modifyPrevTokens :: ((Maybe Token, Maybe Token) -> (Maybe Token, Maybe Token)) -> Alex ()
modifyPrevTokens f = modifyUserState $ \us -> us { prevTokens = f (prevTokens us) }
modifyPrevTokens :: ((Maybe Token, Maybe Token) -> (Maybe Token, Maybe Token)) -> Alex ()
modifyPrevTokens f = modifyUserState $ \us -> us { prevTokens = f (prevTokens us) }
modifyPrevTokens f = modifyUserState $ \us -> us { prevTokens = f (prevTokens us) }