You could do a nested match like this
```rust
    match command {
        0x00E0 => Ok(Command::ClearScreen),
        0x00EE => Ok(Command::Return),
        _ => match command >> 12 { // get the first nibble
            1 => Ok(Command::Jump(self.val_u12)),
            2 => Ok(Command::Call(self.val_u12)),
            3 => Ok(Command::SkipIfRegVal(self.reg_x, self.val_u8)),
            _ => Err(()),
        },
    }
```