Pretty funny to read your post since it has basically been my train of thoughts :)

In the end I haven’t used monads, but have implemented a way to chain commands (like promises but synchronous of course).

here the github link: https://github.com/apneadiving/waterfall

or more sexy: http://slides.com/apneadiving/code-ruby-like-you-build-legos

I would be curious to have your thoughts about it! :)