#7481: Partially promoted data types
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Reporter: simonpj | Owner:
Type: bug | Status: new
Priority: high | Milestone: 7.8.1
Component: Compiler | Version: 7.6.1
Keywords: | Os: Unknown/Multiple
Architecture: Unknown/Multiple | Failure: None/Unknown
Difficulty: Unknown | Testcase:
Blockedby: | Blocking:
Related: |
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Description changed by simonpj:
Old description:
> Consider
> {{{
> data D a where
> D1 :: a -> D a
> D2 :: (a~Int) => D a
> D3 :: forall (a:k). Proxy a -> D b
>
> }}}
> Is `D` a promoted type?
>
> Well, `D1` is promotable, but `D2` is not because of constraints in its
> type, and neither is `D3` because it uses kind polymorphism. It's a bit
> odd to promote only one of the three constructors, but that is what
> happens right now.
>
> We should probably check for promotability of all data constructors, and
> promote all or none. A bit of fiddling around is need to do this, so I'm
> opening a ticket. It's not terribly pressing.
New description:
Consider
{{{
{-# LANGUAGE DataKinds, PolyKinds #-}
data D a where
D1 :: a -> D a
D2 :: (a~Int) => D a
D3 :: forall (a:k). Proxy a -> D b
}}}
Is `D` a promoted type?
Well, `D1` is promotable, but `D2` is not because of constraints in its
type, and neither is `D3` because it uses kind polymorphism. It's a bit
odd to promote only one of the three constructors, but that is what
happens right now.
We should probably check for promotability of all data constructors, and
promote all or none. A bit of fiddling around is need to do this, so I'm
opening a ticket. It's not terribly pressing.
--
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7481#comment:1>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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