Matching Braces in Rust with a Stack

braces.rs

// you'll need to install lazy_static crate for this code to work, so put this into your Cargo.toml:
// 
// [dependencies]
// lazy_static = "*"

#[macro_use]
extern crate lazy_static;
use std::collections::{HashMap, HashSet};

lazy_static! {
    static ref PARENS: HashMap<char, char> =
        [('(', ')'), ('{', '}'), ('[', ']')].into_iter().collect();
    static ref ALL_PARENS: HashSet<char> = PARENS.keys().chain(PARENS.values()).cloned().collect();
}

fn is_parenthesis(ch: char) -> bool {
    ALL_PARENS.contains(&ch)
}

fn is_matching(opening: char, closing: char) -> bool {
    if let Some(actual_closing) = PARENS.get(&opening) {
        *actual_closing == closing
    } else {
        false
    }
}

fn is_balanced(input: &str) -> bool {
    let mut stack = vec![];

    for ch in input.chars() {
        if is_parenthesis(ch) {
            match stack.last() {
                Some(&opening) if is_matching(opening, ch) => {
                    stack.pop();
                }
                _ => stack.push(ch),
            }
        }
    }

    stack.is_empty()
}

fn main() {
    dbg!(is_balanced("([]{()})"));
    dbg!(is_balanced("([yo, foo]{(14)*89})"));

    dbg!(is_balanced("([]{)})"));
    dbg!(is_balanced("([yo, foo]{)*89})"));

    dbg!(is_balanced("([]{()})]"));
    dbg!(is_balanced("([]{(})"));
}