def __call__(environ, router):
    """
        This callable triggers the router to process a raw WSGI environ dict
        into a response and controls the :app:`Pyramid` request pipeline.

        The ``environ`` is the raw WSGI environ.

        The ``router`` is an :class:`pyramid.interfaces.IRouter` object which
        should be used to create a request object and send it into the
        processing pipeline.

        The return value should be a :class:`pyramid.interfaces.IResponse`
        object or an exception that will be handled by WSGI middleware.

        The default execution policy simply creates a request and sends it
        through the pipeline, attempting to render any exception that escapes:

        .. code-block:: python

            def simple_execution_policy(environ, router):
                with router.request_context(environ) as request:
                    try:
                        return router.invoke_request(request)
                    except Exception:
                        return request.invoke_exception_view(reraise=True)
        """
