`Reader` and `TryReader` monads as demonstrated by Mario Fusco (@mariofusco) Devoxx 2015

Reader.java

public class Reader<R, A> {
    private final Function<R, A> run;

    public Reader(Function<R, A> run) { this.run = run; }

    public <B> Reader<R, B> map(Function<A, B> f) {
        return new Reader<>( r -> f.apply((apply(r))) );
    }

    public <B> Reader<R, B> flatMap(Function<A, Reader<R, B>> f) {
        return new Reader<>( r -> f.apply(apply(r)).apply(r) );
    }

    public A apply(R r) {
        return run.apply(r);
    }
}

TryReader.java

public class TryReader<R, A> {
    private final Function<R, Try<A>> run;
    public TryReader(Function<R, Try<A>> run) { this.run = run; }

    public <B> TryReader<R, B> map(Function<A, B> f) {
        return new TryReader<>(r -> apply(r).map(f::apply));
    }

    public <B> TryReader<R, B> flatMap(Function<A, TryReader<R, B>> f) {
        return new TryReader<>(r -> apply(r).flatMap(a -> f.apply(a).apply(r)));
    }

    public <B> TryReader<R, B> mapReader(Function<A, Reader<R, B>> f) {
        return new TryReader<>(r -> apply(r).map( a -> f.apply(a).apply(r) ) );
    }

    public Try<A> apply(R r) { return run.apply(r); }
}

Slides: http://www.slideshare.net/mariofusco/from-object-oriented-to-functional-domain-modeling
Video: https://www.youtube.com/watch?v=K6BmGBzIqW0