listen

Adds a visitor to the Future, which will be invoked when the Future's state changes.

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(pattern)

Type(what is this?)

(Future 'f 's).(DeferredListener 'f 's) => Future 'f 's

Documentation

Adds a visitor to the Future, which will be invoked when the Future's state changes.

Listen allows reacting to changes in a Future, but is very imperative. In general, it's better to use willMatchWith or a more specialised method (like .chain or .orElse) instead.

Example:

const { of } = require('folktale/concurrency/future');

of('hello').listen({
  onCancelled: ()       => { throw 'never happens' },
  onRejected:  (reason) => { throw 'never happens' },
  onResolved:  (value)  => { $ASSERT(value == 'hello') }
});

Properties

Source Code

Defined in source/concurrency/future/_future.js at line 24, column 0

listen(pattern) {
    this._state.matchWith({
      Pending:   ()           => this._listeners.push(pattern),
      Cancelled: ()           => pattern.onCancelled(), 
      Resolved:  ({ value })  => pattern.onResolved(value),
      Rejected:  ({ reason }) => pattern.onRejected(reason)
    });
    return this;
  }