This hack simulates a single-tape Turing machine with an unbounded tape that can perform any sequence of the following operations:

• read the tape symbol
• write a symbol to the tape
• advance the (1D) tape in either direction

Inspiration

I wrote this hack during the review tutorial for the CS 145 final exam back in my first year of university. The TA jokingly mentioned that we could try implementing a Turing machine in Racket as practice for the final exam, and I was already ahead of him.

(We hadn't been taught a formal definition of a Turing machine during the course; it was merely raised as a model of computation along with other such models like lambda calculus.)

Extensions

One might imagine building a module on top of the hack to accept and run only valid programs according to some formulation of a Turing machine.