It would be so useful if we could get monads in boost mpl (possibly for boost.preprocessor & boost.fusion aswell). I've tired to attempting a general solution for boost mpl but i keep hitting a snag, it's due to the fact that metafunction arguments are essentially untyped, it just confuses the hell out of me since i'm so use to the typeful approach in haskell. So i'm wondering if you guys could help me out, here are two links that implement monads in Scheme: http://groups.google.com/group/comp.lang.functional/msg/2fde5545c6657c81 http://okmij.org/ftp/Scheme/monad-in-Scheme.html This might be useful in help us out in implementing them in boost mpl (due to the fact of scheme's untyped nature).