在Python中实现lisp

def car(lst):
    return lst[0]

def cdr(lst):
    return lst[1:]

def cons(x, lst):
    return [x] + lst

def add(args):
    return sum(args)

def sub(args):
    return args[0] - sum(args[1:])

def mul(args):
    result = 1
    for num in args:
        result *= num
    return result

def div(args):
    result = args[0]
    for num in args[1:]:
        result /= num
    return result

def eval(expr):
    if isinstance(expr, int):
        return expr
    elif expr[0] == 'quote':
        return expr[1]
    elif expr[0] == 'if':
        _, condition, true_expr, false_expr = expr
        if eval(condition):
            return eval(true_expr)
        else:
            return eval(false_expr)
    elif expr[0] == 'define':
        _, var, value = expr
        globals()[var] = eval(value)
    else:
        func = globals()[expr[0]]
        args = [eval(arg) for arg in expr[1:]]
        return func(args)

program = [
    ['define', 'x', 5],
    ['define', 'y', 3],
    ['define', 'result', ['add', 'x', 'y']],
    'result'
]

print(eval(program))  # 输出：8