Linear lens combinators #195
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| instance (Functor f, Functor g) => Functor (Compose f g) where | ||
| fmap f (Compose x) = Compose (fmap (fmap f) x) | ||
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| instance (Applicative f, Applicative g) => Applicative (Compose f g) where | ||
| pure x = Compose (pure (pure x)) | ||
| (Compose f) <*> (Compose x) = Compose (liftA2 (<*>) f x) | ||
| liftA2 f (Compose x) (Compose y) = Compose (liftA2 (liftA2 f) x y) | ||
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I like these. I needed them for linear-streams.
| @@ -67,6 +70,10 @@ assoc = iso Bifunctor.lassoc Bifunctor.rassoc | |||
| (.>) :: Optic_ arr a b s t -> Optic_ arr x y a b -> Optic_ arr x y s t | |||
| Optical f .> Optical g = Optical (f P.. g) | |||
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| lens :: (s #-> (a, b #-> t)) -> Lens a b s t | |||
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Very nice; me likey 😏
| @@ -139,3 +152,10 @@ withIso (Optical l) f = f fro to | |||
| withPrism :: Optic_ (Market a b) a b s t -> ((b #-> t) -> (s #-> Either t a) -> r) -> r | |||
| withPrism (Optical l) f = f b m | |||
| where Market b m = l (Market id Right) | |||
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| withLens :: Optic_ (Linear.Kleisli (Compose ((,) a) (FUN 'One b))) a b s t -> s #-> (a, b #-> t) | |||
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Given that this is just migration and that I'm going to take a pass through optics, this, although complicated, is fine right now. When I take a pass I'm going to comment that withLens is (kind of) the dual of lens and the (Optic_ ...) is basically (a #-> (a, b -> b)) -> (s #-> (s, t -> t)).
One question: could we change FUN 'One b to (->) b which is much more readable to me?
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withLensis (kind of) the dual oflens
The better term is inverse
could we change
FUN 'One b to (->) bwhich is much more readable to me?
It would not work. (->) is FUN 'Many. There are many ways to make this simpler, but I don't think that they are much needed. The type after Optic_ is not meant to be read. See the lens library for how to document such primitives.
It's a weird issue. I had it once before (on #189), I think there's a cache invalidation issue somewhere. Previously I got around that by randomly changing a parameter name on one of the upstream modules. Totally unsatisfactory "solution", I know. |
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I can reproduce the stack failure locally. With a clean Stack version I don't really have time to figure this out, right now, though. |
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Okay, I'll play with parameter names and then merge. |
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It does make me very sad, if that's the solution we end up settling on. |
I agree. I spent some time trying to solve it but to no avail. So I gave up and opened #199, it's still not a solution; but should be better than having to change random stuff. |
With a linear lens, we cannot linearly set the value at the lens site in general, however, we can swap the value at the lens site for another, which we get out of the operation. Ported from #79.
Translation between the profunctor definition of lens and the more straightforward getter/setter pair. Ported from #79.
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A handful of utilities for linear lens.
These are ported from #79 .