fn parse(mut input: Vec<Token>)-> Result<(), Box<dyn std::error::Error>> {

    while let Some((index, item)) = input.iter().enumerate().next() {
       "cd" => {
           println!("cd");
           let dir = Path::new(input.peekable()
                                            .peek()
                                            .map_or("/", |val| *val));
           // try to set to new dir, otherwise root
           if let Err(e) = env::set_current_dir(&dir) {
               return Err(Box::from(e))
           }
           else {
               return Ok(())
           }
       },
       "exit" | "q" => {
           std::process::exit(1);
       },
       command => {
           println!("command");
           let mut child = Command::new(command)
                                   .args(input)
                                   .spawn()?;

           let code = child.wait();
           if code.is_err(){
               Err(format!("error executing, code {}", code.unwrap()).into())
           }
           else {
               Ok(())
           }
       },
   }
   Ok(())
}