gistfile1.java

/* POC code, abstract classes might be better */

interface RootObject {}
class Machine implements RootObject {
        private Agent agent;
        private Machine parent;

        public Machine(Agent agent) {
                this.agent = agent;
                this.parent = null;
        }

        public Machine(Agent agent, Machine parent) {
                this(agent);
                this.parent = parent;
        }

        public Machine getParent() {
                return this.parent;
        }

        public Agent getAgent() {
                return this.agent;
        }                
}

class Agent implements RootObject {
        private String name;

        public Agent(String name) {
                this.name = name;
        }

        public String getName() {
                return this.name;
        }
}

interface Applicable {
        public RootObject apply(RootObject o);
}

class agent implements Applicable {
        private Applicable child;

        public agent() {
                this.child = null;
        }

        public agent(Applicable a) {
                this.child = a;
        }

        public RootObject apply(RootObject o) {
                RootObject real_o = null;

                if(this.child != null)
                        real_o = this.child.apply(o);
                else
                        real_o = o;

                Machine m = (Machine)real_o;

                return m.getAgent();
        }
}

class parent implements Applicable {
        private Applicable child;

        public parent() {
                this.child = null;
        }

        public parent(Applicable a) {
                this.child = a;
        }

        public RootObject apply(RootObject o) {
                RootObject real_o = null;

                if(this.child != null)
                        real_o = this.child.apply(o);
                else
                        real_o = o;

                Machine m = (Machine)real_o;

                return m.getParent();
        }
}

class DSL {
        public static void main(String[] args) {
                Applicable res = new agent(new parent(new parent()));

                Machine m1 = new Machine(new Agent("agent1"));
                Machine m2 = new Machine(new Agent("agent2"), m1);
                Machine m3 = new Machine(new Agent("agent3"), m2);

                Agent a = (Agent)res.apply(m3);
                System.out.println("Name: " + a.getName());
        }
}