These are the minimum required fixes to get greencard building under GHC 7.10. As noted in the comments around the existing Functor instances, though, this may cause compatibility issues with earlier compilers and indeed other, non-GHC Haskell 98 compilers. I am submitting this commit not with a view to having it accepted as is but as a starting-point for a conversation about how to move forward with supporting the latest GHC alongside earlier versions.
This issue appears to be discussing a feature request or bug report related to the repository. Based on the content, it seems to be still under discussion. The issue was opened by dpwright and has received 3 comments.