[Haskell] deriving Show for GADT?
lennart at augustsson.net
Tue Apr 14 04:27:55 EDT 2009
If it's easy I think just generating the code and let the type checker
report any problems would be a great thing for standalone deriving.
On Tue, Apr 14, 2009 at 10:10 AM, Simon Peyton-Jones
<simonpj at microsoft.com> wrote:
> Yes, indeed, see http://hackage.haskell.org/trac/ghc/ticket/3012
> Incidentally, the main Haskell list isn't the right place for GHC-specific questions. glasgow-haskell-users at haskell.org is the place
> | -----Original Message-----
> | From: haskell-bounces at haskell.org [mailto:haskell-bounces at haskell.org] On Behalf Of
> | Norman Ramsey
> | Sent: 14 April 2009 05:28
> | To: haskell at haskell.org
> | Subject: [Haskell] deriving Show for GADT?
> | I've got a fairly large GADT for which I wished to use
> | deriving (Show)
> | but I got a mysterious error message:
> | Exp.hs:13:11:
> | Can't make a derived instance of `Show (Exp a)'
> | (`Exp' has non-Haskell-98 constructor(s))
> | In the data type declaration for `Exp'
> | This is from GHC. Does anybody know a compiler option or other trick
> | that will coax the compiler into producing a Show instance.
> | (I know I can write one by hand, but I'd rather not bother.)
> | Norman
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