I don't think you can do this without a form of recursive behaviour and hence a way to introduce infinitesimal delay to fix recursive definitions. Assuming you don't deal with acceleration at a given time t you have : collisions depends on position position depends on velocity velocity depends on collisions This has no least fixed point at time t. To break the tight loop you must introduce an infinitesimal delay in one of the dependencies. Note that doing the same as you do (see the p.s. below) made me doubt a little bit on the appropriateness of frp for physics simulations. The problem is that physics simulations are dirty with respect to time (at least as implemented traditionnaly). Dirty in the sense that you update positions according to your time step and once you realize that you went to far (i.e. across a collider) you come back in the past until the point of contact, invoke collision response, and start this again until your system stabilizes at the end of the time step. In my breakout game the system is ad-hoc, I tried to factor out a more general system where collision detection and collision response would be nicely separated, as is usual in physics engines, but didn't really succeed; at least not without introducing a lot of intermediary behaviours. This lead me to think that maybe implementing the simulation more traditionnaly and give it an frp interface to implement the game logic to be feedback in the simulation would be a better approach. As I said elsewhere I'd love to be proven wrong i.e. that implementing physics simulation in frp itself is feasible and worthwhile. Maybe my lack of experience with frp is just showing, as is my experience with physics engines, and I'd be interested to know if anybody comes with interesting and non-contrived frp solutions to these problems. Best, Daniel P.S. There's an ANSI terminal breakout [1] in the examples of my own OCaml frp library. It uses infinitesimally delayed behaviours to break the loop mentionned above. [1] http://erratique.ch/software/react/repo/test/breakout.ml