brainfuck.rs

use std::io;

static MEM_SIZE: uint = 30_000;

fn main() {
    // Initialize the memory with 30 000 0 bytes.
    let mut memory = [0 as u8, ..MEM_SIZE];

    // The current "cell" we're in, in memory.
    let mut pointer = 0;

    // The instruction list, a vector of characters.
    let mut instructions = vec!();

    for command in io::stdin().chars() {
        let instruction = command.unwrap();

        match instruction {
            // It's a valid command, append it to our instruction list.
            '>'|'<'|'+'|'-'|'['|']'|'.'|'#' => instructions.push(instruction),

            // It isn't a valid command, don't add it to the instruction
            // list.
            _ => {}
        }

        // The "#" indicates the end of a program.
        if instruction == '#' {
            break;
        }
    }

    // The current position we are in the instruction list.
    let mut index = 0;

    // Keep track of where the open "[" are located as indexes in the
    // instruction list.
    let mut open = vec!();

    loop {
        let instruction = *instructions.get(index);

        match instruction {
            // Move the pointer right one cell.
            '>' => pointer += 1,

            // Move the pointer left one cell.
            '<' => pointer -= 1,

            // Increment the current memory position by one.
            '+' => memory[pointer] += 1,

            // Decrement the current memory position by one.
            '-' => memory[pointer] -= 1,

            // Skip ahead to the next "]" if the current cell is 0.
            '[' => {
                open.push(index);
            },

            // Go back to the previous "[" unless the current cell is 0.
            ']' => {
                if memory[pointer] != 0 {
                    index = *open.last().unwrap();
                } else {
                    open.pop();
                }
            },

            // Print the current memory position as a character.
            '.' => print!("{}", memory[pointer] as char),

            // End the program.
            '#' => break,

            // An unknown character (this shouldn't happen).
            _ => {}
        }

        index += 1;
    }
}