observar.java

package foo.bar;

import static com.htravel.fp.Parsers.maybeInt;
import static java.util.stream.Collectors.toList;

import com.htravel.fp.Either;
import java.util.stream.IntStream;
import rx.Observable;

public class Observar {

    public static void main(String... args) {
        makeMake("7")
                .subscribe(x -> x.then(
                        e -> eco("Error: %s, ", e),
                        o -> o.subscribe(z -> eco("Success: %s, ", z))
                ));
    }

    private static void eco(String format, Object... args) {
        System.err.printf(format, args);
        System.err.flush();
    }

    private static Either<String, Observable<Integer>> make(String configuration) {
        return maybeInt(configuration)
                .guard(n -> n > 0 && n < 10, n -> String.format("bad '%s' configuration", n))
                .map(n -> IntStream.range(0, n).boxed().collect(toList()))
                .map(Observable::from);
    }

    private static Observable<Either<String, Observable<Integer>>> makeMake(String configuration) {
        return make(configuration)
                .map(o -> o.map(z -> make(Integer.toString(2 * z))))
                .left2right(x -> Observable.empty()); // <<<< when Left then Right using Empty
    }
}