>  > Looks like a pretty nice solution, except I think (but didn't confirm)
>  > there is one problem:
> 
>  > >       @head += (dir == 'R') ? 1 : -1
> 
>  > Doing this could cause the head to wrap around, since array[-1] in
>  > Ruby is the last element of the array. It's likely the examples won't
>  > exercise this constraint, but the tape should not loop...
> 
>  That could be a problem, but I cheated: @tape is actually a hash. (I
>  was lazy and didn't want to make a Tape class or add extra logic to
>  deal with going past the front of the tape.)

Ah, well played, sir. I concede the point. :)