arrow-core/arrow.core.computations/EitherEffect/ensure

ensure

open suspend fun ensure(value: Boolean, orLeft: () -> E)

Ensure check if the value is true, and if it is it allows the either { } binding to continue. In case it is false, then it short-circuits the binding and returns the provided value by orLeft inside an Either.Left.

import arrow.core.computations.either

//sampleStart
suspend fun main() {
  either<String, Int> {
    ensure(true) { "" }
    println("ensure(true) passes")
    ensure(false) { "failed" }
    1
  }
//sampleEnd
  .let(::println)
}
// println: "ensure(true) passes"
// res: Either.Left("failed")