orElse

Transforms a failed task's value and state.

This feature is experimental!

This API is still experimental, so it may change or be removed in future versions. You should not rely on it for production applications.

Signature

value(handler)

Type(what is this?)

forall e, e2, v:
  (Task e v).((e) => Task e2 v) => Task e2 v

Documentation

Transforms a failed task's value and state.

Example:

const { of, rejected } = require('folktale/concurrency/task');

const hello = of('hello').orElse(error => of('world'));
const result1 = await hello.run().promise();
$ASSERT(result1 == 'hello');

const world = rejected('hello').orElse(error => of('world'));
const result2 = await world.run().promise();
$ASSERT(result2 == 'world');

const helloWorld = rejected('hello').orElse(error => rejected(error + ' world'));
try {
  const result3 = await helloWorld.run().promise();
  throw 'never happens';
} catch (error) {
  $ASSERT(error == 'hello world');
}

Properties

Source Code

Defined in source/concurrency/task/_task.js at line 20, column 0

orElse(handler) {
    return new Task(resolver => {
      const execution = this.run();
      resolver.onCancelled(() => execution.cancel());

      execution.listen({
        onCancelled: resolver.cancel,
        onResolved:  resolver.resolve,
        onRejected:  reason => {
          execution.link(handler(reason).run().listen({
            onCancelled: resolver.cancel,
            onRejected:  resolver.reject,
            onResolved:  resolver.resolve
          }));
        }
      });
    });
  }