Hi, I'm programming a small game - amongst my types I have a 'world' structure data World = World Background [Lifeform] I'm calculating collisions between my player and the lifeforms, and I'll need this result both to allow some actions and to modify the world as a result. I'm using FRP with elerea, so everything is defined as behaviours (signals), and the collision signal is used in the signal accounting of life spent and in the world signal. I was thinking of returning a Traversal on the lifeforms that are colliding so that I can both access the lifeforms concerned (when performing actions and life accounting) and modify them as a result (for the world). Does that sound reasonable as a use of lenses? Overengineered? Better solutions? Thank you, Elise Huard