Generalized newtype deriving 6.6 vs. 6.8
isaacdupree at charter.net
Mon Nov 5 10:38:11 EST 2007
Simon Peyton-Jones wrote:
> Well it's debatable. Suppose we have
> newtype Foo = MkFoo String deriving( Num )
> Do you want to generate
> instance Num String => Num Foo
Personally, I think I would like that -- along with a warning message.
It makes it clearer to me that I can do
newtype Foo a = MkFoo a deriving( Num )
without requiring that Foo can only be instantiated with types in Num.
I'm not sure though.
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