RE: [Haskell-cafe] Consequences of newtype deriving implementation w.r.t. base classes

| I just noticed some unexpected consequences of the way newtype deriving | is implemented in GHC. Because the dictionary of the underlying type is | reused, so are base classes. This message is a literate Haskell program | illustrating the problem. Excellent point. | As a solution I would suggest that newtype deriving a class instance is | only allowed if all base classes instances are also derived using | newtype deriving. This presents problems for Show and Read, because they | cannot be derived in that way. It will, however, catch problems with | most other classes. Yes, I think you are right. I'll make a Trac bug report for it; but I think I'll fix it in the HEAD only. S