Why would you claim composable futures are indeed a component of FRP? I find no mention of this in Elliott's and/or Hudak's description of FRP.

Edit:

Conal adds a notion of future values in his push/pull work, but I wonder if it is the same thing as being discussed here, as composable futures were around long before FRP:

http://conal.net/papers/push-pull-frp/push-pull-frp.pdf