https://github.com/monadplus/scala-lenses
Diving into Optics through https://github.com/julien-truffaut/Monocle.
https://github.com/monadplus/scala-lenses
Last synced: about 1 month ago
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Diving into Optics through https://github.com/julien-truffaut/Monocle.
- Host: GitHub
- URL: https://github.com/monadplus/scala-lenses
- Owner: monadplus
- License: mit
- Created: 2019-04-22T14:10:10.000Z (about 7 years ago)
- Default Branch: master
- Last Pushed: 2022-02-12T02:14:09.000Z (over 4 years ago)
- Last Synced: 2025-10-29T17:56:38.734Z (8 months ago)
- Language: JavaScript
- Homepage:
- Size: 5.13 MB
- Stars: 4
- Watchers: 0
- Forks: 0
- Open Issues: 10
-
Metadata Files:
- Readme: README.md
- License: LICENSE
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README
# The magic of composition
During this talk, we are going to dive into _Monocle_ and
unravel the mystery surrounding __optics__.
Slides [here](https://monadplus.github.io/scala-lenses/).
## Public
This talk is aimed for developers with basic notion of:
- Scala
- Functional programming
The examples are in written in Scala so a basic notion of the syntax is assumed.
If you are not acquainted with the words `Functor, Appicative, Foldable, Traverse`
I would recommend visiting first the [cats](https://typelevel.org/cats/typeclasses.html)
and [typeclassopedia](https://wiki.haskell.org/Typeclassopedia) and get a basic notion of these concepts.
## Motivation
```scala
case class Street(number: Int, name: String)
case class Address(city: String, street: Street)
case class Company(name: String, address: Address)
case class Employee(name: String, company: Company)
val employee = Employee("john", Company("awesome inc", Address("london", Street(23, "high street"))))
```
Old plain scala:
```scala
employee.copy(
company = employee.company.copy(
address = employee.company.address.copy(
street = employee.company.address.street.copy(
name = employee.company.address.street.name.capitalize // luckily capitalize exists
)
)
)
)
```
With lenses:
```scala
(company composeLens
address composeLens
street composeLens streetName).modify(_.capitalize)(employee)
```
## Libraries
Lenses provides __more composable__ versions of the abstractions you already known how to use in Scala/Haskell.
- [monocle](https://github.com/julien-truffaut/Monocle) (scala)
- [lenses](https://github.com/ekmett/lens#lens-lenses-folds-and-traversals) (haskell)
Both libraries provides rich APIs to work with lenses and a battery of utilities to make your life easier.
Lenses is based on Van Laarhoven optics while Monocle uses an alternative encoding. The reason behind not using
Van Laarhoven nor profunctor optics is because they are inefficient in scala and not well supported by the language
(scala does not support N-rank types).
## Hierarchy
_Monocle lenses hierarchy_
_Lenses hierarchy in haskell_
## Composition
The result is their lowest upper bound in the hierarchy (or an error if that bound doesn't exist).
| | Getter | Iso | Lens | Optional | Prism | Setter | Traversal |
| ------------- |:----------:|:----------:|:----------:|:------------:|:----------:|:----------:|:-------------:|
| **Getter** | **Getter** | Getter | Getter | Fold | Fold | - | Fold |
| **Iso** | Getter | **Iso** | Lens | Optional | Prism | Setter | Traversal |
| **Lens** | Getter | Lens | **Lens** | Optional | Optional | Setter | Traversal |
| **Optional** | Fold | Optional | Optional | **Optional** | Optional | Setter | Traversal |
| **Prism** | Fold | Prism | Optional | Optional | **Prism** | Setter | Traversal |
| **Setter** | - | Setter | Setter | Setter | Setter | **Setter** | Setter |
| **Traversal** | Fold | Traversal | Traversal | Traversal | Traversal | Setter | **Traversal** |
## Credits:
- https://github.com/julien-truffaut/Monocle (J. Truffaut et al)
- https://hackage.haskell.org/package/lens (E. Kmett)