Brainfuck-pl is a project mainly written in Prolog, it's free.
A brainf*ck interpreter in Prolog
"From obscurity to oblivion"
This is our interpreter for the brainf*ck language, implemented in Prolog. Besides the beauty of Prolog, an implementation on top of a Prolog interpreter gives free tracing of brainfuck programs. This interpreter was written and tested with Sicstus Prolog 3.12.x.
Ego trip ;).