a.rs

use std::collections::{BTreeMap, BTreeSet};

type State = String;
type DeltaValue = BTreeMap<char, BTreeSet<State>>;
type Delta = BTreeMap<State, DeltaValue>;

fn main() {
    let mut delta: Delta = BTreeMap::new();
    let rules = [
        (("q0".to_string(), 'a'), "q1".to_string()),
        (("q0".to_string(), 'a'), "q2".to_string())
    ];
    
    for &((ref s,a), ref ns) in rules.iter() {
        let mut delta_value = match delta.get(s) {
            Some(value) => value.clone(),
            None => BTreeMap::new()
        };
        
        let mut next_states = match delta_value.get(&a) {
            Some(states) => states.clone(),
            None => BTreeSet::new()
        };
        
        next_states.insert(ns.clone());
        delta_value.insert(a, next_states);
        delta.insert(s.clone(), delta_value);
        
        

        println!("{:?}", delta);
    }
    
    
    let mut delta_value: DeltaValue = BTreeMap::new();
    let mut next_states: BTreeSet<State>= BTreeSet::new();
    
    next_states.insert("q1".to_string());
    delta_value.insert('a', next_states);
    delta.insert("q0".to_string(), delta_value);
    
    
    println!("{:?}", delta);
}