Re: class instance with nested types

On Fri, 27 Oct 2000, Matthias Höchsmann wrote:

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

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class Xy s a where test :: s a -> a

and make an instance for list of characters

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instance Xy [] Char where test [a] = a

this works, and an instance for a forest and tried something like this

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instance ([] Tree) Char where test x@(N a xs):txs = a

Don't you mean test (N a xs:txs) = a ? /Lars L