arrow-core/arrow.core.raise/Raise/raise

raise

abstract fun raise(r: Error): Nothing(source)

Raises a logical failure of type Error. This function behaves like a return statement, immediately short-circuiting and terminating the computation.

Alternatives: Common ways to raise errors include: ensure, ensureNotNull, and bind. Consider using them to make your code more concise and expressive.

Handling raised errors: Refer to recover and mapOrAccumulate.

Parameters

an error of type Error that will short-circuit the computation. Behaves similarly to return or throw.

Example:

import arrow.core.Either
import arrow.core.mapOrAccumulate
import arrow.core.raise.*

enum class ServiceType { Free, Paid }

data class Config(val mode: Int, val role: String, val serviceType: ServiceType)

context(Raise<String>)
fun readConfig(): Config {
    val mode = ensureNotNull(readln().toIntOrNull()) {
        "Mode should be a valid integer"
    }
    val role = readln()
    ensure(role in listOf("Manager", "Admin")) {
        "$role should be either a \"Manager\" or an \"Admin\""
    }
    val serviceType = parseServiceType(readln()).bind()

    return Config(
        mode = mode,
        role = role,
        serviceType = serviceType
    )
}

private fun parseServiceType(rawString: String): Either<String, ServiceType> = catch({
    val serviceType = ServiceType.valueOf(rawString)
    Either.Right(serviceType)
}) {
    Either.Left("$rawString is not a valid service type")
}

fun main() {
    val config = recover(::readConfig) { errMsg ->
        error("Invalid config, error: $errMsg")
    }
    // Read 3 additional configs and return Either.Right only if all of them are valid
    val additionalConfigs = (1..3).mapOrAccumulate { readConfig() }
    println(config) // valid Config
    println(additionalConfigs) //  Either<NonEmptyList<String>, List<Config>>
}