LeftRight.java

LeftRight.java

public final static class Left<LL, LR> extends Either<LL, LR>{
    LL l;
    public Left(LL l) {
        this.l = l;
    }
    @Override
    public <T> T match(Function<LL, T> a, Function<LR, T> b) {
        return a.apply(l);
    }
    @Override
    public <S> Either<LL, S> bind(Function<LR, Either<LL, S>> f) {
        //f cannot be applied, simply return Left value for new Either type
        return new Left<>(l);
    }
    @Override
    public <S> Either<LL, S> fmap(Function<LR, S> f) {
        //f cannot be applied, simply return Left value for new Either type
        return new Left<>(l);
    }
}
    
public final static class Right<RL,RR> extends Either<RL, RR>{
    RR r;
    public Right(RR r) {
        this.r = r;
    }
    @Override
    public <T> T match(Function<RL, T> a, Function<RR, T> b) {
        return b.apply(r);
    }
    @Override
    public <S> Either<RL, S> bind(Function<RR, Either<RL, S>> f) {
        //RR value available, apply f!
        return f.apply(r);
    }
    @Override
    public <S> Either<RL, S> fmap(Function<RR, S> f) {
        //RR value available, apply f & make an new Right value for new Either type
        return new Right<>(f.apply(r));
    }
}