from .formats import BaseFormat
from .tokens import *

class ExtractingFormat(BaseFormat):
    """Yields only the args to entities of the given style."""

    text_based = False

    def __init__(self, style):
        self.style = style

    def text(self, text):
        return ()
    def start(self, t, arg=None):
        return ()
    def end(self, t, arg=None):
        return ()

    def entity(self, t, arg=None):
        if t == self.style:
            yield arg

    def __call__(self):
        # We don't have any mutable state, so we can be a singleton.
        return self