brainfuck.rs

//! This is a Brainfuck parser and interpreter
//! Run it with the following command:
//! cargo run --example brainfuck -- examples/sample.bf

use chumsky::prelude::*;
use std::{
    env, fs,
    io::{self, Read},
};

#[derive(Clone)]
enum Instr {
    Invalid,
    Left,
    Right,
    Incr,
    Decr,
    Read,
    Write,
    Loop(Vec<Self>),
}

fn parser<'a>() -> impl Parser<'a, &'a str, Vec<Instr>, extra::Err<Simple<'a, char>>> {
    use Instr::*;
    recursive(|bf| {
        choice((
            just('<').to(Left),
            just('>').to(Right),
            just('+').to(Incr),
            just('-').to(Decr),
            just(',').to(Read),
            just('.').to(Write),
        ))
        .or(bf.delimited_by(just('['), just(']')).map(Loop))
        .recover_with(via_parser(nested_delimiters('[', ']', [], |_| Invalid)))
        // .recover_with(skip_then_retry_until([']']))
        .repeated()
        .collect()
    })
}

const TAPE_LEN: usize = 10_000;

fn execute(ast: &[Instr], ptr: &mut usize, tape: &mut [u8; TAPE_LEN]) {
    use Instr::*;
    for symbol in ast {
        match symbol {
            Invalid => unreachable!(),
            Left => *ptr = (*ptr + TAPE_LEN - 1).rem_euclid(TAPE_LEN),
            Right => *ptr = (*ptr + 1).rem_euclid(TAPE_LEN),
            Incr => tape[*ptr] = tape[*ptr].wrapping_add(1),
            Decr => tape[*ptr] = tape[*ptr].wrapping_sub(1),
            Read => tape[*ptr] = io::stdin().bytes().next().unwrap().unwrap(),
            Write => print!("{}", tape[*ptr] as char),
            Loop(ast) => {
                while tape[*ptr] != 0 {
                    execute(ast, ptr, tape)
                }
            }
        }
    }
}

fn main() {
    let src = fs::read_to_string(env::args().nth(1).expect("Expected file argument"))
        .expect("Failed to read file");

    match parser().parse(src.trim()).into_result() {
        Ok(ast) => execute(&ast, &mut 0, &mut [0; TAPE_LEN]),
        Err(errs) => errs.into_iter().for_each(|e| println!("{:?}", e)),
    };
}