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src cyclops core upgrade Mar 18, 2018


Vavr Integration


Get cyclops-javaslang


  • Fast, lazy Xtended Collection support for Vavr Persistent collections (see Faster Purely Functional Data Structues )
    • Async / reactive collections with optional non-blocking backpressure via Spouts
  • Conversion between Vavr types and other Functional libraries (including Vavr Future to reactive Maybe, Either, Eval types)
  • Native for comprehensions for Vavr types with an intuitive and clean API
  • AnyM monad wrapper for Monadic types (with full integration with cyclops-react Monad abstractions such as Kleisli)
    • Mix and match functional libraries at will taking full advantage of the features of each. E.g. Mix reactive Observables, pushing asynchronously to Vavr collections
  • Companion classes for Vavr types offering :
    • For comprehensions
    • Higher Kinded Typeclasses
    • Semigroups and Monoids
    • Helper functions for combining / accumulating and zipping values

Xtended Collections

Create and convert a Vavr Vector via Xtended Collections

 Vector<Integer> vector = VectorX.of(1, 2, 3)
                                .map(i -> i * 2)

Asynchronously populate a Vavr Vector

 VectorX<Integer> vectorX = Spouts.reactive(Stream.of(1, 2, 3),Executors.newFixedThreadPool(1))
				  .materialize();//kick of the async population

/** Continue processing **/

vectorX.get(1); //blocking operation until data loaded

//or unwrap back to Vavr

Vector<Integer> vavr = vector.to(VavrConverters::Vector);

Monad Transformers

 ListT<option,Integer> vectorInOption = ListT.ofList(Vavr.option(Option.some(VavrVectorX.of(10))));

        ListT<option,Integer> doubled = vectorInOption.map(i->i*2);
        ListT<option,Integer> repeated = doubled.cycle(3);

        //ListT[Some([20, 20, 20])]
        Option<Vector<Integer>> list = option(vectorInOption.unwrap()).map(s -> s.to()

For Comprehensions

Try<String> result = Trys.forEach4(grind("arabica beans"),
                                    ground -> heatWater(new Water( 25)),
                                    (ground, water) -> brew(ground, water),
                                    (ground, water ,espresso) -> frothMilk("milk"),
                                    (ground , water ,espresso , foam) -> combine(espresso, foam));

        Try<String> grind(String beans) {  return Try.of(() -> "ground coffee of " + beans);}
        Try<Water> heatWater(Water water) { return Try.of(() -> water.withTemperature(85)); }
        Try<String> frothMilk(String milk) { return Try.of(() -> "frothed " + milk);}
        Try<String> brew(String coffee, Water heatedWater) { return Try.of(() -> "espresso");}
        String combine(String espresso, String frothedMilk) { return "cappuccino"; }

Reactive Either / Maybe / Eval (from cyclops-react)

Asynchronously push data into a cyclops-react either from a Vavr Future

import static cyclops.conversion.vavr.ToCyclopsReact.either;

Either<Throwable,String> result = either(Future.of(Executors.newFixedThreadPool(1),this::loadData));


AnyM : a type safe abstraction across Any Monadic type in Java.

Define ulta-generic code that can be used by types across Vavr, Reactor, cyclops-react, Guava, JDK, Functional Java, RxJava.

public <W extends WitnessType<W>> AnyMSeq<W,Integer> sumAdjacent(AnyMSeq<W,Integer> sequence){
     return sequence.sliding(1)

Use them with Vavr

import static cyclops.monads.VavrWitness.list;
import cyclops.companion.vavr.Lists;

AnyMSeq<list,Integer> vavrList = Lists.anyM(List.range(0, 10));
AnyMSeq<list,Integer> summedVavr = sumAdjacent(vavrList);
List<Integer> backToVavr = VavrWitness.list(summedVavr);

Or RxJava

import static cyclops.monads.Rx2Witness.observable;
import cyclops.companion.rx.Observables;

AnyMSeq<observable,Integer> rxObservable = Observables.anyM(Observable.range(0, 10));
AnyMSeq<observable,Integer> summedRx = sumAdjacent(rxObservable);
Observable<Integer> backToRx = RxWitness.observable(summedRx);

Schedule emission from Vavr Stream

import static cyclops.monads.Vavr.stream;

stream(Stream.ofAll(1,2,3)).schedule("* * * * * ?", Executors.newScheduledThreadPool(1))

Use Vavr. to wrap Vavr Monads

			.toList(),equalTo(Arrays.asList("HELLO WORLD")));

Kotlin style sequence generators

import static com.oath.cyclops.types.foldable.ConvertableSequence.Conversion.LAZY;
import static cyclops.stream.Generator.suspend;
import static cyclops.stream.Generator.times;

i = 100;
k = 9999;

Vector<Integer> vec = suspend((Integer i) -> i != 4, s -> {

                         Generator<Integer> gen1 = suspend(times(2), s2 -> s2.yield(i++));
                         Generator<Integer> gen2 = suspend(times(2), s2 -> s2.yield(k--));

                         return s.yieldAll(gen1.stream(), gen2.stream());

//Vector(100, 101, 9999, 9998, 102)

Higher Kinded Typeclasses

cyclops provides the following Typeclasses and implementations for many Vavr Types

  • Unit / pure
  • Functor
  • Applicative
  • Monad
  • MonadZero
  • MonadPlus
  • Comonad
  • Foldable
  • Unfoldable
  • Eq
  • Traverse

Instances are provided for the following Vavr types : Stream, List, Vector, Array, Queue, HashSet, Option, Try, Future, Either

Type class instances are accessible through the Companion Object for each type.

Using Typeclasses


Typeclasses can be used directly (although this results in verbose and somewhat cumbersome code) e.g. using the Pure and Functor typeclasses for Vavr Streams

   Pure<stream> pure = Streams.Instances.unit();
   Functor<stream> functor = Streams.Instances.functor();
   StreamKind<Integer> stream = pure.unit("hello")
                                  .applyHKT(h->functor.map((String v) ->v.length(), h))


Via Active

The Active class represents a Higher Kinded encoding of a Vavr (or cyclops-react/ JDK/ reactor / rx etc) type and it's associated type classes

The code above which creates a new Stream containing a single element "hello" and transforms it to Stream of Integers (the length of each word), can be written much more succintly with Active

Active<stream,Integer> active = Streams.allTypeClasses(Stream.empty());

Active<stream,Integer> hello = active.unit("hello")

Stream<Integer> stream = StreamKind.narrow(hello.getActive());

Via Nested

The Nested class represents a Nested data structure, for example a List of Options and the associated typeclass instances for both types.

import cyclops.companion.vavr.Options.OptionNested;

Nested<option,list,Integer> optList  = OptionNested.list(Option.some(List.ofAll(1,10,2,3)))
                                                                       .map(i -> i * 20);

Option<Integer> opt  = optList.foldsUnsafe()


Via Coproduct

Coproduct is a Sum type for HKT encoded types that also stores the associated type classes

import static 
Coproduct<list,option,Integer> nums = Options.coproduct(10,Lists.Instances.definitions());

int value = nums.map(i->i*2)