#![allow(dead_code, deprecated, unused_variables, unused_mut)]
#![feature(control_flow_ok)]
use std::ops::ControlFlow;
struct TreeNode<T> {
    value: T,
    left: Option<Box<TreeNode<T>>>,
    right: Option<Box<TreeNode<T>>>,
}
impl<T> TreeNode<T> {
    fn find<'a>(&'a self, mut predicate: impl FnMut(&T) -> bool) -> Result<&'a T, ()> {
        let mut f = |t: &'a T| -> ControlFlow<&'a T> {
            if predicate(t) { ControlFlow::Break(t) } else { ControlFlow::Continue(()) }
        };
        self.traverse_inorder(&mut f).break_ok()
    }
    fn traverse_inorder<'a, B>(
        &'a self,
        f: &mut impl FnMut(&'a T) -> ControlFlow<B>,
    ) -> ControlFlow<B> {
        if let Some(left) = &self.left {
            left.traverse_inorder(f)?;
        }
        f(&self.value)?;
        if let Some(right) = &self.right {
            right.traverse_inorder(f)?;
        }
        ControlFlow::Continue(())
    }
    fn leaf(value: T) -> Option<Box<TreeNode<T>>> {
        Some(
            Box::new(Self {
                value,
                left: None,
                right: None,
            }),
        )
    }
}
fn main() {
    let node = TreeNode {
        value: 0,
        left: TreeNode::leaf(1),
        right: Some(
            Box::new(TreeNode {
                value: -1,
                left: TreeNode::leaf(5),
                right: TreeNode::leaf(2),
            }),
        ),
    };
    let res = node.find(|val: &i32| *val > 3);
    assert_eq!(res, Ok(& 5));
}