Hanoi Love interpreter.

hanoi_love.py

'''
I couldn't find a modern interpreter for Hanoi Love so here goes.
@author     Ngoc N. Tran (@ngoctnq)
@created    November 2nd, 2021
'''

from typing import Union

def run_hl(instructions: str, stdin: Union[list, bytes] = []):
    '''
    Run the Hanoi Love program.
    
    Parameters:
    :param instructions    : the program instructions
    :param stdin (optional): the stdin to pipe into the program
        may be a list or anything that can be converted into a list
    '''
    stacks = [[], [], [], []]
    stack_idx = 0
    register = 0
    skipping = False
    iomode = False
    insptr = 0
    output = []
    if type(stdin) is not list:
        stdin = list(stdin)
        
    while True:
        if insptr == len(instructions):
            return bytes(output)
        c = instructions[insptr]
        insptr += 1
        if skipping:
            if c == '!':
                skipping = False
            continue
            
        if c == '.':
            stack_idx = (stack_idx + 1) % 4
        elif c == "'":
            if iomode:
                output.append(register)
                iomode = False
            elif stack_idx == 3:
                stacks[3].append(insptr - 2)
            else:
                stacks[stack_idx].append(register)
                
        elif c == ',':
            if iomode:
                register = stdin.pop(0)
                iomode = False
            elif len(stacks[stack_idx]) == 0:
                if stack_idx == 0:
                    register = 1
                    continue
                if stack_idx < 3:
                    register = 0
                    continue
                raise
            elif stack_idx == 3:
                insptr = stacks[3].pop()
            else:
                register = stacks[stack_idx].pop()
                
        elif c == ';':
            if iomode:
                register += stdin.pop(0)
                iomode = False
            elif len(stacks[stack_idx]) == 0:
                if stack_idx == 0:
                    register += 1
                    continue
                if stack_idx < 3:
                    continue
                raise
            elif stack_idx == 3:
                stacks[stack_idx].pop()
            else:
                register += stacks[stack_idx].pop()
                
        elif c == '`':
            if iomode:
                register -= stdin.pop(0)
                iomode = False
            elif len(stacks[stack_idx]) == 0:
                if stack_idx == 0:
                    register -= 1
                    continue
                if stack_idx < 3:
                    continue
                raise
            elif stack_idx == 3:
                stacks[stack_idx].pop()
            else:
                register -= stacks[stack_idx].pop()
                
        elif c == '"':
            iomode = True
            
        elif c == ':':
            if register == 0:
                skipping = True
                
        elif c == '!':
            return bytes(output)
                
            
if __name__ == '__main__':
    assert run_hl('''.'...,;';';;';';';'.,...;"'.'...,;;';;';';;'.,...;"';;;;;;;"'"';;;"'.'.,...'...,;';';';';'.,...;"'..'...,'...,;;';';';'.,...`"'.'...,;;';';';'.,...;"';;;"'``````"'````````"'.'.,..;"'.'.,..;;;;;;;;;;"\'''') == b'Hello World!\n'