Monocle · Access and transform immutable data

Monocle is a Scala library which offers a simple yet powerful API to access and transform immutable data.

import monocle.syntax.all._

val user = User("Anna", Address(12, "high street"))

user.focus(_.name).replace("Bob")
// res: User = User("Bob", Address(12, "high street"))

user.focus(_.address.streetName).modify(_.toUpperCase)
// res: User = User("Anna", Address(12, "HIGH STREET"))

user.focus(_.address.streetNumber).get
// res: Int = 12

Installation

Monocle is published for Scala 2.13.x and 3.x. You can add it to your sbt build with:

libraryDependencies ++= Seq(
 "dev.optics" %% "monocle-core"  % "3.1.0",
 "dev.optics" %% "monocle-macro" % "3.1.0",
)

You also need this compiler option if you want to use macro annotations - only available for Scala *2.13:

Global / scalacOptions += "-Ymacro-annotations"

Copyright and license

All code is available to you under the MIT license, available here. The design is informed by many other projects, in particular Haskell Lens.