So let me ask this question a different way. Is it possible to use Read/Show or Typeable with Existential types. Given MyClass and MyType as follows: class (Read a,Show a,Typeable)=>MyClass a where foo::a type MyType = forall a. MyClass a=> [a] Is there a way to persist MyType? My suspicion is that there isn't because Haskell knows how to say that a string can't be parsed into a particular type but it does not know how to say that a string can't be parsed into any type that is an instance of a particular class. So, assuming you can't I amn curious to know know if this is an in-principle problem or just an in-fact problem. -Alex- _________________________________________________________________ S. Alexander Jacobson mailto:me@alexjacobson.com tel:917-770-6565 http://alexjacobson.com