BGP has long been the de-facto control plane protocol for inter-network connectivity. Although initially designed to provide best-effort routing between ASes, the evolution of Internet services has created a demand for more complex control functionalities using the protocol. At the heart of this challenge lies the static nature of configuration mechanisms and the limited programmability of existing BGP speakers. Meanwhile, the SDN paradigm has demonstrated that open and generic network control APIs can greatly improve network functionality and seamlessly enable greater flexibility in network management. In this paper, we argue that BGP speaking systems can and should provide an open and rich control and configuration mechanism, in order to address modern era network control requirements. Towards this goal, we present λbgp, a modular and extensible BGP framework written in Haskell. The framework offers an extensible integration model for reactive BGP control that remains backward compatible with existing BGP standards and allows network managers to define route processing policies using a high-level language and to dynamically inject information sources into the path selection logic. Using a high-performance BGP traffic generator, we demonstrate that λbgp offers performance comparable to production BGP speakers, while dynamic AS route processing policies can be written in just a few lines of code.