ConstraintKinds and default associated empty constraints
aslatter at gmail.com
Mon Jan 9 07:30:41 CET 2012
On Sun, Jan 8, 2012 at 11:21 PM, wren ng thornton <wren at freegeek.org> wrote:
> Couldn't the following work?
> class Functor f where
> type C f :: * -> Constraint
> type C f _ = ()
I get a parse error from that.
class Functor f where
type FC f :: * -> Constraint
type FC f a = ()
gives the error:
Number of parameters must match family declaration; expected 1
In the type synonym instance default declaration for `FC'
In the class declaration for `Functor'
> It seems to me that adding const to the type level (either implicitly or
> explicitly) is cleaner and simpler than overloading () to be Constraint,
> *->Constraint, *->*->Constraint,...
> Live well,
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