lispy.py

class sym:
    def __init__(self, name):
        self.name = name

    def __str__(self):
        return f":{self.name}"


def builtin_func(name):
    def inner(f):
        environment[name] = f

    return inner


def evl(lst, environment):
    print("evl", lst)
    if type(lst) in (int, str, float, list) or callable(lst):
        return lst
    elif type(lst) is sym:
        return environment[lst.name]
    elif type(lst) is tuple:
        if lst == ():
            return ()
        car, *cdr = tuple(evl(e, environment) for e in lst)
        if callable(car):
            print("calling", car, cdr)
            return car(*cdr)
        else:
            return car, *cdr


environment: dict[str, any] = {}


@builtin_func("if")
def if_(c, a, b):
    if c:
        return evl(tuple(a), environment)
    else:
        return evl(tuple(b), environment)


@builtin_func(">")
def gt(a, b):
    return evl(a, environment) > evl(b, environment)


evl(
    (sym("if"), (sym(">"), 1, 0), [print, "Hello world"], [print, "never called"]),
    environment,
)