baffling manual sections

[Denis Bueno]

On Tue, May 19, 2009 at 16:07, Jason Dusek <jason.dusek at gmail.com> wrote:
>  The former page also has a curious discussion of standalone
>  deriving with a `for` keyword:
>
>    http://www.haskell.org/ghc/dist/current/docs/users_guide/type-extensions.html#stand-alone-deriving

Without this extension, adding an Eq implementation to a data type for
which you do not have source requires an explicit class declaration,
even if there is no reason the original data type author couldn't have
written "deriving Eq".  Standalone deriving allows you to get the
convenience of deriving classes everywhere, not just on datatypes for
which you can obtain, and use, the source.

                              Denis