Experimental parser: build regex parse trees for all rules

tools/lexer_generator/transition_keys.py

Index: tools/lexer_generator/transition_keys.py
diff --git a/tools/lexer_generator/transition_keys.py b/tools/lexer_generator/transition_keys.py
index a68ea30f527f8ce3e508be321adeefb211a03a1a..8ddbfb3b073f770ab3740b0d0b331b0345782053 100644
--- a/tools/lexer_generator/transition_keys.py
+++ b/tools/lexer_generator/transition_keys.py
@@ -103,12 +103,12 @@ class TransitionKey:
       elif graph[1] == 'lit':
         ranges.append(TransitionKey.__unicode_literal_bounds)
       else:
-        assert "unknown character class %s" % graph[1]
+        raise Exception("unknown character class [%s]" % graph[1])
     elif key == 'CAT':
       for x in [graph[1], graph[2]]:
         TransitionKey.__process_graph(x, ranges)
     else:
-      assert False, "bad key %s" % key
+      raise Exception("bad key [%s]" % key)
 
   @staticmethod
   def character_class(invert, graph):