pvanheus/sendmail-turing repository overview

⁠A Turing machine based subtractor implemented in Sendmail

(on Github: https://github.com/pvanheus/sendmail-turing⁠)

In September 1998 I wrote a Turing machine⁠ simulator in Sendmail⁠. More info is archived in comp.mail.sendmail⁠. Unfortunately, setting up Sendmail is hard work for some, so now you can experiment with the code encapsulated in Docker. To run it do:

docker run --net=none -i -t pvanheus/sendmail-turing:latest

You'll get a prompt like:

local mailer defined
ADDRESS TEST MODE (ruleset 3 NOT automatically invoked)
Enter <ruleset> <address>
>

Enter a sum with something like tStart 1 1 0 1 (to do 2 - 1) and it will compute and show you the answer.

The 1 1 0 1 is a tape containing two numbers (2 and 1) in unary notation. The Sendmail email address rewriting language is (ab)used to create a simple automaton that moves back and forward on the tape, removing a 1 from the first number for each 1 that exists in the second number (this only works if the first number is greater than the second). Some limitations are explained in the original post.

Incidentially this subtraction with unary notation is somewhat similar to operations using Peano axioms. For a Scala introduction to Peano numbers see here⁠ and the succeeding posts here⁠, here⁠ and finally here⁠.

And in case you want to use this with Singularity⁠, here is a Singularity image⁠. So you can go:

singularity run sendmail-turing.img

(and wait a while for it to start, then use as above)