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

[GHC-2]

#2436: Bad warning when exporting data families
------------------------+---------------------------------------------------
    Reporter:  rl       |       Owner:          
        Type:  bug      |      Status:  new    
    Priority:  normal   |   Component:  Compiler
     Version:  6.9      |    Severity:  normal  
    Keywords:           |    Testcase:          
Architecture:  Unknown  |          Os:  Unknown
------------------------+---------------------------------------------------
 {{{
 module Foo ( T ) where
 data family T a
 }}}

 {{{
 module Bar ( T(..), module Foo ) where
 import Foo
 data instance T Int = TInt
 }}}

 GHC issues the following warning:

 {{{
 Bar.hs:1:20: Warning: `T' is exported by `module Foo' and `T(..)'
 }}}

 However, that's the only way to export both module Foo and TInt from Bar.
 I don't think GHC should warn here.

--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2436>
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[GHC-2]

#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>
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[David Waern-2]

2008/7/13 GHC <trac@...>:

> #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>
> GHC <http://www.haskell.org/ghc/>
> The Glasgow Haskell Compiler
> _______________________________________________
> Glasgow-haskell-bugs mailing list
> Glasgow-haskell-bugs@...
> http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
>
>

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.

David
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[David Waern-2]

2008/7/13 David Waern <david.waern@...>:

> 2008/7/13 GHC <trac@...>:
>> #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>
>> GHC <http://www.haskell.org/ghc/>
>> The Glasgow Haskell Compiler
>> _______________________________________________
>> Glasgow-haskell-bugs mailing list
>> Glasgow-haskell-bugs@...
>> http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
>>
>>
>
> 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.
>
> David
>

With exported, I mean explicitly exported, of course.

David
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[Manuel M T Chakravarty]

David Waern:

> 2008/7/13 GHC <trac@...>:
>> #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

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[David Waern-2]

2008/7/15 Manuel M T Chakravarty <chak@...>:
> 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).

Ah, I see. So if you have multiple instances, the union of all their
data constructors will be exported? What happens in the case of
associated types? Are their data constructors always exported, or can
they also be exported explicitly somehow?

David
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[David Waern-2]

2008/7/15 David Waern <david.waern@...>:

> 2008/7/15 Manuel M T Chakravarty <chak@...>:
>> 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).
>
> Ah, I see. So if you have multiple instances, the union of all their
> data constructors will be exported? What happens in the case of
> associated types? Are their data constructors always exported, or can
> they also be exported explicitly somehow?

Sorry for bothering you, I just realized all of this is explained on
the wiki page.

David
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[GHC-2]

#2436: Bad warning when exporting data families
----------------------+-----------------------------------------------------
 Reporter:  rl        |          Owner:  chak  
     Type:  bug       |         Status:  new    
 Priority:  normal    |      Milestone:  6.10.1
Component:  Compiler  |        Version:  6.9    
 Severity:  normal    |     Resolution:        
 Keywords:            |     Difficulty:  Unknown
 Testcase:            |   Architecture:  Unknown
       Os:  Unknown   |  
----------------------+-----------------------------------------------------
Changes (by igloo):

  * difficulty:  => Unknown
  * milestone:  => 6.10.1

--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2436#comment:2>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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