Red black trees with classes in OCaml - class

Question

Does anyone know how to implement red black trees with classes in OCaml?
At least the class properties and initializers? I'm new in OCaml.
What I tried:
type data = {key: int; value: string}
class node (data: data) =
object (self)
val mutable d = data
val mutable color = 1
val mutable left = ref (None: node option)
val mutable right = ref (None: node option)
val mutable parent = ref (None: node option)
method getLeft = left
method getRight = right
method getParent = parent
method getColor = color
method getData = d
method setLeft (l: node option ref) = left := !l
method setRight (l: node option ref) = right := !l
method setParent (l: node option ref) = parent := !l
end;;
class rbtree =
object (self)
val mutable root = ref (None: node option)
val mutable nullNode = ref (None: node option)
method searchNode (aNode: node option ref) (key: data) = begin
if aNode = nullNode || key == (!aNode)#getData then aNode;
end;
end;;
I get the error This expression has type node option
It has no method getData
What I am trying is to make something like this code that is written in C++:
struct Node
{
int data;
Node *parent;
Node *left;
Node *right;
int color;
};
typedef Node *NodePtr;
class RedBlackTree
{
private:
NodePtr root;
NodePtr TNULL;
void initializeNULLNode(NodePtr node, NodePtr parent)
{
node->data = 0;
node->parent = parent;
node->left = nullptr;
node->right = nullptr;
node->color = 0;
}
NodePtr searchTreeHelper(NodePtr node, int key)
{
if (node == TNULL || key == node->data)
{
return node;
}
if (key < node->data)
{
return searchTreeHelper(node->left, key);
}
return searchTreeHelper(node->right, key);
}
};

Answer 1

For the error you're seeing, #Shon is correct. You have this expression:
if aNode = nullNode || key == (!aNode)#getData then aNode;
The type of aNode is node option ref. So that means the type of !anode is node option. An option value isn't an object (an instance of a class). So you can't call the method getData on it.
Again, as #Shon says, you need to retrieve the value of !aNode (if there is one). This will give you a node, which is an object and does have a getData method.
It would be messy to write this code in-line in your if test. So you might write a function like this:
let node_option_has_value node_opt value =
match node_opt with
| None -> false
| Some node -> node#getData = value
As a side comment, you should not be using the physical equality operator (==) to do comparisons. This operator is for special cases, not for general use.
The equality comparison operator in OCaml is = (as in my example code).