# turingsim

a quick and dirty turing machine simulator, written in C89.

[turingsim in compudanzas](https://compudanzas.net/turingsim.html)

# build and run

to build:

```
make build
```

or

```
cc -std=c89 -Wall turingsim.c -o turingsim
```

to run with an input file:

```
./turingsim machines/parentesis.txt | less
```

# input file fields

the line-based fields are:

* initial state
* inital tape
* initial position of head on tape (starting at 0)
* number of rules
* list of rules, in the form: state, symbol, new state, new symbol, direction (even is right, odd is left)
* maximum number of simulation steps

# example input file

this input file corresponds to the "comprobador de paréntesis" machine described in [máquinas de turing](https://compudanzas.net/máquinas_de_turing.html)

```
a
A(()())A
1
11
a)bX1
a(a(0
aAcA1
aXaX0
b)b)1
b(aX0
bAH00
bXbX1
c(H00
cAH10
cXcX1
80
```

## example output

the output for this example file looks as follows:

```
parentesis.txt
initial state: a
initial tape: A(()())A
initial position of head: 1
number of rules: 11
rule number 0: a)bX1
rule number 1: a(a(0
rule number 2: aAcA1
rule number 3: aXaX0
rule number 4: b)b)1
rule number 5: b(aX0
rule number 6: bAH00
rule number 7: bXbX1
rule number 8: c(H00
rule number 9: cAH10
rule number 10: cXcX1
max number of simulation steps: 80

step 0
 a
A(()())A

step 1
  a
A(()())A

step 2
   a
A(()())A

step 3
  b
A((X())A

step 4
   a
A(XX())A

step 5
    a
A(XX())A

step 6
     a
A(XX())A

step 7
    b
A(XX(X)A

step 8
     a
A(XXXX)A

step 9
      a
A(XXXX)A

step 10
     b
A(XXXXXA

step 11
    b
A(XXXXXA

step 12
   b
A(XXXXXA

step 13
  b
A(XXXXXA

step 14
 b
A(XXXXXA

step 15
  a
AXXXXXXA

step 16
   a
AXXXXXXA

step 17
    a
AXXXXXXA

step 18
     a
AXXXXXXA

step 19
      a
AXXXXXXA

step 20
       a
AXXXXXXA

step 21
      c
AXXXXXXA

step 22
     c
AXXXXXXA

step 23
    c
AXXXXXXA

step 24
   c
AXXXXXXA

step 25
  c
AXXXXXXA

step 26
 c
AXXXXXXA

step 27
c
AXXXXXXA

step 28
 H
1XXXXXXA
halted
```

the 1 written at the end indicates that the parenthesis sequence was well-formed. if there was a parenthesis without its pair, the machine would have written 0 instead.