Just went out and wrote a simple interpreter in 65 lines of Ruby. It's pretty slow but seems to be correct.<p>One thing you didn't mention is that the cells are supposed to be bytes, and thus increment and decrement need to be modulo 256. That may not be part of the actual definition but the sample programs I found all relied on it.<p>I also found it pretty funny that "apt-cache search brainfuck" returns a total of 3 interpreters in the Debian archive.