Simon Peyton-Jones schrieb:
I was under the impression that the main reason GHC requires .hs-boot files is that nobody has had the time or inclination to make it resolve circular dependencies automatically, and not an intentional design decision to encourage "good design".
Indeed. I’ve added some notes here http://hackage.haskell.org/trac/ghc/ticket/1409#comment:37
When reading this, I'm afraid adding this feature will cause more bugs than features. For me, generally working hs-boot-files would be enough, that is, hs-boot files that support all situations of mutually depending classes and instances. I still prefer non-circular modules, because I understand their relationship more easily. I prefer to explicitly state when I want cyclic imports, as I currently do with hs-boot files. As time went by, I become familiar with the discussed methods of avoiding import cycles and actually, all packages I have written so far do not contain any circular import and thus no hs-boot file.