from bu4.evaluation.enull import ENull
from bu4.codes import CODE_NULL
from bu4.parsing.linked import Linked, LinkingState, Parsed
from bu4.linking.linkingfinished import LinkingFinished
from bu4.evaluation.aftervalue import envtype, Evaluable


__all__ = ('LNull', 'PNull',)


class LNull(Linked):
    def __init__(self):
        self.future = set()

    def link(self) -> LinkingState:
        return LinkingFinished(self)

    def evaluable(self, env: envtype) -> Evaluable:
        return ENull()

    def __str__(self):
        return '?'

    def unlink(self) -> Parsed:
        return PNull()


class PNull(Parsed):
    def link(self, promise: set[bytes]) -> 'Linked':
        return LNull()

    def __bytes__(self):
        return bytes([CODE_NULL])