[GHC] #2436: Bad warning when exporting data families

[Manuel M T Chakravarty]

David Waern:
> 2008/7/13 GHC <trac at galois.com>:
>> #2436: Bad warning when exporting data families
>> ------------------------- 
>> +--------------------------------------------------
>>   Reporter:  rl        |        Owner:  chak
>>       Type:  bug       |       Status:  new
>>   Priority:  normal    |    Milestone:
>>  Component:  Compiler  |      Version:  6.9
>>   Severity:  normal    |   Resolution:
>>   Keywords:            |     Testcase:
>> Architecture:  Unknown   |           Os:  Unknown
>> ------------------------- 
>> +--------------------------------------------------
>> Changes (by chak):
>>
>> * owner:  => chak
>>
>> --
>> Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2436#comment:1 
>> >
>>
> Correct me if I'm wrong, but shouldn't GHC report here that data
> instances can't be exported? Or can they be exported? When
> implementing Type Family support in Haddock, I could see no way to
> export type/data instances using the GHC AST.

They cannot be explicitly exported - they are really like class  
instances wrt to import/export.

However, you *can* export the data constructors introduced by a data  
instances (just like you can export the data constructors of vanilla  
algebraic data types).  That's what rl is doing here.  He is exporting  
the data constructor, not the instances (which is implicitly exported  
anyway).

Manuel