willMatchWith

Limited pattern matching for futures.

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?)

forall a, b, c, d:
  type Pattern = { r |
    Cancelled: ()  => Future c d,
    Resolved:  (b) => Future c d,
    Rejected:  (a) => Future c d
  }
  
  (Future a b).(Pattern) => Future c d

Documentation

Limited pattern matching for futures.

Example:

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

of(1).willMatchWith({
  Cancelled: () => of('no'),
  Rejected:  (x) => of(x + 1),
  Resolved:  (x) => of(x - 1)
}).listen({
  onResolved: (x) => $ASSERT(x == 0)
});


rejected(1).willMatchWith({
  Cancelled: () => of('no'),
  Rejected:  (x) => of(x + 1),
  Resolved:  (x) => of(x - 1)
}).listen({
  onResolved: (x) => $ASSERT(x == 2)
})

Properties

Source Code

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

willMatchWith(pattern) {
    let deferred = new Deferred();      // eslint-disable-line prefer-const
    const resolve = (handler) => (value) => handler(value).listen({
      onCancelled: ()         => deferred.cancel(),
      onResolved:  (newValue) => deferred.resolve(newValue),
      onRejected:  (reason)   => deferred.reject(reason) 
    });
    this.listen({
      onCancelled: resolve(pattern.Cancelled),
      onResolved:  resolve(pattern.Resolved),
      onRejected:  resolve(pattern.Rejected)
    });

    return deferred.future();
  }