I've got the following problem: I have a tree of objects of different classes where an action in the child class invalidates the parent. In imperative languages, it is trivial to do. For example, in Java:
public class A {
private List<B> m_children = new LinkedList<B>();
private boolean m_valid = true;
public void invalidate() {
m_valid = false;
}
public void addChild(B child) {
m_children.add(child);
child.m_parent = this;
}
}
public class B {
public A m_parent = null;
private int m_data = 0;
public void setData(int data) {
m_data = 0;
m_parent.invalidate();
}
}
public class Main {
public static void main(String[] args) {
A a = new A();
B b = new B();
b.setData(0); //invalidates A
}
}
How do I do the above in Haskell? I cannot wrap my mind around this, since once I construct an object in Haskell, it cannot be changed.
I would be much obliged if the relevant Haskell code is posted.
