Eq1, Ord1, Show1: move from eq1, compare1, showsPrec1 to liftEq, liftCompare, liftShowsPrec
lemming at henning-thielemann.de
Mon Jan 11 19:20:46 UTC 2016
me again ...
On Mon, 11 Jan 2016, Ryan Scott wrote:
> You're talking about this transformers issue , correct?
> Not only that, but there are a couple of datatypes in transformers that
> already resolve their Eq instances in an identical way to how Apply
> would (for instance, IdentityT, which is isomorphic to Apply ).
One of my applications is to use functor things in a Set, which requires
Ord constraint. With IdentityT I can write:
class Ord1 f => Elem f where
method :: ...
transform :: (Elem f, Ord a) => Set (IdentityT f a) -> Set (IdentityT f a)
Without IdentityT I would have constraint (Ord (f a)).
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