Turing machine simulator

This is a Turing machine simulator. To use it:

Load one of the example programs, or write your own in the Turing machine program area. See below for syntax.
Enter something in the 'Input' area - this will be written on the tape initially as input to the machine. Click 'Reset' to initialise the machine.
Click on 'Run' to start the Turing machine and run it until it halts (if ever). Click on 'Pause' to interrupt the Turing machine while it is running. Alternately, click 'Step' to run a single step of the Turing machine.
Click 'Reset' to restore the Turing machine to its initial state so it can be run again.

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 almost any character for <current symbol> and <new symbol>, or '_' to represent blank (space). Symbols are case-sensitive.
You can't use ';', '*', '_' or whitespace as symbols.
<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.