Hamsters is finally available for Scala 3 !

After a long wait, I’m happy to announce that Hamsters, the mini Scala utility library, has been ported to Scala 3!

The new 4.0.0 release is built for Scala 3 (3.3.x LTS) and cross-compiled for the JVM and Scala.js. The goal of the library hasn’t changed: provide a lightweight library with a small, focused set of functional utilities that stay approachable, even for people who are just getting started with functional programming.

To add it to your project:

libraryDependencies += "io.github.scala-hamsters" %% "hamsters" % "4.0.0"

Or for a Scala.js project:

libraryDependencies += "io.github.scala-hamsters" %%% "hamsters" % "4.0.0"

A quick tour

Here is a reminder of a few things Hamsters can do for you.

Validation and error handling

Accumulate several validation errors instead of failing on the first one:

import io.github.hamsters.Validation
import Validation._

val e1 = Valid(1)
val e2 = Invalid("error 1")
val e3 = Invalid("error 2")
val e4 = Valid("4")

Validation.run(e1, e2, e3)
// Invalid(List("error 1", "error 2"))

Validation.run(e1, e4)
// Valid((1, "4"))

You can also turn exceptions into values with fromCatchable:

def compute(x: Int): Int = 2 / x

fromCatchable(compute(1)) // Valid(2)
fromCatchable(compute(0)) // Invalid("/ by zero")

You can also extract just the successes or just the failures from a set of validations with Validation.successes and Validation.failures.

Monad transformers

Composing Future[Option[_]] or Future[Either[_, _]] in a for-comprehension is painful by hand. Hamsters gives you FutureOption and FutureEither to flatten the layers:

import io.github.hamsters.FutureEither
import io.github.hamsters.MonadTransformers._

def fea: Future[Either[String, Int]] = Future(Right(1))
def feb(a: Int): Future[Either[String, Int]] = Future(Right(a + 2))

val composedAB: Future[Either[String, Int]] = for {
  a <- FutureEither(fea)
  ab <- FutureEither(feb(a))
} yield ab

And more

Beyond validation and monad transformers, the library also ships:

• mapN to combine multiple values
• Lenses
• Memoization
• NonEmptyList
• Retry helpers
• Default values for options (orEmpty)
• Future squashing (nested type simplifications)
• And more

Have a look at the README and the docs for the full list. Contributions and feedback are, as always, very welcome!