more_lambdas.js

append = function(el, list) {
    if (is_empty(list)) {
        return prepend(el, list);
    } else {
        return prepend(head(list), append(el, tail(list)));
    }
};

last = function(list) {
    if (is_empty(tail(list))) {
        return head(list);
    } else {
        return last(tail(list));
    }
};