Hi all, I'm [trying to] develop a system that uses plug-ins to implement a "black-box" ADT, that is a data-type and a few typeclass instances for it. I want my system (a theorem prover) to be able to work with any of these plug-ins (which define a logic and operations on its formulae) but have been having trouble. I've had a go at using forall's, and at adding a type variable (constrained to the appropriate class) to the interface of the plug- in, but I haven't been able to get it to work and have run out of ideas. Is it possible to define data-types in a module loaded at run-time with hs-plugins and have values pass out of the plug-in (though only being used by functions within it)? Can someone point me in the right direction? Cheers, Thomas Sutton