I say it is can be more difficult in the sense I don't know if it is as simple as invoking an interceptor in Parser.run. abailly's solution (which is very similar to the one I implemented some time ago, that's why I submitted the little patch) has the advantage of not being intrusive with the existing codebase : combinating a new parser, isn't it the nature of JParsec ?

If you fell you can easily implement a far more elegant solution, then submit your patch...