Simple exemple with Lense & Optional & Transversal ?

[Ronan Michaux]

Hello,

I'm trying to learn Monocle, so I modified the readme.md exemple :

 

  @Lenses case class Street(name: String, nr: Int)
  @Lenses case class Address(street: Street, city: Option[String])
  @Lenses case class Company(address: List[Address], name: String)
  @Lenses case class Employee(company: Company, id: String)

But I don't know to use Transerval & Optional to manipulate this new version of Employee.

I'm looking for some code exemple.

Regards,
Ronan.

[Julien Truffaut]

Hi Ronan,

Typically you want to use `some: Prism[Option[A], A]` (defined in `monocle.std.option`) to zoom into an `Option`. 

For a `List`, it all depends which elements you want to update, if it is all elements, then you can use `each: Traversal[List[A], A]` (defined in `monocle.function`). Note: `each` is more generic than this, there is an instance for most scala std collection.

So for example if you want to modify all cities you could do:

`(Company.address composeTraversal each composeLens Address.city composePrism some).set("London")(company)`

Please tell me if you have any other questions, you can also come to the gitter channel.

Cheers,

[Ronan Michaux]

I've tried your exemple :

  @Lenses case class Street(name: String, nr: Int)
  @Lenses case class Address(street: Street, city: Option[String])
  @Lenses case class Company(address: List[Address], name: String)
  @Lenses case class Employee(company: Company, id: String)

  val company1 = Company(List(Address(Street("street1", 1), Some("city1"))), "acme")

  import monocle.std.option._
  import monocle.function._
 
  (Company.address composeTraversal each composeLens Address.city composePrism some).set("London")(company1)

But I've got this compile error :

ambiguous implicit values:
both method optEach in trait OptionInstances of type [A]=> monocle.function.Each[Option[A],A]
and method someEach in trait OptionInstances of type [A]=> monocle.function.Each[Some[A],A]
match expected type monocle.function.Each[S,A]

I don't understand my mistake ?

Regards.

[Julien Truffaut]

I can understand, the error message is very unclear. The problem is not that you an ambiguous implicit but that you don't have an instance of `Each[List[A], A]` in scope.

All List instances are in `monocle.std.list` so if you add the following import it should work: `import monocle.std.list._`

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Julien Truffaut

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[Ronan Michaux]

Thank you !