Implement eq/hash for Rule (Issue #278)

lark/grammar.py

@@ -51,6 +51,13 @@ class Rule(object):
     def __repr__(self):
         return 'Rule(%r, %r, %r, %r)' % (self.origin, self.expansion, self.alias, self.options)
 
+    def __hash__(self):
+        return hash((self.origin, tuple(self.expansion)))
+    def __eq__(self, other):
+        if not isinstance(other, Rule):
+            return False
+        return self.origin == other.origin and self.expansion == other.expansion
+
 
 class RuleOptions:
     def __init__(self, keep_all_tokens=False, expand1=False, priority=None):