The possibility to offload, via a platform-agnostic specification, the execution of (some/part of the) control functions down to the switch and operate them at wire speed based on packet level events, would yield significant benefits in terms of control latency and reaction times, meanwhile retaining the SDN-type ability to program and instantiate a desired network operation from a central controller. While programmability inside the switches, at wire speed and using platform-independent abstractions, of "any possible'" control function seems well beyond the OpenFlow capabilities, in this paper we argue that a non trivial sub-class of stateful control functions, namely those that can be abstracted in terms of Mealy (Finite State) Machines, is already compatible with off-the-shelf OpenFlow version 1.1+ Hardware with marginal architectural modifications. With minimal additional hardware circuitry, the above sub-class can be extended to include support for bidirectional/cross-flow state handling. We demonstrate the viability of our proposed approach via two proof-of-concept implementations (hardware and software), and we show how some stateful control functionalities frequently exploited in network protocols are readily deployed using our application programming interface.