package brs.visitor;

import brs.*;
import utils.fp.*;

public class InOrder implements IVisitor {

    /**
     * Object -> (Object -> (Object -> Object))
     */
    private ILambda _combine;

    public InOrder(ILambda process) {
        _combine = process;
    }

    /**
     * @param inp an ILambda to process the data Objects in host.
     * inp.apply(null) must be defined.
     */
    public Object emptyCase(BiTree host, Object inp) {
        return ((ILambda)inp).apply(null);
    }

    /**
     * Processes the left subtree, the root and the right subtree.  Combines the
     * results.  See S02 code for BSTDictionary for an example of printing the
     * the tree in order by usign a lambda that concatenates the 3 results.
     * @param inp an ILambda to process the data Objects in host.
     * inp.apply(null) must be defined.
     */
    public Object nonEmptyCase(BiTree host, Object inp) {
        ILambda f = (ILambda)inp;
        return
            ((ILambda)((ILambda)_combine.apply(
                host.getLeftSubTree().execute(this, inp))).apply(
                    f.apply(host.getRootDat()))).apply(
                        host.getRightSubTree().execute(this, inp));

    }
}