hvr/deepseq-generics — pull request #1 by jkoppel (2013-09-14 01:07:16+00:00)
Title: Providing a GNFData instance for V1

Although V1 is uninhabited, the lack of an instance for V1 prevents GHC from inferring an instance for types such as (U1 :+: V1), which very much is inhabited. I've encountered types like that when creating Generic instances for certain GADTs.