brainfuck interpreter in rust

main.rs

use std::env;
use std::fs;
use std::io::{self, Write, Read};
use std::process::exit;

fn main() {
    let args: Vec<String> = env::args().collect();
    let contents: String = match fs::read_to_string(&args[1]) {
        Ok(x) => x,
        Err(e) => {
            eprintln!("{:?}", e);
            exit(1);
        }
    };
    let contents: &[u8] = contents.as_bytes();

    let mut tape: Vec<u8> = vec![0u8; 30000];
    let mut ptr: usize = 0;
    let mut unmatched: i32 = 0;
    let mut i: usize = 0;

    loop {
        let ch: char = match contents.get(i) {
            Some(t) => *t as char,
            None => exit(0)
        };
        match ch {
            '>' => {
                ptr += 1;
            }
            '<' => {
                ptr -= 1;
            }
            '+' => {
                tape[ptr] = tape[ptr].wrapping_add(1);
            }
            '-' => {
                tape[ptr] = tape[ptr].wrapping_sub(1);
            }
            '.' => {
                io::stdout().write(&[tape[ptr]]).unwrap();
            }
            ',' => {
                let mut buf: [u8; 1] = [0u8; 1];
                io::stdin().read(&mut buf)
                    .expect("h");
                tape[ptr] = buf[0];
            }
            '[' => {
                if tape[ptr] == 0u8 {
                    unmatched += 1;
                    while contents[i] as char != ']' || unmatched != 0 {
                        i += 1;
                        if contents[i] as char == '[' {
                            unmatched += 1;
                        } else if contents[i] as char == ']' {
                            unmatched -= 1;
                        }
                    }
                }
            }
            ']' => {
                if tape[ptr] != 0u8 {
                    unmatched += 1;
                    while contents[i] as char != '[' || unmatched != 0 {
                        i -= 1;
                        if contents[i] as char == ']' {
                            unmatched += 1;
                        } else if contents[i] as char == '[' {
                            unmatched -= 1;
                        }
                    }
                }
            }
            _ => {}
        }
        i += 1;
    }
}