[Haskell-cafe] Fixed length list type?

Does anyone know of a hackage package that has fixed length list type that is an instance of Applicative, Foldable and Traversable? (a list type that somehow encodes its length in the type) I've found lots of fixed length list types, but non that are members of the common typeclasses. I've implement one here: http://github.com/jvranish/FixedList/blob/6c861a12ba5d17481fd22cdb1f90404abf... But am I just duplicating work that is already out there? Thanks, - Job