iter-tree

This library provides an easy way to convert between iterators and tree structures in both directions. This can be useful when building simple parsers to convert a stream of token into a tree of token.

It extends iterators with two functions :

• tree that maps the iterator to an iterator of Tree that can be collected to a Tree.

• tree_deque that maps the iterator to an iterator of TreeDeque that can be collected to a TreeDeque.

  To get this one, you have to activate the deque feature flag.

Both type of trees implement the IntoIterator trait.

Usage

The creation of a tree is controlled with the BranchControl enum. This enum has three variants :

• BranchControl::Start
  • Is used to start nesting the items of the iterator into a new branch.
• BranchControl::Continue
  • Is used to keep the item in the same branch as the previous ones
• BranchControl::End
  • Is used to get back up to the previous branch to put the next items.

Note:

When filling a branch started with BranchControl::Start, no crash or error will happens if the iterator ends before encountering the corresponding BranchControl::End. Similarly, any unmatched BranchControl::End will simply be ignored.

If you want to check for these kind of situations, you can use a trick such as the depth counter showed in the below example.

Example

use iter_tree::prelude::*;

let mut depth = 0;

let before = String::from("a+(b+c)+d");

let tree: Tree<char> = before
    .chars()
    .into_iter()
    .tree(|&item: &char| match item {
        '(' => {
            depth += 1;
            BranchControl::Start
        },
        ')' => { 
            depth -= 1;
            BranchControl::End
        },
        _ => BranchControl::Continue,
    })
    .collect();

println!("{tree:#?}");

let after: String = tree.into_iter().collect();

assert_eq!(before, after);

Branch(
    [
        Leaf(
            'a',
        ),
        Leaf(
            '+',
        ),
        Branch(
            [
                Leaf(
                    '(',
                ),
                Leaf(
                    'b',
                ),
                Leaf(
                    '+',
                ),
                Leaf(
                    'c',
                ),
                Leaf(
                    ')',
                ),
            ],
        ),
        Leaf(
            '+',
        ),
        Leaf(
            'd',
        ),
    ],
)

Controllers

Additionally you can create a struct that implements the Controller trait to replace the closure from the previous example.

Here is an example of how this can be applied :

use iter_tree::prelude::*;

#[derive(Default)]
struct StackController<T> {
    stack: Vec<T>,
}

impl<T> StackController<T> {
    pub fn is_empty(self) -> bool {
        self.stack.is_empty()
    }
}

impl Controller<char> for &mut StackController<char> {
    fn control_branch(&mut self, item: &char) -> BranchControl {
        let &c = item;
        match c {
            '<' => {
                self.stack.push(c);
                BranchControl::Start
            }
            '(' => {
                self.stack.push(c);
                BranchControl::Start
            }
            '>' => {
                if self.stack.len() > 0 && self.stack.last().unwrap() == &'<' {
                    self.stack.pop();
                    BranchControl::End
                } else {
                    BranchControl::Continue
                }
            }
            ')' => {
                if self.stack.len() > 0 && self.stack.last().unwrap() == &'(' {
                    self.stack.pop();
                    BranchControl::End
                } else {
                    BranchControl::Continue
                }
            }
            _ => BranchControl::Continue,
        }
    }
}


let mut controller = StackController::default();

let _1 = "< ( < > ) >"
    .chars()
    .tree(&mut controller)
    .collect::<Tree<char>>();

assert!(controller.is_empty());

let mut controller = StackController::default();

let _b = "<(>)".chars().tree(&mut controller).collect::<Tree<_>>();

assert!(!controller.is_empty())

What's next ?

The goals for the future of this crate includes but are not limited to :

• Adding more methods to build Trees such as for example a tree_map and tree_deque_map method that would map the item before including it in the Tree.

• Providing other types of Trees, notably some that separate the item that inited and terminated a branch.