[GHC] #8132: Warning for Typeable instances misplaced

[GHC]

#8132: Warning for Typeable instances misplaced
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        Reporter:  scottgw                       |            Owner:
            Type:  bug                           |  dreixel
        Priority:  normal                        |           Status:  new
       Component:  Compiler                      |        Milestone:
      Resolution:                                |          Version:  7.7
Operating System:  Unknown/Multiple              |         Keywords:
 Type of failure:  Incorrect warning at          |     Architecture:
  compile-time                                   |  Unknown/Multiple
       Test Case:                                |       Difficulty:
        Blocking:                                |  Unknown
                                                 |       Blocked By:
                                                 |  Related Tickets:
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Comment (by simonpj):

 Yurgh. You are quite right.  It's really hard to move on ''and'' maintain
 backwards compatibility!

 I'm open to advice.  Two alternatives make sense to me:

  * Maintain total backward compat for a single release, by putting the new
 stuff in `Data.NewTypeable` for one release (with heavy deprecation
 messages), and ''then'' in 7.10 moving it to `Data.Typeable`, while making
 the old `Data.Typeable` into `Data.OldTypeable`.

  * Just make the breaking change now (which as you point out, we have
 already done in HEAD).  In that case we should make manual `Typeable`
 instances an error right away.

 I'd prefer the latter.  In practice each release of GHC does typically
 require some changes wrt base, and I doubt that 7.8 will be an exception
 to that.  But I'm sensitive to what users want.

 Simon

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8132#comment:7>
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