fix #1 Fixed bug with memoization cache not being cleared on input change.

arpeggio/__init__.py

@@ -102,6 +102,23 @@ class ParsingExpression(object):
         else:
             return id(self)
         
+    def clear_cache(self, processed=None):
+        '''
+        Clears memoization cache. Should be called on input change.
+        
+        Args:
+            processed (set): Set of processed nodes to prevent infinite loops.
+        '''
+        
+        self.result_cache = {}
+        if not processed:
+            processed = set()
+        
+        for node in self.nodes:
+            if node not in processed:
+                processed.add(node)        
+                node.clear_cache(processed)
+                
     def _parse_intro(self, parser):
         logger.debug("Parsing %s" % self.name)
         results = []
@@ -561,6 +578,7 @@ class Parser(object):
         self.nm = None  # Last NoMatch exception
         self.line_ends = []
         self.input = _input
+        self.parser_model.clear_cache()
         self.parse_tree = self._parse()
         return self.parse_tree