Well, this is not so general. It seems to be associated to the inferred contexts in automatically derived instances (generated with the "deriving" keyword). I will write a clear example as soon as I make sure what is different between GHC 6 and 7 about this.
2011/4/18 Alberto G. Corona <[email protected]> > By my little experience with GHC 7.* it seems that this version is > more "deterministic" when deriving instances. For example > if there is a general instance declaration such is: > > instance C1 x=> C2 x where .... > > then the absence of the C1 instance becomes an error. C1 instance > becomes a prerequisite for any C2 instance, where in previous > versions, that was just a overlapping instance in collision with any > other less general instance of the C2 class, so it could be overcomed > with the "OverlappingInstances" flag. > > Given that is not possible to hide instances, this is annoying. I´m > not saying that this is wrong or even If this is so, because this > could be a misinterpretation on my side based on the tests I have > done. Where can I read about the rationale of this change?. General > Instance derivations rules, as any rule system seem to me naturally > flexible and with different degrees of generalization rather tan > rigid. >
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