Neil Mitchell wrote:
The trouble, of course, is that classes could have rather complicated
"minimum instance" requirements. Still, if someone came up with a
decent syntax such as (but better than)
You don't need a syntax, the information is already there. You also
don't need to do complicated non-termination analysis. Taking the
slightly simpler example of:
class Eq a where
a == b = not (a /= b)
a /= b = not (a == b)
From this example its clear that (==) depends on (/=) and that (/=)
depends on (==). i.e. its obvious they form a cycle.
Ah, but it's not "clear" at all :) How about something wicked like
class UselessEq a where
(==), (/=) :: Bool -> a -> Bool
True == b = b
a == b = not (a /= b)
False /= b = b
a /= b = not (a == b)
This may be useless but I wouldn't be surprised if interesting examples
utilizing polymorphic recursion or multi parameter type classes exist.
Regards,
apfelmus
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