Synchronous reactive programming gives reactive systems a deterministic temporal structure by organizing execution into logical instants and signal-based communication. The lineage from Boussinot’s synchronous reactive model to ReactiveML extends this discipline with cooperative threads, broadcast signals, dynamic processes, and higher-order functional programming. We present Tempo, a synchronous reactive programming library for OCaml 5 built on algebraic effects and deep handlers. The library reconstructs the core runtime mechanisms exposed as ReactiveML constructs as an ordinary OCaml 5 library rather than as a dedicated language extension: effect operations mark reactive suspension points, and the handler turns captured continuations into scheduler tasks. We evaluate this design through a comparative study with ReactiveML.