feat: start of lift, debugging, cleanup

exm/zelus/ballz/ballz.zls

@@ -0,0 +1,19 @@
+let g = 9.81
+let y0 = 50.0
+let y'0 = 0.0
+
+let hybrid ball (y0, y'0) = y where
+  rec der y  = y'   init y0
+  and der y' = -. g init y'0 reset z -> -0.8 *. (last y')
+  and z = up(-. y)
+
+let hybrid main () =
+  let der t = 1.0 init 0.0 in
+  let y = ball (y0, y'0) in
+  let z = period(0.01) in
+  present z -> (
+    print_float t;
+    print_string "\t";
+    print_float y;
+    print_newline ()
+  ); ()