--- a/python/pyburg.py	Mon Jan 27 19:58:07 2014 +0100
+++ b/python/pyburg.py	Thu Jan 30 19:03:24 2014 +0100
@@ -245,8 +245,8 @@
         self.print('    def gen(self, tree):')
         self.print('        self.burm_label(tree)')
         self.print('        if not tree.state.has_goal("{}"):'.format(self.system.goal))
-        self.print('          raise Exception("Tree not covered")')
-        self.print('        self.apply_rules(tree, "{}")'.format(self.system.goal))
+        self.print('          raise Exception("Tree {} not covered".format(tree))')
+        self.print('        return self.apply_rules(tree, "{}")'.format(self.system.goal))
 
     def emit_record(self, rule, state_var):
         # TODO: check for rules fullfilled (by not using 999999)