#3954: Contexts on empty data decls falsely rejected
---------------------------------+------------------------------------------
Reporter: ksf | Owner:
Type: bug | Status: new
Priority: normal | Component: Compiler (Type checker)
Version: 6.12.1 | Keywords:
Os: Unknown/Multiple | Testcase:
Architecture: Unknown/Multiple | Failure: GHC rejects valid program
---------------------------------+------------------------------------------
HList uses EmptyDataDecls and contains
{{{
data HNat x => Label x ns desc
}}}
which fails with
{{{
Data/HList/Label3.hs:37:0:
No context is allowed on a GADT-style data declaration
(You can put a context on each contructor, though.)
}}}
, regressing from 6.10.
My crystal ball tells me someone has been simplifying the implementation
of EmptyDataDecls to be GADTs without {{{where}}}, and missed the corner
case.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3954>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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