package lrs.visitor;
import lrs.*;

public class Unzip2 implements IAlgo {
    public  Object emptyCase(LRStruct host, Object... inp) {
        return new LRStruct(); 
    }


    /**
     * Returns the odd-indexed elements.
     * Mutates the host to contain only the original even-indexed elements
     */
    public Object nonEmptyCase(LRStruct host, Object... inp) {
        /*
         * host.getRest().execute(this):
         * returns the list that contains the remaining of the even indexed elements of host
         * mutates the host's rest to contain the odd-indexed elements of the original host list.
         */
        LRStruct rest = host.getRest();
        LRStruct remainingEvenOfHost = (LRStruct)rest.execute(this);
        // rest has now mutated to contain the odd indexed elements of the original host.
        host.setRest(remainingEvenOfHost);
        return rest; // to do
    }
}