Here's another reason why I think it's better to make the monad used variable (as with my framework but not Malcolm's). The main method I use for encoding binary data needs access to a bit of extra information about what it is encoding it for. This basically can't be done within Malcolm's framework except by, er, parking the extra stuff in a global variable and then using another global lock as otherwise hell will pop when two threads try to use this mechanism at once. It can be done within my framework, though you need to change it slightly to make the monad in question one of the class variables. Thus you would have class HasBinary a monad Most types (integers, lists and so on) would just instance this for all values of monad. Where you need extra state you would create an extra monad for the purpose, and just instance for that monad. This is sufficiently worthwhile to me that I think I shall probably implement it, and then see whether anyone else is interested in using it. I don't think you need any extensions apart from FFI and multi-parameter type-classes, AND some way of writing/reading CChars and CStringLen's to Handles, how do I do this please Simon? hPutChar/hGetChar/hPutBuf/hGetBuf?