I seem to recall Matt Morrow having some code lying around for automatically generating such instances using haskell-src-exts. I wonder how hard it would be to adapt to Template Haskell. -Edward Kmett
On Tue, Apr 14, 2009 at 2:03 AM, Ryan Ingram <ryani.s...@gmail.com> wrote: > You might be able to write some Template Haskell to derive the Show > instance. > > It's a bit tricky, because there are some types which can't have Show > derived, such as: > > data Foo where > Broken :: a -> Foo > > What should > show (Broken id) > do? > > -- ryan > > On Mon, Apr 13, 2009 at 9:28 PM, Norman Ramsey <n...@cs.tufts.edu> wrote: > > 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 > > _______________________________________________ > > Haskell mailing list > > Haskell@haskell.org > > http://www.haskell.org/mailman/listinfo/haskell > > > _______________________________________________ > Haskell mailing list > Haskell@haskell.org > http://www.haskell.org/mailman/listinfo/haskell >
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