Substitutes a variable read from a YAML node with the value stored in Fabric's ``env`` dictionary. Creates an
    object for late resolution.

    :param loader: YAML loader.
    :type loader: yaml.loader.SafeLoader
    :param node: Document node.
    :type node: ScalarNode
    :return: Corresponding value stored in the ``env`` dictionary.
    :rtype: any

def expand_env_lazy(loader, node):
    """
    Substitutes a variable read from a YAML node with the value stored in Fabric's ``env`` dictionary. Creates an
    object for late resolution.

    :param loader: YAML loader.
    :type loader: yaml.loader.SafeLoader
    :param node: Document node.
    :type node: ScalarNode
    :return: Corresponding value stored in the ``env`` dictionary.
    :rtype: any
    """
    val = loader.construct_scalar(node)
    return lazy_once(env_get, val)