The synchronous reactive model has been introduced in the 90's by Boussinot as a way to implement interactive systems as found in graphical user interfaces, video games or simulation problems. This models combines the synchronous model found in Esterel with features like dynamic creation of processes. This sildes presents a new calculus of synchronous reactive programs. This calculus is built above a call-by-value ML language. The main contribution is to provide it with a greedy operational semantics where computations are executed as soon as possible. Practical experiments show that this semantics leads to a very efficient execution of programs.