let g  = 9.81
let p0 = 5.0
let v0 = 0.0

let hybrid ball () = (p, z) where
  rec der p = v    init p0 reset z -> 0.0
  and der v = -. g init v0 reset z -> -0.8 *. (last v)
  and z = up (-. p)

let hybrid main () =
  let der t = 1.0 init 0.0 in
  let rec der p = 1.0 init -0.01 reset q -> -0.01
      and q = up (last p) in
  let (b, z) = ball () in
  present q | z -> (
    print_float t; print_string "\t";
    print_float b; print_newline ()
  ); ()