lenses Questions
1
Lens is a function that perform immutable record modification: it copies the record modifying part of its content. Lenses is a library that allows you to combine lenses to attain more complicated m...
Threaten asked 16/1, 2016 at 1:2
2
Solved
Suppose I have a lens like at _ that needs some Maybe a:
import Data.Map as M
m = M.fromList [(1,(2,3))]
--set 2nd element
m ^. at 1 .~ Just (4,5)
--gives fromList [(1,(4,5))]
m ^. at 1 .~ Nothin...
Healing asked 13/1, 2016 at 5:4
2
Solved
If you browse through Lens entry on hackage, Lens Github's repo, or even google about Lens, you will find a lot of partial references such as introductory tutorials/videos, examples, overviews and ...
Sport asked 20/4, 2015 at 8:22
2
Solved
I am struggling to figure out an issue with manipulating JSON with Aeson lenses. My task is as simple as to add a key to a nested object in JSON. I was able to change the existing keyby means of:
...
Richma asked 29/12, 2015 at 12:33
1
Solved
I have a nested case classes structure in a List
for simplicity will use following as an example -
case class Address(street: String, city: String, state: String, zipCode: Int)
case class Perso...
Nguyen asked 9/11, 2015 at 15:31
3
Solved
Defined some nested case classes with List fields:
@Lenses("_") case class Version(version: Int, content: String)
@Lenses("_") case class Doc(path: String, versions: List[Version])
@Lenses("_") ca...
Bensky asked 28/10, 2015 at 11:35
3
I'm trying to perform a manipulation of a nested data structure containing lists of elements. After mucking around with various approaches I finally settled on lenses as the best way to go about do...
3
Solved
Some nested case classes and the field addresses is a Seq[Address]:
// ... means other fields
case class Street(name: String, ...)
case class Address(street: Street, ...)
case class Company(addres...
Monody asked 21/10, 2015 at 13:54
2
Why do we need Control.Lens.Reified? Is there some reason I can't place a Lens directly into a container? What does reify mean anyway?
1
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I am trying to read the documentation in Edward Kmett's Lens package. I am not familiar with a lot of the terms used (profunctor, isomorphism, monomorphic, contravariant, bifunctor, etc...)
What w...
Evictee asked 30/9, 2015 at 22:40
3
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While working on a state called AppState I want keep track of the number of, say, instances. These instances have distinct ids of type InstanceId.
Therefore my state look likes this
import Contro...
Gervais asked 2/9, 2015 at 12:34
3
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A "lens" and a "partial lens" seem rather similar in name and in concept. How do they differ? In what circumstances do I need to use one or the other?
Tagging Scala and Haskell, but I'd welcome ex...
1
I've been reading A wreq tutorial:
A lens provides a way to focus on a portion of a Haskell value. For
example, the Response type has a responseStatus lens, which
focuses on the status informa...
Devan asked 8/3, 2015 at 17:18
1
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Can anyone explain *what is lenses` in terms of OCaml?
I tried to google it, but almost all of them are in Haskell's world.
Just wish some simple demonstrations for it in OCaml's world, like wha...
1
Is there an equivalent of makeLenses for GADTs? If I have a simple GADT like:
data D a b where
D :: (Ord a, Ord b) => !a -> !b -> D a b
Is there a way to generate lenses automatically ...
2
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Is there a way for me to only export specific getters xor setters from a module with a lens?
For example, let's assume a data structure that has an invariant of being always >= 0, being modifi...
Cyprinid asked 14/12, 2014 at 23:9
1
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I have a function that produces an updated board from an input and a board, if the move is permitted by the rules of the game:
move :: Input -> Board -> Maybe Board
The board is wrapped in...
Gumwood asked 16/1, 2015 at 19:23
1
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I'm trying to refactor my function by giving it a lens argument (from the xml-lens package). I'm missing something about type quantifiers. What is going on here?
*Main> let z name = listToMaybe...
3
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I recently discovered the lens package on Hackage and have been trying to make use of it now in a small test project that might turn into a MUD/MUSH server one very distant day if I keep working on...
Geophysics asked 17/11, 2012 at 20:38
2
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I want to convert this line of code map (^?! ix 0) [[0, 1], [4, 5], [9, 1]] to entirely use lenses, so something like [[0, 1], [4, 5], [9, 1]] & each . ix 0. However, the types don't match up. ...
2
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The standard makeLenses implementation generates lenses for all the fields of a record which begin with underscore. I very much dislike the idea of having to introduce such an awkward naming conven...
Arber asked 16/6, 2013 at 10:49
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While immutability praised by many, I found it hard to maintain in mainstream programming. In my experience, programmers sooner than later will make fields mutable again to avoid refactoring large ...
Mensa asked 24/8, 2013 at 23:3
1
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Based on:
import shapeless._
case class Content(field: Int)
lens[Content] >> 'field
I am trying to make a lens-creating method, something along:
def makeLens[T <: Product](s: Symbol) ...
1
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Does the identity function in Clojure have the same usage and purpose as the id function in Haskell?
In Clojure we have the identity function. It is used as follows:
user=> (filter identity [1 2 3 nil 4 false true 1234])
(1 2 3 4 true 1234)
user=> (partition-by identity (sort "abcdaabccc")...
3
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I am trying to learn about lenses by implementing it in Haskell. I have implemented the view combinator as follows:
{-# LANGUAGE RankNTypes #-}
import Control.Applicative
import Data.Traversable
...
Soneson asked 10/9, 2014 at 19:22
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