Haskell has a few libraries that do this[1]. Not trying to one-up the article or anything, just thought you might be interested to see that there are other places where this is available, and that it's not even something that needs full language support in some cases, just a library. Also similar - you can pretty transparently model nondeterminism[2] and probability[3] on a "promise"-like interface with just a library. Of course, whether or not there's good documentation is another story.
[1] https://stackoverflow.com/questions/19598906/is-there-a-valu... [2] https://stackoverflow.com/questions/20638893/how-can-non-det... [3] http://wiki.haskell.org/Probabilistic_Functional_Programming