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#[derive(Copy, Clone, PartialEq, Eq)] pub enum SeekPos { TopFirst, TopLast, BottomFirst, BottomLast, } #[derive(Copy, Clone, PartialEq, Eq)] pub enum NavigateDir { Up(bool), Down, Left, Right, } pub trait BiIterator: Iterator { fn prev(&mut self) -> Option<Self::Item>; } pub trait Navigator { type Item; fn navigate(&mut self, dir: NavigateDir) -> Option<Self::Item>; fn seek(&mut self, pos: SeekPos) -> Option<Self::Item>; fn down(&mut self) -> Option<Self::Item> { self.navigate(NavigateDir::Down) } fn right(&mut self) -> Option<Self::Item> { self.navigate(NavigateDir::Right) } fn left(&mut self) -> Option<Self::Item> { self.navigate(NavigateDir::Left) } fn up(&mut self) -> Option<Self::Item> { self.navigate(NavigateDir::Up(true)) } fn exit(&mut self) -> Option<Self::Item> { self.navigate(NavigateDir::Up(false)) } }