https://github.com/typelevel/mouse
A small companion to cats
https://github.com/typelevel/mouse
cats scala typelevel
Last synced: 2 months ago
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A small companion to cats
- Host: GitHub
- URL: https://github.com/typelevel/mouse
- Owner: typelevel
- License: mit
- Created: 2016-05-05T13:14:54.000Z (over 9 years ago)
- Default Branch: main
- Last Pushed: 2025-07-06T06:35:17.000Z (3 months ago)
- Last Synced: 2025-07-30T19:17:32.147Z (2 months ago)
- Topics: cats, scala, typelevel
- Language: Scala
- Size: 857 KB
- Stars: 375
- Watchers: 12
- Forks: 65
- Open Issues: 6
-
Metadata Files:
- Readme: README.md
- Contributing: docs/contributing-guide.md
- License: LICENSE
Awesome Lists containing this project
README
# Mouse  [](https://maven-badges.herokuapp.com/maven-central/org.typelevel/mouse_2.12) 
Mouse is a small companion to the [Cats](https://github.com/typelevel/cats) functional programming library and the Scala standard library.
The library arose from this [Cats issue](https://github.com/typelevel/cats/issues/791) and is a [Typelevel member](http://typelevel.org/projects/).
Mouse is published for Scala 2.12, 2.13 and 3.0. For Scala.jvm:
`"org.typelevel" %% "mouse" % version`
For scala.js 1.x:
`"org.typelevel" %%% "mouse" % version`
Learn more about Mouse at https://typelevel.org/mouse/.
## Content
Mouse includes enrichments for:
- [Any](./shared/src/main/scala/mouse/any.scala)
- [Boolean](./shared/src/main/scala/mouse/boolean.scala)
- [Double](./shared/src/main/scala/mouse/double.scala)
- [F\[A\] for any F, A](./shared/src/main/scala/mouse/anyf.scala)
- [F\[Either\[A, B\]\]](./shared/src/main/scala/mouse/feither.scala)
- [F\[Option\[A\]\]](./shared/src/main/scala/mouse/foption.scala)
- [F\[G\[A\]\]](./shared/src/main/scala/mouse/fnested.scala)
- [F\[G\[H\[A\]\]\]](./shared/src/main/scala/mouse/fnested.scala)
- [F\[TupleN\]](./shared/src/main/scala/mouse/ftuple.scala)
- [Int](./shared/src/main/scala/mouse/int.scala)
- [List](./shared/src/main/scala/mouse/list.scala)
- [Long](./shared/src/main/scala/mouse/long.scala)
- [Map](./shared/src/main/scala/mouse/map.scala)
- [Option](./shared/src/main/scala/mouse/option.scala)
- [Set](./shared/src/main/scala/mouse/set.scala)
- [String](./shared/src/main/scala/mouse/string.scala)
- [Try](./shared/src/main/scala/mouse/try.scala)
- [Tuple](./shared/src/main/scala-2/src/main/scala/mouse/tuple.scala)
#### Example:
```scala
scala> import mouse.all._
import mouse.all._
scala> true.option("Its true!")
res0: Option[String] = Some(Its true!)
scala> def makeEven(i: Int) = (i % 2 == 1).applyIf(i)(_ - 1)
def makeEven(i: Int): Int
scala> val e1: Either[String, Int] = Left("failed")
e1: Either[String,Int] = Left(failed)
scala> true.whenA(e1)
res0: Either[String,Unit] = Left(failed)
scala> false.whenA(e1)
res1: Either[String,Unit] = Right(())
scala> res0.cata(msg => s"Message received: ${msg}", "No message")
res1: String = Message received: Its true!
scala> "1.0".parseFloat
res0: Either[NumberFormatException, Float] = Right(1.0F)
scala> "foo".parseIntValidated
res1: cats.data.Validated[NumberFormatException,Int] = Invalid(java.lang.NumberFormatException: For input string: "foo")
scala> val t1 = scala.util.Try(new java.net.URL("https://www.github.com"))
t1: scala.util.Try[java.net.URL] = Success(https://www.github.com)
scala> t1.cata(msg => s"URL is valid!", error => s"URL is invalid: ${error.getMessage}")
res1: String = URL is valid!
scala> t1.toEither
res2: Either[Throwable,java.net.URL] = Right(https://www.github.com)
scala> val t2 = scala.util.Try(new java.net.URL("https//www.github.com"))
t2: scala.util.Try[java.net.URL] = Failure(java.net.MalformedURLException: no protocol: https//www.github.com)
scala> t2.cata(msg => s"URL is valid!", error => s"URL is invalid: ${error.getMessage}")
res3: String = URL is invalid: no protocol: https//www.github.com
scala> t2.toEither
res4: Either[Throwable,java.net.URL] = Left(java.net.MalformedURLException: no protocol: https//www.github.com)
scala> val intToBytes = 123456789.toByteArray
intToBytes: Array[Byte] = Array(7, 91, -51, 21)
scala> val longToBase64 = 123456789L.toBase64
longToBase64: String = AAAAAAdbzRU
scala> 5.squared
res0: Int = 25
scala> 1.5 |> (_.toInt) |> (_.toString)
res0: String = 1
//lift a partial function into a total function to an Either, when you want to treat unhandled input cases as an error
scala> liftEither[Option[Int]]({case Some(n) => n}, a => s"Unexpected: $a")(Some(6))
res0: Either[String,Int] = Right(6)
scala> val mapped = Map(1 -> 2, 3 -> 4).mapKeys(_ * 2)
mapped: Map[Int,Int] = Map(2 -> 2, 6 -> 4)
scala> val foption = List(Option(1), Option(2), Option(4)).mapIn(_ * 2)
foption: List[Option[Int]] = List(Some(2), Some(4), Some(8))
scala> val feither = List(Either.cond(true, 1, "0")).mapIn(_ * 2)
feither: List[Either[String, Int]] = List(Right(2))
scala> val listOption = List(Option(1), Option(2)).mapNested2(_ * 2)
listOption: List[Option[Int]] = List(Some(2), Some(4))
scala> val listOptionList = List(Option(List(1)), Option(List(2))).mapNested3(_ * 2)
listOptionList: List[Option[List[Int]]] = List(Some(List(2)), Some(List(4)))
scala> val tupleHead = (1, 2, 4, 8).head
tupleHead: Int = 1
scala> val tupleLast = (1, 2, 4, 8).last
tupleLast: Int = 8
scala> Set(0).tailOrEmpty
val res3: Set[Int] = Set()
scala> Nil.tailOrEmpty
val res1: List[Nothing] = List()
scala> Set(0).tailOption
val res4: Option[cats.data.NonEmptySet[Int]] = None
scala> List(0,1,2).tailOption
val res5: Option[cats.data.NonEmptyList[Int]] = Some(NonEmptyList(1, 2))
```
## Scope of Library
- Provide enrichments to classes from the Scala standard library that convert to Cats datatypes,
or otherwise improve the functional programming experience.
## Contributing
Mouse is maintained by @benhutchison and @danicheg.
Issues and pull requests are welcome. Code contributions should be aligned with the above scope to be included, and include unit tests.
See [contributing guide](./DEV.md) for more details.
This project supports the [Scala code of conduct](https://www.scala-lang.org/conduct/) and aims that its channels
(mailing list, Gitter, github, etc.) to be welcoming environments for everyone.