miniminisky/vm.py

#!/bin/bash env python3
"""
Reads stdin in full then interprets the instructions on each line as follows:
    - `DEC $R $S`: if register `$R` is > 0, decrement it, otherwise jump to state `$S`
    - `INC $R`: increments register `$R`
    - `.$STATE`: labels the current position as `$STATE` allowing transition from `DEC`.
      Note that the entirety of the line $STATE`, i.e. the name of the state _includes_
      the leading `.`
    - `HALT`: halts the machine and exits
    - `%`: debug instructions, e.g. printing program state

Any string is allowed for register names and state names as long as they don't contain
a space.

Comments are allowed via `#` where everything pass `#` and `#` itself is stripped out
prior to execution.
"""

from dataclasses import dataclass
from collections import Counter
import sys
import time

@dataclass
class Instruction:
    OP_DEC = 0
    OP_INC = 1
    OP_HALT = 2
    OP_STATE = 3
    OP_DEBUG = 99

    op: int
    pc: int
    source_line: str = None
    reg_arg: str = None
    state_arg: str = None

def main():
    program: list[Instruction] = []
    registers = Counter()
    # maps labels to PC counter values
    states: dict[str, int] = {}

    source_code = [l.strip() for l in sys.stdin.readlines()]

    pc = 0
    for line in source_code:
        line = line.split('#')[0]
        if len(line) == 0:
            continue

        tokens = line.split(' ')
        inst = None
        if tokens[0] == 'DEC':
            inst = Instruction(Instruction.OP_DEC, pc, line, reg_arg = tokens[1], state_arg=tokens[2])

        if tokens[0] == 'INC':
            inst = Instruction(Instruction.OP_INC, pc, line, reg_arg = tokens[1])

        if tokens[0] == 'HALT':
            inst = Instruction(Instruction.OP_HALT, pc, line)

        if tokens[0][0] == '.':
            inst = Instruction(Instruction.OP_STATE, pc, line)
            states[tokens[0]] = pc
        if tokens[0][0] == '%':
            inst = Instruction(Instruction.OP_DEBUG, pc, line)

        if inst is None:
            raise ValueError(f'Unknown instruction: {line}')

        program.append(inst)
        pc += 1

    print('Parsed program:')
    for state, pc_val in states.items():
        print(f'State {state:16s} pc={pc_val}')

    for idx, inst in enumerate(program):
        print(f'{idx:02d} {inst}')

    print('Executing...')
    pc = 0
    halted = False
    while not halted and pc >= 0:
        inst = program[pc]

        if inst.op == Instruction.OP_DEC:
            if registers[inst.reg_arg] == 0:
                pc = states[inst.state_arg]
            else:
                registers[inst.reg_arg] -= 1
                pc += 1

        if inst.op == Instruction.OP_INC:
            registers[inst.reg_arg] += 1
            pc += 1

        if inst.op == Instruction.OP_HALT:
            halted = True
            pc -= 1

        if inst.op == Instruction.OP_STATE:
            pc += 1

        if inst.op == Instruction.OP_DEBUG:
            pc += 1

            tokens = inst.source_line[1:].split(' ')
            if tokens[0] == 'print':
                if tokens[1] == 'reg':
                    for k in sorted(registers.keys()):
                        print(f'{k} = {registers[k]}', end=' ')
                    print()
            if tokens[0] == 'sleep':
                t = float(tokens[1])
                time.sleep(t)

if __name__ == '__main__':
    main()