# stack.nas
# valkmjolnir 2021/3/31
var stack=func(){
    var vec=[];
    return{
        push:func(elem){
            append(vec,elem);
        },
        pop:func(){
            return pop(vec);
        },
        top:func(){
            if(size(vec)!=0)
                return vec[-1];
        },
        clear:func(){
            vec=[];
        },
        empty:func(){
            return size(vec)==0;
        }
    };
}