Hi, monad-embed is an experimental programming language that parameterizes everything on a monad by default. Examples, source code, etc. are at http://timmaxwell.org/pages/monad-embed/. I posted about it on the Haskell subreddit a few months ago (see http://bit.ly/cUZvrB) but I was advised to re-post it in haskell-cafe as well. Tim Maxwell