A Minimalistic Turing Machine

turing_machine.py

"""
A minimalistic Turing machine I wrote for an assignment.

Has 4 commands: > (unconditional branch), + (add), x (halt), and ? (branch if zero). > adds to the current
tape location by x, where x is the number right after the command. + adds the number in absolute
position a to the number in absolute position b, one-indexed, where a and b are the two numbers 
following the command. x stops the program and prints the contents of the tape. ? checks if the previous
number is zero, if it is, add x to the tape position, where x is the number following the command.

Sample multiplication program: > 7 c a b ? 4 > 3 x + 4 3 -1 + 14 5 > -13, where c is the result
(initially set to 0), and a and b are the two numbers to multiply
"""

raw = input().split()
tape = []
for n in raw:
    try:
        tape.append(int(n))
    except ValueError:
        tape.append(n)
head = 0
stop = False
while not stop:
    match tape[head]:
        case '>':
            head += tape[head + 1]
        case 'x':
            stop = True
        case '+':
            tape[tape[head + 2] - 1] += tape[tape[head + 1] - 1]
            head += 1
        case '?':
            if tape[head - 1] == 0:
                head += tape[head + 1]
            else:
                head += 1
        case _:
            head += 1
print(tape)