raise

open override 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

r

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>>
}