.

wcfs/internal/xbtree.py

@@ -25,18 +25,52 @@ It is primarily used to verify ΔBTail in wcfs.
 
 - `Tree` represents a tree node.
 - `Bucket` represents a bucket node.
-- `StrctureOf` returns internal structure of a BTree represented as Tree and
+- `StructureOf` returns internal structure of a BTree represented as Tree and
   Bucket nodes.
 - `Restructure` XXX
 
-- GenStructs
+- `AllStructs` XXX
+
 
 Topology encoding
 -----------------
 
-XXX Typology:
-- TopoEncode XXX
-- TopoDecode
+Topology encoding provides way to represent structure of a Tree as path-like string.
+
+TopoEncode converts Tree into its topology-encoded representation, while
+TopoDecode decodes topology-encoded string back into Tree.
+
+The following example illustrates topology encoding represented by string
+"T3/T-T/B1-T5/B-B7,8,9":
+
+      [ 3 ]             T3/         represents Tree([3])
+       / \
+     [ ] [ ]            T-T/        represents two empty Tree([])
+      ↓   ↓
+     |1|[ 5 ]           B1-T5/      represent Bucket(1) and Tree([5])
+         / \
+        || |7|8|9|      B-B7,8,9    represents empty Bucket() and Bucket(7,8,9)
+
+
+Topology encoding is specified as follows:
+
+A Tree is encoded by depth-order traversal, delimiting layers with "/".
+Inside a layer Tree and Bucket nodes are signalled as
+
+    "T<keys>"       ; Tree
+    "B<keys>"       ; Bucket
+
+Keys are represented as ","-delimited list of integers. For example Tree
+with [1,3,5] keys is represented as
+
+    "T1,3,5"        ; Tree([1,3,5])
+
+Nodes inside one layer are delimited with "-". For example a layer consisting
+of an empty Tree, a Tree with [1,3] keys, and Bucket with [4,5] keys is
+represented as
+
+    "T-T1,3-B4,5"   ; layer with Tree([]), Tree([1,3]) and Bucket([4,5])
+
 """
 
 from __future__ import print_function, absolute_import
@@ -140,15 +174,11 @@ def StructureOf(node):
     panic("unknown node type %r" % typ)
 
 
-# TypoEncode returns topology encoding for internal structure of the tree.
+# TopoEncode returns topology encoding for internal structure of the tree.
 #
 # See top-level docstring for what topology is.
-def TypoEncode(tree):
-    treeStruct = StructureOf(tree)
-    return topoEncode(treeStruct)
-
-def topoEncode(treeStruct):
-    1/0
+def TopoEncode(tree):
+    assert isinstance(tree, Tree)
 
 
 # TopoDecode decodes topology-encoded text into Tree structure.
@@ -166,7 +196,7 @@ def Restructure(tree, newStructure):
     1/0
 
 # AllStructs generates subset of all possible BTree structures for BTrees with
-# specified keys and btree depth up-to maxdepth. Eatch tree node is split by
+# specified keys and btree depth up-to maxdepth. Each tree node is split by
 # up-to maxsplit points.
 def AllStructs(keys, maxdepth, maxsplit): # -> i[] of Tree
     assert isinstance(maxdepth, int); assert maxdepth >= 0

wcfs/internal/xbtree_test.py

@@ -25,7 +25,7 @@ from wendelin.wcfs.internal import xbtree
 from BTrees.LOBTree import LOBTree
 from BTrees.tests import testBTrees
 
-def test_topologyOf():
+def test_structureOf():
     T = xbtree.Tree
     B = xbtree.Bucket
 
@@ -73,6 +73,10 @@ def test_topologyOf():
                                      (((), ()),  (6, 10)),
     """
 
+
+def test_topoEncoding():
+    1/0
+
 def test_AllStructs():
     T = xbtree.Tree
     B = xbtree.Bucket