What can the Haskell package category-extras be used for? See here. Has anyone attempted to use this to verify category theoretic proofs? Given the relationship between categories and graphs, are there some applications with respect to graph algorithms? What other possible uses are there for this package and those associated with it?

I realize this is a broad, open-ended question, which may not be entirely appropriate for Stack Exchange. A better place to post this question could also be a helpful answer.
This library is not especially useful for category-theoretic proofs, since Haskell's typechecking is not sufficient to verify that the constructions satisfy the required properties. Surprisingly enough ;), it's actually intended to be used for writing Haskell programs. You are best off asking on the Haskell-cafe mailing list for examples.