+ -- | The error message we return if unpickling fails.
+ --
+ errmsg = "Could not unpickle " ++ dtd ++ "."
+
+ -- | Try to migrate and import using the given pickler @f@;
+ -- if it works, return the result. Otherwise, return an
+ -- 'ImportFailed' along with our error message.
+ --
+ go f = maybe
+ (return $ ImportFailed errmsg)
+ migrate_and_import
+ (unpickleDoc f xml)
+