Currently in the c++ developers ml, there's a discussion of a proposed Expected<T> or an Either<L,R> template: http://article.gmane.org/gmane.comp.lib.boost.devel/242496 A lot of the discussion appears, at least to me, to not be aware of how haskell handles similar situations. The above link was to my post suggesting they try to emulate the way haskell solves the problem using Monads. However, I've only briefly dabbled in haskell; hence, my responses on that thread are probably missing something. I invite anyone on this list to please provide insights on this particular thread in the boost.devel mailing list. -kind regards, Larry