An R7RS Scheme program for running Turing machines.
On the standard input put a description of:
- the alphabet,
- the state transition diagram,
- the state of the tape.
An example is:
"#+"
(skip (stop)
(skip (#\# #\# -> stop)
(#\+ #\+ -> skip)))
("+++#+" -1)
It consist of three s-expresions. The first is a string of two or more characters of which the first one is the one used to signify an empty position on the tape.
The state transition diagram is described as a list whose first element is the name of the starting state. The second is the list of names of the ending states. Consequent elements describe the 'intermediate' states.
The description of an intermediate state consist of it's name and the descriptions of transitions from it to other states. A transistion in turn is a list of four elements:
- the character that activates the transition upon being read,
- the character to overwrite it with,
- a left (
<-) or right (->) pointing arrow signifying the direction in which we will move over the tape, - the name of the next state.
Finally, we have a list containing a string describing the contents of the tape. It may optionally be followed by a number indicating how much and in which direction to shift over the tape with respect to the begining of the string.
Given the example input from before the program will produce the following output:
Machine in state skip
#+++#+
^
Machine in state stop
#+++#+
^
The errors reported might not be very helpful.
Copyright Bartosz Boguniewicz and Karol Marcjan 2013.
You can find more information on the terms under which this software
is provided in the LICENSE file distributed along with it.