GHC 6.6 Data.Tuple incompatibility

Bulat Ziganshin bulat.ziganshin at
Thu Oct 19 16:27:47 EDT 2006

Hello John,

Thursday, October 19, 2006, 11:21:37 PM, you wrote:

> I had this code that worked in GHC 6.4:

> type CommandHandler = FTPServer -> String -> IO Bool
> type Command = (String, (CommandHandler, (String, String)))

isnt' it better in such cases use the new datatype?

data Command = Command String CommandHandler String String

> After discussing it with Ian Lynagh, his conclusion was that the problem
> is that Data.Tuple was not compiled with overlapping instances support,
> and that it probably ought to be.  He asked me to post here to see if
> everyone else felt the same way.

the problem will arrive with any 'base' type constructor used in such
way - [], maybe, either

Best regards,
 Bulat                            mailto:Bulat.Ziganshin at

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