Thank you!
I imagine that if you think you've fixed it then you have, but here's
an example:
Prelude Data.Generics> (\x -> case cast x of Just x'@(a,b) -> print x'; Nothing
-> putStrLn "No match") (2::Int,3::Int)
Top level:
No instance for (Show (IO ()))
arising from use of `print' at Top level
Probable fix: add an instance declaration for (Show (IO ()))
In a 'do' expression: print it
I think the real error is that (,) is missing an instance...
Frederik
On Mon, May 23, 2005 at 09:33:49AM +0100, Simon Peyton-Jones wrote:
> Good point
>
> Happily, I improved this error message (which has been in SourceForge
> for some time) last Friday. At least I hope so; you didn't actually
> give an example. If you do, I'll try it. Or check out the HEAD and see
> if things have improved.
>
> Simon
>
> | -----Original Message-----
> | From: [EMAIL PROTECTED]
> [mailto:glasgow-haskell-bugs-
> | [EMAIL PROTECTED] On Behalf Of Frederik Eaton
> | Sent: 21 May 2005 14:34
> | To: glasgow-haskell-bugs@haskell.org
> | Subject: ghci obscurity
> |
> | Often ghci will give me the following message instead of something
> | helpful:
> |
> | Top level:
> | No instance for (Show (IO ()))
> | arising from use of `print' at Top level
> | Probable fix: add an instance declaration for (Show (IO ()))
> | In a 'do' expression: print it
> |
> | I don't know how hard it would be to fix, but it's kind of a nuisance.
> | It seems to only come up when something else is wrong, but it often
> | comes up *instead* of a good error message for the real problem,
> | making it very hard to track the real problem down.
> |
> | Frederik
> |
> | --
> | http://ofb.net/~frederik/
> | _______________________________________________
> | Glasgow-haskell-bugs mailing list
> | Glasgow-haskell-bugs@haskell.org
> | http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
>
--
http://ofb.net/~frederik/
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