    if kind == bcheck.BTREE_ONE:
+        return Tree([])
+    if kind == bcheck.BTREE_NORMAL:
+        return Tree(keys, *[StructureOf(_) for _ in children])
+
+    panic("bad kind %r" % kind)
+
+
 
 # TypologyOf returns topology encoding for internal structure of the tree.
 #