State Monad in F#

I watched Brain Beckman's Web Cast "The Zen of Stateless State"
http://channel9.msdn.com/shows/Going+Deep/Brian-Beckman-The-Zen-of-Expressing-State-The-State-Monad/
and wrote example code for State Monad in F#. Please Check
http://www.paul-abraham.com/MonadsInFSharp.doc