That would be nice. It would also be nice to be able to use _ in type signatures as in: const :: a -> _ -> a const x _ = x During type checking each _ could be replaced by a new unique type variable. Visa versa should also be possible: during type inferencing each unique type variable could be replaced by a _. Bas On Jan 9, 2012 6:22 AM, "wren ng thornton" <wren@freegeek.org> wrote:
On 1/8/12 8:32 AM, Bas van Dijk wrote:
On 23 December 2011 17:44, Simon Peyton-Jones<simonpj@**microsoft.com<simonpj@microsoft.com>> wrote:
My attempt at forming a new understanding was driven by your example.
class Functor f where type C f :: * -> Constraint type C f = ()
sorry -- that was simply type incorrect. () does not have kind * -> Constraint
So am I correct that the `class Empty a; instance Empty a` trick is currently the only way to get default associated empty constraints?
Couldn't the following work?
class Functor f where type C f :: * -> Constraint type C f _ = ()
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, ~wren
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