Disjoint type classes
Marcin 'Qrczak' Kowalczyk
5 Mar 2001 21:12:30 GMT
Thu, 18 Feb 1988 08:17:58 +0100, Jose Emilio Labra Gayo <email@example.com> pisze:
> Which doesn't work because Haskell doesn't detect that
> "Integral" and "Fractional" are disjoint.
And indeed there is no disjointness concept in the language.
Nothing prevents from making a type an instance of both.
> Is there a way to implement these type classes with current Haskell
I'm afraid not. In the standard way you must decide for each type
separately. At most you could use ghc with -fallow-overlapping-instances
-fallow-undecidable-instances, which would allow to define one of your
instances - the other would have to be defined for each type separately;
but these options are not nice.
__("< Marcin Kowalczyk * firstname.lastname@example.org http://qrczak.ids.net.pl/
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