benhutchison / mouse   0.10-MF

MIT License GitHub

A small companion to cats

Scala versions: 2.12 2.11 2.10
Scala.js versions: 0.6


Mouse is a small companion to the Cats functional programming library for Scala. It includes convenience extension methods for Scala standard library classes, including some found in scalaz that are not in Cats.

The library arose from this Cats issue and is a Typelevel member.

Mouse is published for Scala 2.12 and 2.13. For Scala.jvm:

"org.typelevel" %% "mouse" % version

For scala.js 1.x:

"org.typelevel" %%% "mouse" % version

Maven Central

Build Status


Mouse includes enrichments for:


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> 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:[NumberFormatException,Int] = Invalid(java.lang.NumberFormatException: For input string: "foo")

scala> val t1 = scala.util.Try(new""))
t1: scala.util.Try[] = Success(

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,] = Right(

scala> val t2 = scala.util.Try(new"https//"))
t2: scala.util.Try[] = Failure( no protocol: https//

scala> t2.cata(msg => s"URL is valid!", error => s"URL is invalid: ${error.getMessage}")
res3: String = URL is invalid: no protocol: https//

scala> t2.toEither
res4: Either[Throwable,] = Left( no protocol: https//

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)

Release Notes

Version 0.26 (Dec 20) adds applyIf for Boolean and builds against Cats 2.3.0.

Version 0.25 (Apr 20) adds Scalajs 1.x support.

Version 0.24 (Dec 19) adds valueOrPure for Boolean and parseUrl/parseUri for String. Drops 2.11 support. Built against cats 2.1.0.

Version 0.23 (Aug 19) adds parsing of BigInt and BigDecimal. Built against cats 2.0.0-RC1.

Version 0.22 (June 19) is about support for Scala 2.13.0. Built against cats 2.0.0-M4.

Version 0.21 (May 19) is about support for Scala 2.13.0 RC1. Built against cats 2.0 M1.

Version 0.20 (Dec 18) adds syntax for Map and add support for Scala 2.13.0 M5. Built against cats 1.5.0.

Version 0.19 (Oct 18) adds syntax for F[A] and is built against cats 1.4.0. Support for Scala 2.10 is removed in this release.

Version 0.18 (Aug 18) adds PartialFunction lift to Either and is built against cats 1.2.0

Version 0.17 (Apr 18) is built against cats 1.1.0

Version 0.16 (Jan 18) is built against cats 1.0.1

Version 0.15 (Dec 17) is built against cats 1.0.0

Version 0.14 (Dec 17) include Int/Long/Double squared and is built against cats 1.0.0-RC2

Version 0.13 (Dec 17) include Int/Long/Double toByteArray and toBase64 operations and is built against cats 1.0.0-RC1

Version 0.12 (Nov 17) include Boolean Monoid operations and is built against cats 1.0.0-RC1

Version 0.11 (Oct 17) migrates to org.typelevel group and remains built against cats 1.0.0-MF

Version 0.10-MF (Aug 17) is built against cats 1.0.0-MF. It mainly supports compat testing for cats 1.0 release.

Version 0.9 (Jun 17) is built against cats 0.9, rename either->toEither on Try to align with 2.12 core changes.

Version 0.8 (Jun 17) is built against cats 0.9, cata and either on Try.

Version 0.7 (Apr 17) is built against cats 0.9, Boolean fold, Option right and left.

Version 0.6 (Nov 16) is built against cats 0.8.1 and migrates Xor boolean syntax to Either.

Version 0.5 (Aug 16) is built against cats 0.7.0 but otherwise unchanged.

Version 0.4 (July 2016) includes a breaking package rename from com.github.benhutchison.mouse -> mouse. Rationale was to follow cats and other modern libs convention of short, convenient package names.

Scope of Library

  • Provide enrichments to classes from the Scala standard library that convert to Cats datatypes, or otherwise improve the functional programming experience.

  • Make it easier to migrate source code between Scalaz and Cats.


Issues and pull requests are welcome. Code contributions should be aligned with the above scope to be included, and include unit tests.

This project supports the Scala code of conduct and aims that its channels (mailing list, Gitter, github, etc.) to be welcoming environments for everyone.