#3702: deriving for GADTs
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Reporter: rwbarton | Owner:
Type: feature request | Status: new
Priority: normal | Component: Documentation
Version: 6.12.1 RC1 | Keywords:
Os: Unknown/Multiple | Testcase:
Architecture: Unknown/Multiple | Failure: None/Unknown
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I'm pleased to see that GHC 6.12.1 will include deriving for GADTs.
However, I discovered this in a quite accidental way. I tried appending
`deriving (Eq, Show)` to the end of my type declaration, without success,
and decided to check whether there was a request in Trac for the feature,
when I discovered ticket #3012. Sure enough, switching to a standalone
deriving clause worked when I compiled my program in GHC 6.12.1 RC1.
It would be nice if this feature were more easily discoverable. I think
it deserves mention in the release notes. Also, it would be great if the
error message for the non-standalone deriving clause (Can't make a derived
instance of ... / Constructor ... does not have a Haskell-98 type)
suggested the standalone syntax.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3702>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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