expanded-main.rs

use std::io::*;

fn main() {
    loop{
        let mut l = String::new();
        let mut a = 0;

        print!(">> ");
        stdout().flush().unwrap();
        stdin().read_line(&mut l).unwrap();

        for c in l.chars() {
            match c {
                'i'|'x' => a += 1,
                'd' => a -= 1,
                's'|'k' => a *= a,
                'o' => println!("{}", a),
                _ => {}
            }
            match a {
                -1|256 => a = 0,
                _ => {}
            }
        }
    }
}

main.rs

use std::io::*;fn main(){loop{let mut l=String::new();let mut a=0;print!(">> ");stdout().flush().unwrap();stdin().read_line(&mut l).unwrap();for c in l.chars(){match c{'i'|'x'=>a+= 1,'d'=>a-=1,'s'|'k'=>a*= a,'o'=>println!("{}",a),_=>{}}match a{-1|256=>a=0,_=>{}}}}}

Deadfish interpreter written in Rust.
266 characters for code golf.
https://codegolf.stackexchange.com/questions/16124/write-an-interactive-deadfish-interpreter