On Thu, May 20, 2004 at 07:34:18PM +0100, MR K P SCHUPKE wrote: > that is not the case with "-fallow-undecidable-instances" ... as far as > I understand it , ghc never considers the dependancies when selecting an > instance. If you don't think so you will need to show me an example where > it clearly does... as I haven't seen one yet (but just because I haven't > seen it doesn't mean its not possible),,,
Am I to understand you're asserting that GHC "undecidable-instances" are in fact decidable? Hugs explicitly documents its type system as being undecidable, and I'd presumed this was the 'make GHC behave that way too' flag. > I mean, given two instances like: > > instance a b c > instance d e f > > there is no way to tell between them... if you said choose a in preferenc > 'a' would be chosen all the time. If you were to indicate one instance declaration was preferred, and both _could otherwise yield a suitable instance_, then that would be prefered. (Though if one were to 'search' in the preference order of the rules, one wouldn't need to find more than one in any event.) _______________________________________________ Glasgow-haskell-users mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
