Machination

A Turing machine description language, parser, and runtime

Syntax

The Turing machine is described with a dictionary structure. This could be a JSON object, or an equivalent Python dict. The fields of the root object each name a state or state-template. The state named "start" is the initial state of the execution, while any state featuring a 0 direction is a final state.

Symbol

A symbol is either:

a one character string
"NUL" (see alphabet)
"EOT" (see alphabet)
special strings depending on the context

Direction

A direction is either:

"left" or -1
"right" or 1
0 for a final state

Rule

A rule is an array with three fields: 0. a symbol to write

a direction to shift to
the name of a state or state-template to go to

In a rule, having the string "SAME" as the symbol means "write the same symbol than the one matched by the rule", essentially a noop tape-wise, while having the string "SAME" as the state means "go to the same state as the current one", essentially a noop state-wise.

State

A state is an object where each field is a named rule, named after the symbol to match.

In a state, having the string "ELSE" as the name of a rule means "duplicate this rule for every symbol not explicitely mentionned".

State-template

A state-template is a generic way to define similar states for information storage. A state-template is identified by terminating it with a .. Every instanciation of the state-template will be a state with a similar name, except with the final . replaced with the instanciation symbol.

State Rule leading to a state-template

In the rule of a regular state, the final dot of the state-template is replaced with the matched symbol. For an "ELSE" match, there will be one state-template instanciation for every matched symbol.

State-template rule

In a state-template, the string "DOT" where a symbol is expected (either in the name of a rule or as the write symbol of a rule) will be replaced with the instanciation symbol.

State-template rule leading to a state-template

In the rule of a state-template, the final dot of the state template is replaced with the instanciation symbol. This means that you can chain templates while retaining the same instanciation symbol.

Alphabet

The alphabet is given as input to the parser. On top of the given characters, two special symbols are injected in the alphabet:

"NUL" which symbolizes a empty space
"EOT" which symbolizes the end of the tape

Tooling

mtparser.py is a Python module that flattens the above description language. You can use it to turn a high level description of the Turing machine into a set of low level rules.

mtoutput.py is a Python module that turns the rules built by mtparser.py into text. There are 3 output drivers:

for humans
for mathematicians
for C compilers

machination is a frontend for the two modules above. It parses a JSON file describing a Turing machine, and rewrites it as plain rules. It can output the Turing machine as a C array into a header file.

mtruntime.c is a runtime for a rule array as output by machination. You can use the associated Makefile to turn your Turing machine into an executable.

Example

reverse.json contains an example of the description of a Turing machine that reverses a string. To use it:

$ ./machination -c reverse.json ASCII
Successfully written transition function as rules.h
$ make
cc -o mtruntime mtruntime.c
$ ./mtruntime "Hello world!"
!dlrow olleH

cigix/machination