From 417bbaab5bdcd277ed4b3805be15613f82a61bdc Mon Sep 17 00:00:00 2001
From: Kui Tang <kuitang@gmail.com>
Date: Sun, 17 Jul 2011 21:30:53 -0400
Subject: [PATCH] working symboltable and topsort

---
 flowconduit/symboltable.py | 21 +++++++++++-------
 flowconduit/topsort.py     | 45 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 58 insertions(+), 8 deletions(-)
 create mode 100644 flowconduit/topsort.py

diff --git a/flowconduit/symboltable.py b/flowconduit/symboltable.py
index caaf783..b44096b 100644
--- a/flowconduit/symboltable.py
+++ b/flowconduit/symboltable.py
@@ -4,22 +4,27 @@
 Based on http://code.activestate.com/recipes/577434-nested-contexts-a-chain-of-mapping-objects/
 """
 
-from collections import Mapping
+from collections import Mapping, Iterable
 from itertools import chain, imap
 
 class SymbolTable(dict):
-    def __init__(self, parent=None):
+    def __init__(self, parents=None):
         'Create a new root context.'
-        self.parent = parent
-        self.map    = {}
-        self.maps   = [ self.map ]
-        if parent is not None:
+        self.parents = parents
+        self.map     = {}
+        self.maps    = [ self.map ]
+        if parents is not None:
             # Remember, it's a list of pointers.
-            self.maps += parent.maps
+            added = set()
+            for p in parents:
+                for m in p.maps:
+                    if id(m) not in added:
+                        added.add(id(m))
+                        self.maps.append(m)
 
     def new_child(self):
         'Make a child context.'
-        return self.__class__(parent=self)
+        return self.__class__(parents=[ self ])
 
     def root(self):
         return self if self.parent is None else self.parent.root
diff --git a/flowconduit/topsort.py b/flowconduit/topsort.py
new file mode 100644
index 0000000..4fa37e4
--- /dev/null
+++ b/flowconduit/topsort.py
@@ -0,0 +1,45 @@
+# Based on CLRS 3rd ed, 613
+# 
+
+from itertools import chain
+from functools import reduce
+from collections import deque, defaultdict
+
+intern('gray')
+intern('black')
+
+class TopsortState(object):
+    def __init__(self):
+        self.visited = {}
+        self.result  = deque()
+
+class CycleError(Exception): pass
+
+def dfs(adj, state):
+    #verts = chain(adj.iterkeys(), *adj.itervalues())
+    # TODO: Figure out the generator
+    verts = chain((j for i in adj.values() for j in i), adj.keys())
+    for u in verts:
+        if u not in state.visited: dfs_visit(adj, u, state)
+
+def dfs_visit(adj, u, state):
+    state.visited[u] = 'gray'
+    for v in adj[u]:
+        if v not in state.visited: dfs_visit(adj, v, state)
+        elif state.visited[v] == 'gray':
+            raise CycleError("Cycle with edge (%s, %s) detected."%(u,v))
+    state.visited[u] = 'black'
+    state.result.appendleft(u)
+
+def topsort(adj):
+    state = TopsortState()
+    dfs(adj, state)
+    del state.visited
+    return state.result
+
+def topsort_from_src(adj, src):
+    state = TopsortState()
+    dfs_visit(adj, src, state)
+    del state.visited
+    return state.result
+