Wolfgang Jeltsch wrote:

Am Montag, 3. Juli 2006 18:46 schrieb Simon Peyton-Jones:

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Thanks. Can you confirm that it's fixed in 6.4.2? And if so, can you record that too? No point in us haring after fixed bugs!

S

As Chris Kuklewicz pointed out, this bug doesn't seem to be completely fixed in 6.4.2. Currently, I neither can confirm this nor can I disprove it since at the moment there seem to be no Debian packages for 6.4.2 which I could install and I don't have the time to install GHC from source.

Best wishes, Wolfgang

I am using ghc-6.4.2 from darwinports on OS X 10.4.7 Can I help confirm / test this with something test cases? The older messages were:

Wolfgang Jeltsch wrote:

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Hello everybody,

I wanted to do something like that:

data Pair :: (* -> *) -> * where Pair :: a b -> b -> Pair a

data Sel :: * -> * where A :: Sel Bool B :: Sel Integer

showSnd :: Pair Sel -> String showSnd (Pair A bool) = show bool showSnd (Pair B integer) = show integer

However, GHC 6.4.1 with -fglasgow-exts complains in the second last and last line that there is no instance for (Show b). I don't really understand this since in my opinion it is clear that bool :: Bool and integer :: Integer and that therefore bool and integer are showable. What's the problem with my code?

Best wishes, Wolfgang

I cut and pasted your code into ghci-6.4.2 with -fglasgow-exts and there was no error. And I can (print (showSnd (Pair A True)) and (print (showSnd (Pair B 8))) but when I try to compile it with ghc-6.4.2 it complains about the Show instance. I find this deeply wierd, and it seems like a bug.

Changing the definition of Pair made it compile and run with ghc:

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data Pair :: (* -> *) -> * where Pair :: (Show b) => a b -> b -> Pair a