Closed t => ????
You want a closed type?
The parameter to a class is a type...
Actually if you allow undecidable instances you can use the generic
instance to close the class
class OnlyInt a
instance OnlyInt Int
instance Fail () => OnlyInt x
Where Fail is a class with no instances, that is not exported!
If you try and add an instance to OnlyInt the program will fail
with overlapping instances.
Keean.
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