cyclops monad api : flatMap on Optional returns a Stream (or flatMap from a single valued monad returning a multi valued monad)

Cyclops has merged with simple-react. Please update your bookmarks (stars :) ) to https://github.com/aol/cyclops-react

All new develpoment on cyclops occurs in cyclops-react. Older modules are still available in maven central.

AnyM is an abstraction over any monad type, some monads such as CompletableFuture & Optional hold a single value (collections in this case are still treated as a single value) while others such as Stream and List can hold multiple values. In Cyclops the AnyM type follows the type of the underlying monad, that is

Stream<Integer> stream = Stream.of(1,2,3);

corresponds to 

AnyM<Integer> anyM = AnyM.fromStream(stream);

Stream<Integer> corresponds to AnyM<Integer>

Similarly

Optional<Integer> optional = Optional.of(1);

corresponds to 

AnyM<Integer> anyM = AnyM.fromStream(optional);

Optional<Integer> corresponds to AnyM<Integer>

Returning a Stream in the flatMap method of Optional requires either that we select only a single value from the Stream or change our return type on the flatMap. To see the required signature change

Optional.of(1,2,3).flatMap(i->Stream.of(1,2,3,4)) 

implies something like

Optional<List<Integer>>

rather than Optional<Integer>

As we can't change the signature, we simply select the first value from the Stream. In this regard we follow the same rules as Javaslang