To compute the position of the point, we integrate the velocity.

let process compute_pos state =
  loop
    let p = last ?state.pos +: last ?state.vel in
    emit state.pos p;
    pause
  end

So, to move a point from left to right, we define a process which maintains the velocity of a point at each instant.

let process left_right state =
  loop emit state.vel (2.0, 0.); pause end

To observe the position of a point, we define a process draw which emits the state of a point at each instant.

let process draw state =
  loop
    emit to_draw state; pause
  end