def countEvens n l :=
  match l as list integer with
    | ?isEven :: $tl -> countEvens (n + 1) tl
    | _ :: $tl -> countEvens n tl
    | [] -> n

def testNumbers :=
  let from n := if n <= 0 then [0] else n :: from (n - 1)
   in from 10000

countEvens 0 testNumbers