On Tue, May 19, 2009 at 6:22 PM, Denis Bueno wrote:

On Tue, May 19, 2009 at 16:07, Jason Dusek 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.htm...

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 _______________________________________________

I think what he's referring to is that StandaloneDeriving actually has the syntax deriving instance Eq Foo not deriving Eq for foo Alex

2009/05/20 Simon Peyton-Jones :

| I'm a little puzzled by these seeming duplicate pages in the | manual: | |   http://www.haskell.org/ghc/dist/current/docs/users_guide/type-extensions.htm... | |   http://www.haskell.org/ghc/dist/current/docs/users_guide/data-type-extension...

The former is garbage. It's part of an *earlier* iteration of the HEAD user manual, left around by mistake.

| They give slightly different section numbers to similar stuff. | 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.htm...

Same problem. Standalone deriving is described here...

I found it linked from the wiki page on stand-alone deriving (which also happens to have the offending sytnax). -- Jason Dusek |...the wiki page on stand-alone deriving...| http://haskell.org/haskellwiki/?title=GHC/Stand-alone_deriving_declarations&action=history

Yes, it is fixed (the link is to the history). -- Jason Dusek