package schemeFactory.visitor;

import schemeFactory.*;

public class Zipper implements IListAlgo {

    private IListFactory _fact;

    public Zipper(IListFactory f) {
        _fact = f;
    }

    /**
     * Weaving an empty list with inp results in inp alone.
     * @param inp the other AList to be weaved with host.
     * @return AList
     */
    public Object emptyCase(AList host, Object inp) {
        return inp;
    }

    /**
     * Recursively weave inp with host's rest.  Then "cons"
     * host's first with the result.
     * @param inp the other AList to be weaved with host.
     * @return AList
     */
    public Object nonEmptyCase(AList host, Object inp) {
        Object zipRest = ((AList)inp).execute(this, host.getRest());
        return _fact.makeNEList(host.getFirst(), (AList)zipRest);
    }
}