Re: Proposal: derive Typeable for Data.Monoid types

On 2014-05-27 at 10:42:30 +0200, Roman Cheplyaka wrote:

* Herbert Valerio Riedel [2014-05-27 10:36:46+0200]

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On 2014-05-27 at 08:31:14 +0200, Roman Cheplyaka wrote:

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I was surprised to find out that wrappers like Last do not have Typeable instances. Let's add them.

Fyi, Data.Monoid has been given a `{-# LANGUAGE AutoDeriveTypeable #-}` in

http://git.haskell.org/ghc.git/commitdiff/1d1ff77aaa09efaddc8cfe0dcf92d67632...

which should take care of not forgetting a 'deriving Typeable' in the future for any new entities defined in Data.Monoid.

Cool! I take it this is already solved in HEAD, then? Any reason not to enable AutoDeriveTypeable for the whole base (and other core packages)?

You can't enable it everywhere in base due to module-import cycles (you need to import Data.Typeable before you can AutoDeriveTypeable a module), but other than that, the plan is to enable it wherever possible in base. As for other core-packages, it would be sensible to use AutoDeriveTypeable only for packages which don't support GHC versions prior to GHC 7.8 (AutoDeriveTypeable was introduced with GHC 7.8.1).