---

name: Scala Development description: Senior Scala developer using functional programming and Typelevel ecosystem. Use when writing Scala code, implementing Scala features, or working with sbt/bloop projects. Used as a part of the XP skill.

Scala Development

Principles

• Functional programming techniques
• Avoid Any, null, throw, and unsafe patterns
• Prefer Typelevel ecosystem (cats, cats-effect, fs2)
• Use ADTs for domain modelling
• Errors as values (Either, EitherT, MonadError)

Compilation Priority

1. Check for .bloop directory first (ls -la)

If .bloop exists — use bloop:

Copybloop compile <module-name>
bloop test <module-name>
bloop test <module-name> -o "*<filename>*"

Module name is root for non-modular projects.

If no .bloop — use sbt:

Copysbt compile
sbt test
sbt "testOnly *SpecName*"

1. ALWAYS run sbt commitCheck after completing code changes.

Testing (MUnit)

Copyclass FeatureSpec extends munit.FunSuite:

  test("describes expected behaviour") {
    // Arrange
    val input = createTestData()

    // Act
    val result = functionUnderTest(input)

    // Assert
    assertEquals(result, expected)
  }

Effectful tests (cats-effect):

Copyclass FeatureSpec extends munit.CatsEffectSuite:

  test("async operation succeeds") {
    for
      result <- asyncOperation()
    yield assertEquals(result, expected)
  }

Assertions:

• assertEquals(obtained, expected)
• assertNotEquals(obtained, unexpected)
• assert(condition)
• interceptMessage[ExceptionType]("message") { code }

Error Handling Patterns

Copy// Prefer Either over exceptions
def parse(input: String): Either[ParseError, Value] = ???

// Use EitherT for effectful errors
def fetchAndParse(id: Id): EitherT[IO, AppError, Value] = ???

// MonadError for generic error handling
def process[F[_]: MonadError[*[_], Throwable]](input: Input): F[Output] = ???