arrow-core/arrow.core.continuations/EagerEffectScope/ensure

ensure

open suspend fun ensure(condition: Boolean, shift: () -> R)

ensure that condition is true, if it's false it will shift with the provided value R. Monadic version of kotlin.require.

import arrow.core.Either
import arrow.core.continuations.eagerEffect
import io.kotest.matchers.shouldBe

fun main() {
  val condition = true
  val failure = "failed"
  val int = 4
  eagerEffect<String, Int> {
    ensure(condition) { failure }
    int
  }.toEither() shouldBe if(condition) Either.Right(int) else Either.Left(failure)
}