fn count(x) ≔
  fold (+) 0 (([:1)"x);

fn isEven() :=
  (~ /(0|2|4|6|8)$/);

fn isOdd() :=
  (~ /(1|3|5|7|9)$/);

let
  val even := count (isEven #. $0)
  val odd := count (isOdd #. $0)
  val total := odd + even
in (total . even . odd) end