* turing-machine
[[https://melpa.org/#/turing-machine][file:https://melpa.org/packages/turing-machine-badge.svg]]
[[https://stable.melpa.org/#/turing-machine][file:https://stable.melpa.org/packages/turing-machine-badge.svg]]
[[https://www.gnu.org/licenses/gpl-3.0.txt][file:https://img.shields.io/badge/license-GPL_3-green.svg]]

Implementation of a single tape turing machine simulator in emacs-lisp and
python (separately).

Inspired by http://morphett.info/turing/turing.html

** Usage
*** Syntax
The syntax for turing code is described in the link above, but for redundancy:
#+begin_quote
Syntax:

   - Each line should contain one tuple of the form ~<current state> <current symbol> <new symbol> <direction> <new state>~.
   - You can use any number or word for ~<current state>~ and ~<new state>~, eg. ~10~, ~a~, ~state1~. State labels are case-sensitive.
   - You can use any character for ~<current symbol>~ and ~<new symbol>~, or ~_~ to represent blank (space). Symbols are case-sensitive.
   - ~<direction>~ should be ~l~, ~r~ or ~*~, denoting 'move left', 'move right' or 'do not move', respectively.
   - Anything after a ~;~ is a comment and is ignored.
   - The machine halts when it reaches any state starting with ~halt~, eg. ~halt~, ~halt-accept~.

Also:

   - ~*~ can be used as a wildcard in ~<current symbol>~ or ~<current state>~ to match any character or state.
   - ~*~ can be used in ~<new symbol>~ or ~<new state>~ to mean 'no change'.
   - ~!~ can be used at the end of a line to set a breakpoint, eg ~1 a b r 2 !~. The machine will automatically pause after executing this line.
   - You can specify the starting position for the head using ~*~ in the initial input.
#+end_quote
The [[./examples]] directory should contain relevant examples. Source should be
listed near the top when not my own.
*** Python
Write a file with the syntax above, and pass it to the script as indicated
below. This is in Python 3. It should be pretty trivial to implement in
python 2.
#+begin_example
Usage:
  turing_machine.py FILENAME INITIAL
  turing_machine.py FILENAME INITIAL [-r|--rate] [RATE]

Options:
  -h --help
  -r --rate  specify delay rate
#+end_example
*** Emacs
- Write a file/buffer with the syntax described above, and run
  ~turing-machine-execute~ to run the simulator.
- Add ~-*- mode: turing-machine -*-~ to the top of the file to automatically
  start in ~turing-machine-mode~ when you next open the file.
- In ~turing-machine-mode~ you can press ~C-c C-c~ (~turing-machine-execute~) to start the machine.
- Within the code file, you can use ~;; INITIAL: [Some initial state]~ to denote
  the initial state and ~;; RATE: [some number]~ to denote the update rate
  in seconds.
  + If intial state is not set, you will be prompted for it through the
    minibuffer. To be prompted anyway, call ~turing-machine-execute~ with a
    prefix argument ~C-u~.
  + If rate is not set, it will default to the fastest speed (this is still
    pretty slow). With a double prefix argument ~C-u C-u~, you will be prompted
    for rate through the minibuffer
- Spaces are allowed in initial input, but surrounding spaces are trimmed. You
  can be explicit with ~_~.
- You can choose to hide visualization of spaces with an underscore by setting
  ~turing-machine-visual-spaces~ to ~nil~.
** Emacs Installation
This package is on Melpa. To install using [[https://github.com/jwiegley/use-package][use-package]]:
#+begin_src emacs-lisp
(use-package turing-machine
  :ensure t)
#+end_src

Using [[https://github.com/quelpa/quelpa-use-package][quelpa-use-package]]:
#+begin_src emacs-lisp
(use-package turing-machine
  :quelpa (turing-machine
           :fetcher github
           :repo "therockmandolinist/turing-machine"))
#+end_src

Or [[https://github.com/quelpa/quelpa][quelpa]]:
#+begin_src emacs-lisp
(quelpa '(hacker-typer
          :fetcher github
          :repo "therockmandolinist/turing-machine"))
#+end_src

Otherwise, download the files to somewhere on your load path, and enable
turing-machine:
#+begin_src emacs-lisp
(require 'turing-machine)
#+end_src

** Todo
 - Better syntax highlighting.
 - Get rid of cursor in ~*turing-machine*~ buffer.
 - File extension