lenses | small functional lens library for TypeScript with the goal | Serialization library
kandi X-RAY | lenses Summary
kandi X-RAY | lenses Summary
@atomic-object/lenses is a small functional lens library for TypeScript with the goal of being small, with zero dependencies, and strong, precise types. It is inspired by Aether, for F#. Lenses are getter/setter pairs that let you represent a location within some data structure for both reading and updating that location. "Update" in this case is in the functional sense – not by mutation, but by creating a new data structure with a new value in the location of interest. A little like a pointer offset in C, but memory-, type-, and mutation-safe.
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Currently covering the most popular Java, JavaScript and Python libraries. See a Sample of lenses
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Trending Discussions on lenses
QUESTION
I wrote a function to query currency exchanges rate from an API. It works fine, but the code is way too long and unreadable. I thought someone would be able to help me simplify this, especially because there are many repeated patterns and operators like the repeated use of
EDIT: I didn't realize that binding anything to pure
is absolutely useless!
ANSWER
Answered 2022-Apr-10 at 18:00Wow, that is too long. Let's take it step by step; by the end, we will arrive at the following code snippet which I find much more natural to read but which performs exactly the same computation:
QUESTION
I am building an android application that lists down all camera devices, I want to list down all the camera devices and allow the user to use them all and not only that, I want also to allow the user to change the play with the resolution as they want, so I follow this link: https://developer.android.com/training/camera2/camera-enumeration
It recommends only using the camera devices with the flag:
...ANSWER
Answered 2022-Mar-30 at 00:06BACKWARD_COMPATIBLE devices are ones that support YUV and JPEG output and a bunch of basic camera behavior.
In general, only very few camera types won't list BACKWARD_COMPATIBLE; one such example is a pure depth camera, which won't produce JPEGs. For such devices, you have to manually check what output formats are actually supported via 'getOutputFormats', since it's likely something like JPEG won't be listed, or it may only support monochrome output and not color, which may make it impossible to use it with a video recorder.
If you're seeing a lot of devices get filtered out by excluding BACKWARD_COMPATIBLE, it'd be interesting to know, since in my experience they're very rare.
QUESTION
I am filling a form about joining a student team. There are some questions about computer vision. I had a little experience before hand, and i spent two days already researching the basics about depth estimation. I have the following question about the implementation of depth estimation.
Lets say i have a moving vehicle, and i am using cameras to estimate depth of various objects. Knowing the fundamental matrix, depth estimation boils down to solving a 3x3 linear system for each point in space. (Assuming there are no uncertainties with the pixel coordinates, or distortion from lenses).
The fundamental matrix itself is calculated using corresponding points from the 2 images. The question is, do i have to calculate the fundamental matrix at every moment (every iteration)? Do i calibrate the cameras at the initial setup and after that, the fundamental matrix is considered known?
...ANSWER
Answered 2022-Mar-14 at 23:41Once you calibrate your system, if extrinsic (relative position) and intrinsic (camera lenses, focal length, image resolution) parameters remain the same, then you don't need to recalculate the fundamental matrix F. You do it only once, and may store it for future use.
This is exactly what I do in my library, where you can find also an example where the fundamental matrix is calculated and used to draw epipolar lines.
I hope this answers your question.
Cheers
QUESTION
I write SplitMirror filter like in Apple Motion app or Snapchat lenses by using UIGraphics
to use it with real time camera feed or video processing, with single image request it works well like in attached image in the question but for multiple filtering request not. I think it's code must be changed from UIGraphics
to Core Image & CIContext
for better performance and less memory usage like CIFilters
and actually I don't know how to do it.
I tried several ways to convert it but I stuck on merging left and right, this can be done with `CICategoryCompositeOperations filters but which one is fit this case I o have idea, so need some help with this issue.
Filter code using UIGraphics
:
ANSWER
Answered 2022-Mar-02 at 08:02I think you are on the right track.
You can create the left half from the right half by applying transformations to it using let leftHalf = rightHalf.transformed(by: transformation)
. The transformation should mirror it and translate it to the correct position, i.e., next to the right half.
You can them combine the two into one image using let result = leftHalf.composited(over: rightHalf)
and render that result using a CIContext
.
QUESTION
I am trying to access a nested record using lenses and prisms in Haskell:
...ANSWER
Answered 2022-Mar-01 at 21:09Updated: As per comments, I've fixed some errors and added a few asides in [[double square brackets]].
Here's how/why your first mMistake
works...
A prism is an optic that focus on a "part" that may or may not be present in the "whole". [[Technically, it focuses on the sort of part that can be used to reconstruct an entire whole, so it really pertains to a whole that can come in several alternative forms (as in the case of a sum type), with the "part" being one of those alternative forms. However, if you're only using a prism for viewing and not setting, this added functionality isn't too important.]]
In your example, both _StateRun
and _Just
are prisms. The _Just
prism focuses on the a
part of a Maybe a
whole. Such an a
may or may not be present. If the Maybe a
value is Just x
for some x :: a
, the part a
is present and has value x
, and that's what _Just
focuses on. If the Maybe a
value is Nothing
, then the part a
is not present, and _Just
doesn't focus on anything.
It's somewhat similar for your prism _StateRun
. If the whole StateStep
is a StateRun x y
value, then _StateRun
focuses on that "part", represented as a tuple of the fields of the StateRun
constructor, namely (x, y) :: (Int, Maybe Text)
. On the other hand, if the whole StateStep
is a StatePause
, that part isn't present, and the prism doesn't focus on anything.
When you compose prisms, like _StateRun
and _Just
, and lenses, like stStep
and _2
, you create a new optic that combines the composed series of focusing operations.
[[As was pointed out in the comments, this new optic isn't a prism; it's "only" traversal. In fact, it's a specific kind of traversal, called an "affine traversal". A run-of-the-mill traversal can focus on zero or more parts, while an affine traversal focuses on exactly zero (part not present) or one (unique part present). The lens
library doesn't make the distinction between affine traversals and other sorts of traversals, though. The reason the new optic is "only" an affine traversal instead of a prism relates to that earlier technical point. Once you add lenses, you remove your ability to reconstruct the entire "whole" from a single "part". Again, if you're only using the optics for viewing, not setting, it won't really matter.]]
Anyway, consider the optic (affine traversal):
QUESTION
First time using lens
. set
and over
went easy enough and I thought it would be simple with view
: Use the same scheme to reference the inner part, but don't supply a new value or function. But Noooo. tst3 below gives the error below the code
. Anyone know what's going on?
ANSWER
Answered 2022-Feb-20 at 23:35ix 0
doesn't produce a lens, but a traversal.1
Informally, a lens is a "path" that will definitively reach a single value (if you follow it within a hypothetical larger value). A traversal is a path to zero or more values. You can set
or view
the single target of a lens. And you can set
the zero or more targets of a traversal (this simply updates all of them that are present, which is a no-op if there are zero present). But view
ing the targets of a traversal is less straightforward.
If view
simply took a traversal, and an outer structure, and gave you the target value, then it would have a problem. If there are multiple targets, how should it decide which to return? And if there are zero targets, it can't return anything; it would have to be partial. What it needs is a way of condensing zero-or-more values into a single value, so it can return that. And the Monoid
class provides exactly the facilities to do that; mempty
for if there aren't any targets at all, and <>
to condense multiple values to a single one. So view
with a traversal2 actually requires a Monoid
constraint on the returned type, and that's why you're getting the complaint about No instance for (Monoid Int) arising from a use of `ix'
.
And in case it isn't clear, you can often compose (with .
) different types of optics (the general term for "lens-ish things", including lenses, traversals, and several others). But the result has the capabilities of the least capable of the two inputs. So even though your inner
and w
are full lenses, composing them with a traversal produced by ix
results in a traversal, not a lens.
But in this case you know that you're using ix
. The specific kind of traversals ix
makes end up having zero or one target, rather than the zero or more targets that traversals have in general. So you could use preview
instead of view
; for a traversal it will produce a Maybe
containing Just
the first target of the traversal, or Nothing
if there weren't any. A Maybe
is exactly what the type system deems appropriate here, since ix
can't guarantee there will be a target value, but there won't be more than one.
In my experience, when I try to view
something and get this Monoid
instance error, it almost always means I have an optic that can't guarantee a result and I should actually be using preview
to get a Maybe
.
Simple example:
QUESTION
ANSWER
Answered 2022-Feb-01 at 19:22Completely removing the other options is currently not available. However, you can lock them as shown in the picture.
- Remove databricks-sql-access entitlement from default users group.
- Create a new group called 'sql-users-only' and give them only this entitlement. (so they won't see workspace and they can't spin up endpoints)
Resources: Databricks provide a lot of control using ACLs. Access control overview You can restrict the dashboard viewing options as well. Dashboard permissions
QUESTION
I am learning FP and I am trying to figure out how to handle events in react. For example, let's use following scenario:
...ANSWER
Answered 2021-Dec-12 at 10:45Add the type Todo
to the lensProp
call. You can also move it out of the component, because you don't need to generate the function whenever the component re-renders:
QUESTION
I am using Room in my Android App (Java) and there I have two entities with a 1:many relation.
Lens entity One lens can have multiple wears.
...ANSWER
Answered 2021-Dec-08 at 19:43The parent column needs to be the column that forms the relationship between the two. That is it should be the fk_lensId
column.
So :-
QUESTION
I have a JSON object that looks like this:
...ANSWER
Answered 2021-Dec-07 at 12:57It seems like because the JSON object is not an array of objects, the deserializer cannot convert it to an IEnumerable
Yes, it is not an array of objects, it is an object with others objects in it, I believe that using default serializers/deserializers you will not be able to work this JSON out.
Unless you end up using dynamic objects (can be a JObject) and then cast it to another structure, the only way is to write a custom serializer for this specific case and build an workaround this JSON.
You can try this:
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