Re: Type signature inside an instance declaration

"Kwanghoon Choi" wrote:

===================================================================== instance Arg a => Arg [a] where pr _ = "[" ++ pr (undefined :: a) ++ "]" =====================================================================

You want to use `asTypeOf`, with a lazy pattern to name a value of type 'a'. pr xs = "[" ++ pr (undefined `asTypeOf` x) ++ "]" where (x:_) = xs or pr ~(x:_) = "[" ++ pr (undefined `asTypeOf` x) ++ "]" Regards, Malcolm