Code from the Tutorial Thursday hangout of 2 May 2013 on using mutual-recursion to represent automata.

The Scheme files in this repository:

recursion-refresher.scm refresher examples of recursion, mutual-recursion, and Scheme's 'letrec'

automata.scm three Scheme implementations of the deterministic finite automaton (DFA) from the Wikipedia page: http://en.wikipedia.org/wiki/Deterministic_finite_automaton

automata-mk.scm translation of the second DFA implementation from automata.scm into the miniKanren relational language

automata-mk2.scm translation of the third DFA implementation from automata.scm into the miniKanren relational language

Support files:

pmatch.scm a simple pattern matcher

test-check.scm a simple test macro

mk.scm an implementation of miniKanren

The YouTube video of hangout is at: https://www.youtube.com/watch?v=yrf1AYtrKm0

In the video I demonstrate an old functional programming trick: how to encode a deterministic finite state automata using mutually recursive procedures in Scheme and miniKanren. I begin with a gentle introduction to recursion, mutual recursion, and Scheme's letrec construct, which experienced functional programmers may wish to skip.

If you find this interesting, you might want to read Shriram Krishnamurthi's 2006 Journal of Functional Programming paper, 'Automata via Macros': http://cs.brown.edu/~sk/Publications/Papers/Published/sk-automata-macros/

Michael Sipser's overpriced but excellent 'Introduction to the Theory of Computation, third edition' contains the clearest explanation of finite automata I have seen.

CHALLENGE:

Translate fsm-ho2 from automata.scm to miniKanren, without using project. (See the comment at the top of automata-mk2.scm) This should be possible by using a meta-circular interpreter that can run miniKanren inside miniKanren. This interpreter would also need to handle the subset of Scheme used in the code, such as letrec.