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fn main() { | |
// Linjie Zhang 2020 | |
// | |
// 3-state busy beaver | |
// https://en.wikipedia.org/wiki/Turing_machine | |
let rules = vec!["A01RB", "A11LC", "B01LA", "B11RB", "C01LB", "C11RH"] | |
.iter() | |
.map(|x| x.chars().collect::<Vec<char>>()) | |
.collect::<Vec<_>>(); | |
#[derive(Debug)] | |
struct Machine { | |
s1: Vec<char>, | |
s2: Vec<char>, | |
} | |
impl Machine { | |
fn new(state: char, symbols: Vec<char>) -> Self { | |
Self { | |
s1: vec![state], | |
s2: symbols, | |
} | |
} | |
fn state(&self) -> char { | |
*self.s1.last().unwrap() | |
} | |
fn symbol(&self) -> char { | |
*self.s2.last().unwrap() | |
} | |
fn set_state(&mut self, state: char) { | |
self.s1.pop(); | |
self.s1.push(state); | |
} | |
fn set_symbol(&mut self, symbol: char) { | |
self.s2.pop(); | |
self.s2.push(symbol); | |
} | |
fn print_tape(&self) { | |
let mut tape_left = self.s1.iter().collect::<String>(); | |
let l = tape_left.len(); | |
tape_left.truncate(l - 1); | |
let tape_right = self.s2.iter().rev().skip(1).collect::<String>(); | |
println!( | |
"state: {}\ntape: {}[{}]{}\n", | |
self.state(), | |
tape_left, | |
self.symbol(), | |
tape_right | |
); | |
} | |
fn to_left(&mut self) { | |
let state = self.s1.pop().unwrap(); | |
let n = self.s1.pop().unwrap(); | |
self.s2.push(n); | |
self.s1.push(state); | |
} | |
fn to_right(&mut self) { | |
let state = self.s1.pop().unwrap(); | |
let n = self.s2.pop().unwrap(); | |
self.s1.push(n); | |
self.s1.push(state); | |
} | |
fn transition(&mut self, rules: &Vec<Vec<char>>) { | |
let state = self.state(); | |
if state == 'H' { | |
panic!("halt"); | |
} | |
let symbol = self.symbol(); | |
for rule in rules { | |
if rule[0] == state && rule[1] == symbol { | |
self.print_tape(); | |
self.set_symbol(rule[2]); | |
if rule[3] == 'L' { | |
self.to_left(); | |
} else { | |
self.to_right(); | |
} | |
self.set_state(rule[4]); | |
return; | |
} | |
} | |
} | |
} | |
let mut left = vec!['0'; 6]; | |
left.push('A'); | |
let mut t_simple = Machine { | |
s1: left, | |
s2: vec!['0'; 6], | |
}; | |
loop { | |
t_simple.transition(&rules); | |
} | |
} |
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