From: Matthew Moss <matthew.moss@...>
Date: 2008-05-13T10:54:08+09:00
Subject: Re: The Turing Machine (#162)

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...