In fiddling with Turing Machines, there are many extensions that can be made. Multiple machines on a single tape, 2-dimensional tapes, multi-head, multi-tape machines, machines spawning other machines, non-deterministic rules: these are just a few possibilities.
ESC Quit
Enter Pause/Resume sim
S Progress the sim by single steps
-= Change sim speed
[] Zoom
M Toggle machine visibility
R Reset to initial state
Arrow Keys Move view around
Machines are described in text files, conventionally ending in .tm The format is as follows, where a blank symbol is represented by a backtick.
start_state
state s -> newstate n M [* childpath [x,y [childstate]]]
The first line contains the name of the start state. The remaining lines until EOF each contain a single transition rule where if the machine is in state, scanning the symbol s on the tape, it will transition to newstate, write n down in place of s, and move along the tape in a direction determined by M, which is a string of L, R, U, D, or H. H causes the machine to halt. childpath is a relative path to the machine to be spawned as a child of this one. The child machine will be created in the same location as the parent, before it moves, offset by x,y squares, starting in childstate, if those arguments are given. If they are not, the machine will not be offset, and it will begin in its usual start state. The leading * is required, since it defines the delimiter between multiple children. Hence, any number of children is allowed for a given rule.
If s is longer than a single character, a rule will be created for each character in the string. Hence, A 012 -> B 3 R is equivalent to:
A 0 -> B 3 R
A 1 -> B 3 R
A 2 -> B 3 R
If n is "~", the machine will not change the symbol in that position. This also works with multicharacter scanned symbols, so that A 01 -> B ~ R yields the same result as:
A 0 -> B 0 R
A 1 -> B 1 R
If n is a string, a single character from it will be chosen arbitrarily to be used upon each invocation of that rule. Each character has equal probability of being selected.
If M is multiple characters long, the machine will execute each move in sequence. For example a value of URR will cause the machine to move diagonally one square up and two squares right. an H will cause the rest of the string to be discarded, hence UHU is equivalent to UH. Any undefined symbol in M will not produce any effect.
Lines beginning with a # are interpreted as comments and are ignored, along with whitespace.