class instance with nested types

[Matthias Höchsmann]

Hello,   I have the following problem:   basic datatypes   > type Sequence a = [a] > data Tree a = N a (Forest a) deriving (Ord,Eq,Show) > type Forest a = Sequence (Tree a)   i want to construct a class Xy   > class Xy s a where >      test :: s a -> a   and make an instance for list of characters   > instance Xy [] Char where >      test [a] = a   this works, and an instance for a forest and tried something like this   > instance  ([] Tree) Char where > test x@(N a xs):txs = a   I get illegal type errors. Is it possible to use nested types in a class ?   Hope you can help me Matthias