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

list_push_front := ??(list, item){
	list {
		if front == nil then {
			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 then {
			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 then {
			throw_error("Call to 'list_pop_front' on empty list")
		} else {}
		front {
			x = value
			front = next
		}
		if front == nil then {
			back = nil
		} else {}
	}
}

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

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

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