hub.darcs.net :: jtapolczai -> transformers -> changes

These instances were added in base-4.9 (see http://git.haskell.org/ghc.git/commit/5097f3802124cfbe6810bff8110df91d4c52096b)

These instances were added in base-4.9 (see http://git.haskell.org/ghc.git/commit/8b57cac5974c9fffccbcae3104b5b5d18760749e)

(suggested by Oliver Charles)

It seems it was buggy in 6.12.

These instances were added to base-4.9.0.0

As a part of #11135. This conditionally exposes Data.Functor.Classes, Data.Functor.Compose, Data.Functor.Product, and Data.Functor.Sum if using GHC 7.10 or earlier. This also backports Typeable, Data, Generic, and Generic1 instances that will be introduced in base-4.9.0.0 (GHC 8.0).

Now there are two methods in each class, corresponding to the methods in the basic classes, and each of the lifting functions takes pairs of function arguments. The lifting functions (which have not appeared in any release) are renamed from xxxWith to liftXxx, to avoid a clash with showListWith (from Text.Show).

The Read1 and Show1 classes did not allow special cases for lists as supported by the base classes Read and Show. Thus for example the following displayed incorrectly:

Backwards "abc" Compose (Just "abc")

see also https://ghc.haskell.org/trac/ghc/ticket/11135

To fix this requires an extra argument to the methods in Read1 and Show1, effectively taking explicit dictionaries with two entries, like the base classes.