Safe App type that executes a IO. Shutdown occurs after the IO completes, as follows:

- If completed with ExitCode.Success, the main method exits and shutdown is handled by the platform.

- If completed with any other ExitCode, sys.exit is called with the specified code.

- If the IO raises an error, the stack trace is printed to standard error and sys.exit(1) is called.

When a shutdown is requested via a signal, the IO is canceled and we wait for the IO to release any resources. The process exits with the numeric value of the signal plus 128.

import cats.effect._
import cats.implicits._
import monix.bio._

object MyApp extends BIOApp {
  def run(args: List[String]): UIO[ExitCode] =
    args.headOption match {
      case Some(name) =>
        UIO(println(s"Hello, \${name}.")).as(ExitCode.Success)
      case None =>
        UIO(System.err.println("Usage: MyApp name")).as(ExitCode(2))
    }
}

N.B. this is homologous with cats.effect.IOApp, but meant for usage with IO.

Works on top of JavaScript as well ;-)