Add subdirectories

Add /ipynb/ and /py/ subdirectories to keep the home page neater.

py/parse.py

@@ -0,0 +1,52 @@
+grammar = {
+  'Noun': ['stench', 'wumpus'],
+  'Verb': ['is', 'smell'],
+  'Adjective': ['dead', 'smelly'],
+  'Adverb': ['left', 'back'],
+  'Pronoun': ['me', 'you'],
+  'Name': ['John', 'Mary'],
+  'Article': ['the', 'a'],
+  'Preposition': ['to', 'in'],
+  'Conjunction': ['and', 'or'],
+  'Digit': ['0', '1'],
+  
+  'S': [['NP', 'VP'], ['S', 'Comjunction', 'S']],
+  'NP': ['Pronoun', 'Noun', ['Article', 'Noun'], ['Digit', 'Digit'], 
+         ['NP', 'PP'], ['NP', 'RelClause']],
+  'VP': ['Verb', ['VP', 'NP'], ['VP', 'Adjective'], ['VP', 'PP'], 
+         ['VP', 'Adverb']],
+  'PP': [['Preposition', 'NP']],
+  'RelClause': [['that', 'VP']]
+  }
+  
+
+def parse(forest, grammar):
+    if len(forest) == 1 and category(forest[0]) == 'S':
+        return forest[0]
+    for i in range(len(forest)):
+        for lhs in grammar.keys():
+            for rhs in grammar[lhs]:
+		rhs = mklist(rhs)
+		n = len(rhs)
+		subsequence = forest[i:i+n]
+		if match(subsequence, rhs):
+                    print subsequence, lhs, '=>', rhs
+		    forest2 = forest[:]
+		    forest2[i:i+n] = [(lhs, subsequence)]
+		    result = parse(forest2, grammar)
+		    if result != None:
+			return result
+    return None
+
+def mklist(x):
+    if type(x) == type([]): return x
+    else: return [x]
+
+def match(forest, rhs):
+    for i in range(len(rhs)):
+        if category(forest[i]) != rhs[i] and forest[i] != rhs[i]: return 0
+    return 1
+
+def category(forest):
+    if type(forest) == type(()): return forest[0]
+    else: return 'word'