I have the following class and instance
class Register a r | a -> r where
instance (Register a ra, Register b rb) =>
Register (a,b) (ra,rb) where
and GHC refuses the instance because of violated Coverage Condition.
I have more instances like
instance Register Int8 (Reg Int8) where
instance Register Word8 (Reg Word8) where
and for the set of instances I plan, the instance resolution will always
terminate. I remember that the term 'undecidable instance' is not fixed
and may be relaxed if a more liberal condition can be found. Is there a
place, say a Wiki page, where we can collect examples where we think that
the current check of GHC is too restrictive?
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