[Haskell-cafe] What's the difference?

[PR Stanley]

>>What is the difference between
>>
>>     data T0 f a = MkT0 a
>>     instance Eq (T0 f a) where ...
>>
>>         and
>>
>>     data T0 f a = MkT0 a
>>     instance Eq a => Eq (T0 f a) where ...
>The second one says that "TO f a" is only an instance of "Eq" if "a" 
>is, while the first says that "TO f a" is an instance regardless of 
>the type of its arguments.
>
More explanation please. :-)

Much obliged, Paul