Could ReadP's '+++' (symmetric choice) operator be implemented for all Monads with the 'interleave' function mentioned in Backtracking, Interleaving, and Terminating Monad Transformers<http://portal.acm.org/ft_gateway.cfm?id=1086390&type=pdf&coll=GUIDE&dl=GUIDE&CFID=5430836&CFTOKEN=76321932>? This paper was a tough read for me, but it looks like they solve the same problem, but one interleaves computations within a monad and the other does it from the outside. Or am I just confused? Thanks, Greg