[Twisol]

> you really need to use haskell.

Or Scala. They're the only two common-use languages I'm aware of whose type systems are expressive enough to define what a monad (or a category, or a ...) is internally. Of course you can identify particular monads (or ...) in any language, but you can't talk about them inside most languages.

[larve]

C++ fits the bill as well (!)

I wager that you can get pretty far with compile-time macros, even as rudimentary as C's, to encoder a fair bit of generic monad machinery.