list_new := ??{
	x := {
		front := nil;
		back := nil;
	};
};

list_push_front := ??(list, item){
	list {
		if front == nil {
			front = {
				value := item;
				next := nil;
				prev := nil;
			};
			back = front;
		} else {
			front = {
				value := item;
				next := front;
				prev := nil;
			};
		}
	}
};

list_push_back := ??(list, item){
	list {
		if back == nil {
			front = {
				value := item;
				next := nil;
				prev := nil;
			};
			back = front;
		} else {
			back = {
				value := item;
				next := nil;
				prev := back;
			};
		}
	}
};

list_pop_front := ??(list){
	x := nil;
	list {
		if front == nil {
			throw_error("Call to 'list_pop_front' on empty list");
		}
		front {
			x = value;
			front = next;
		}
		if front == nil {
			back = nil;
		}
	}
};

list_pop_back := ??(list){
	x := nil;
	list {
		if back == nil {
			throw_error("Call to 'list_pop_back' on empty list");
		}
		back {
			x = value;
			back = prev;
		}
		if back == nil {
			front = nil;
		}
	}
};

list_get := nil;
{
	get_helper := ??(front, idx){
		if front == nil {
			throw_error("Index past end of list in 'list_get'");
		}
		y := nil;
		if idx == 0 {
			front {
				y = value;
			}
		} else {
			front {
				get_helper(next, idx - 1) {y = x;}
			}
		}
		x := y;
	};
	list_get = ??(list, idx){
		if idx < 0 {
			throw_error("Negative index in 'list_get'");
		}
		y := nil;
		list {
			get_helper(front, idx) {y = x;}
		}
		x := y;
	};
};

list_set := nil;
{
	set_helper := ??(front, idx, val){
		if front == nil {
			throw_error("Index past end of list in 'list_set'");
		}
		if idx == 0 {
			front {
				value = val;
			}
		} else {
			front {
				set_helper(next, idx - 1, val);
			}
		}
	};
	list_set = ??(list, idx, val){
		if idx < 0 {
			throw_error("Negative index in 'list_set'");
		}
		list {
			set_helper(front, idx, val);
		}
	};
};