[Haskell-cafe] Constraint on data type

[Vlatko Basic]

Hi Cafe,

I have these typeclasses defined:

     class UA a where ...
     class RA a where ...

and this data definition

     data (UA u, RA r) => AD u r = AD { ... }

I have another data definition

     data ACT aur c = ACT { x :: aur, ... }

but the type 'aur' should be restricted to (AD u r) only.
(I would like to keep 'aur' as 1 parameter, not as
     data ACT u r c = ACT { x :: AD u r, ... } )


How can such constraint be defined?


Best regards,

vlatko